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Seed trays are essential for starting seeds and cuttings. Seed trays are commoly lightweight plastic, biodegrable paper, or compressed peat trays divided into separate cells, like a muffin tin, for growing individual seedlings.
Seed tray cells are usually 2 to 3 inches deep and up to 3 inches square or round. Some seed tray cells can be as small as 1 inch deep and 1 inch in diameter. Seed trays vary in size from small six packs (approximatley 4 by 8 inches) to as large as 12 by 20 inches or larger. Some seed trays come with a flat tray underneath to catch excess water. Some come with a plastic top or dome to create a small greenhouse.
There are many options available in the market. It can be overwhelming to know which one is the best fit for your needs. Here is a guide to seed trays and how they are used.
Biodegradable seed starting tray
Types of seed starting trays
Choose a seed tray that suits your specific needs. There are various types available, including individual cell trays, multi-cell trays, and open flat trays. Individual cell trays are ideal for larger seeds or plants that require ample space, as each cell provides enough room for seedlings to develop. Multi-cell trays are perfect for smaller seeds or plants that can be closely spaced, as they provide multiple compartments in which to sow your seeds. Open flat trays, on the other hand, are versatile and can accommodate seeds of various sizes, allowing for greater flexibility.
Plastic sectioned starting tray
Lightweight plastic tray divided into separate cells usually 2 to 3 inches deep and up to 3 inches square or round. Plastic trays can be very thin and light or heavier. Some have flexible bottoms that allow rooted seedlings to be pushed out of the tray from the bottom.
Sectioned fiber seed tray
Compressed paper fiber or peat trays are similar in size and depth to plastic trays. Sometimes sold with plastic trays that they fit beneath the setioned tray to catch water that drips through. Some are designed especially to fit onto windowsills, called windowsill sets.
Open trays or flats
Open trays or flats do not have individual cells. Flats are often 6 to 12 inches wide and 12 to 24 inches long. They can be used for starting very small seeds that can be broadcast or scattered across the the starting medium surface. Seedlings grown in open trays or flats often need thinning so that individual seedlings can grow on without competion from neighboring seedlings.
Self-watering seed trays
Self-watering seed trays have drainage holes and capillary matting. An outer tray without drainable holes fit into the bottom of the starting tray. The seedlings are watered indirectly &#; water put in the bottom tray is pulled up into the starting tray.
Seed trays with plastic covers
Seed trays with clear plastic covers provide extra climate control at the germianitng stage. The plastic cover or dome fits over the top of the starting tray. The plainest version of this starting tray looks something like a casserole dish. Some have high domes that allow seedlings to grow to 3 or 4 inches tall. Seed trays with clear plastic lids act as mini-greenhouses, creating a moist and warm environment ideal for germination. Others have adjustable vents that allow for temperature and humidity control. These features can be particularly useful if you are starting seeds in colder climates and want to extend your growing season.
Plastic seed starting tray with tomato seedlings
Seed tray use tips
Sow two or three seeds in each compartment to compensate for poor germination. If more than one seed germinates, thin out the weakest, leaving only one seedling in each section.
All seedlings in each tray should have the same watering requirements and planting times for ease of maintenance.
The growing medium should be premoistened before sowing seed.
Fiber or peat trays can be cut apart and completely buried in the garden (where the material will disintegrate nautrally). Trim off any part of the pot above soil line.
Seed tray material
Seed trays are commonly made of plastic or biodegradable materials. Plastic trays are durable, lightweight, and easy to clean, making them a popular choice among gardeners. Biodegradable trays, made from materials such as peat or coconut fiber, are environmentally friendly options that can be directly planted into the ground, preventing the disturbance of young plants during transplantation.
Plastic trays
Plastic trays are the most common choice due to their durability and affordability. They are lightweight, easy to clean, and provide good insulation for young plants. Plastic trays come in various sizes and designs. Plastic trays have excellent moisture retention, helping to create optimal conditions for seed germination. However, it is important to ensure that the plastic used is BPA-free to avoid any potential harm to your plants.
Some plastic trays are made from recycled materials such as recycled plastic or compostable materials; these are an excellent choice for reducing waste. Recycled trays often have the same benefits as traditional plastic trays, including durability and lightweight construction.
Biodegradable fiber or paper trays
Biodegradable trays made from materials like recycled paper, peat, or coconut coir are an eco-friendly alternative. These trays can be directly planted into the ground, reducing transplant shock and saving the gardener&#;s time and effort. Peat and fiber trays have excellent water retention capabilities and promote healthy root growth. Once seedlings are ready to be transplanted, the trays can be cut apart and the indivdual sectios can be planted directly into the ground. Peat and fiber trays can be more expensive than their plastic counterparts.
Seed tray with bottom tray to catch water
Seed tray depth
Seed trays can have cells of varying depth. Some types of plants have deeper root systems and require more space to grow, while others have shallower roots and can thrive in smaller cells. Make sure to choose a seed tray with the appropriate depth for the plants you are planning to grow.
Seed tray drainage
Seed trays must have drainage holes. Good drainage is essential for preventing waterlogging and ensuring healthy root development. Look for trays with good drainage capabilities to provide optimal conditions for your plants. Seed trays commonly have bottom drainage which allows excess water to easily escape. If water does not water easily drain away, seedling roots can become waterlogged and develop root rot. Bottom drainage allows for air circulation and prevents the build-up of harmful mold and fungus. Some seed trays feature small holes on the sides of the tray. This can provide a more controlled water supply to seeds.
Open tray or flat; seed is broadcast across the growing medium
Seed tray buying tips
Seed trays come in various sizes, ranging from compact ones with just a few cells to larger ones with dozens or even hundreds of cells. Consider the space you have available and the number of plants you intend to sow before making your decision. If you have limited space or are sowing a small number of seeds, a smaller seed tray would be appropriate. On the other hand, if you have a larger garden or are planning to sow a significant number of seeds, opting for a larger tray will give your seeds more room to grow and develop.
Ensure that the seed tray has adequate drainage holes. Proper drainage is crucial for seedling health as it prevents waterlogging, which can lead to root rot and other problems. Look for trays with sufficient drainage holes to ensure that excess water can easily escape, providing your seeds with the perfect balance of moisture.
Sectioned trays are more expensive than the single flat often used by many professional growers. Sectioned tays are worth the extra money because they prevent root competition among seedlings as roots can devleop only within confines of each section &#; thus reducing transplant shock.
Plastic trays can be reused year after year. Look for stiff, solid fabrication that will not easily break.
Self-watering trays are easy to use and worth the extra cost if you find watering on a regular schedule difficult.
Consider factors such as durability, moisture retention, and eco-friendliness when making your decision. By selecting the right seed tray material, you can create the ideal environment for your plants to thrive and ensure a successful gardening experience.
Seed trays we like
MIXC 10 Packs Seed Starter with Humidity Dome (120 Cells Total Tray) Growing Starting Seed Starting Trays Plant Starter and Base Mini Greenhouse Germination Kit. About $17.
RooTrimmer 3.5 inch Square Nursery Pots 60pcs, Sturdy seed starter trays 5 Pcs, Seeds Starting Germination, Small Planter Nursery Propagation 5 Sets. About $29.
9GreenBox &#; Seedling Starter Trays, 144 Cells: (24 Trays; 6-Cells Per Tray), Plus 5 Plant Labels. About $8.
RooTrimmer 54 Cell Seed Starter Trays &#; Sturdy and Deep Design, Perfect for Hydroponic Planting and Seed Starting (5-Pack). About $30.
Mr. Pen- Plastic Growing Trays, 5 Pack, Black, Seed Tray, Propagation Tray, Plant Trays for Seedlings, Planting Trays, Microgreens Trays, Seedling Starter Trays. About $15.
MIXC Seedling Trays Seed Starter Tray, 5-Pack Mini Propagator Plant Grow Kit Greenhouse with Humidity Vented Domes and Base for Seeds&#; Starting (40 Cells Per Tray, Total 200 Cells). About $17.
Seed Starter Tray, 24 Cells Indoor Seed Starter Kit, Flexible Silicone Designed Seedling Starter Trays, Germination Tray with Humidity Dome & Lids(4in Height), Reusable & Dishwasher Safe, BPA-Free. About $17.
Jucoan 40 Pack Peat Pots Seed Starter Trays, 480 Cells Germination Seedling Pots, Organic Biodegradable Plant Germination Tray. About $20.
GROWNEER 120 Cells Peat Pots Seed Starter Trays, 12 Packs Biodegradable Seedling Pots Germination Trays. About $12.
As a gardener, there is no end to what you could spend your money on. Take seed starting &#; what do you really need? Are those peat pellet kits really worth it? Can you start your seeds in yogurt tubs, or is that somehow not&#;.correct?
Here&#;s my opinionated opinion on what should get your money and what shouldn&#;t.
It should go without saying, but I&#;ll pound the point home anyway: better seeds make better seedlings. Good seeds needn&#;t be super expensive. In general, OP seeds cost less than hybrid seeds. I feel hybrid seeds offer an advantage for cauliflower and brussels sprouts, and in cool areas like the NW if you aren&#;t seed saving, you might opt for hybrids for the warm season crops like eggplant, peppers, and melons (because we need all the help we can get for those crops).
Otherwise, less expensive open pollinated varieties are a fine choice. For more info, or if seed selection is overwhelming you, check out my post on How to Pick Your Vegetable Seeds Without Going Crazy.
Start your early seeds on the kitchen windowsill? Maybe in the Southwest.
Here in Rainyside, grow lights will give a far superior result. See last year&#;s comparison between window-grown starts and grow-light starts for proof. We have T12 florescent grow lights. We upgraded to these T5 fluorescent grow grow lights in &#; they are a dream &#; and are currently () trialing LED lighting options to see if it finally makes financial sense for the home gardener to switch to LED grow lights .
Make your grow light decision based on what it right for you based on your space available, energy cost, and budget. Don&#;t forget that with lights there is an upfront budget and an operating budget, and in the long run it pays to get a more energy efficient setup.
If you are going to put lights on your seedlings, you want a little robot who will turn your lights on at 5 am and off at 10 pm without you having to remember. Make sure you get one with a grounded plug. You&#;re going to be spraying water around this thing, after all.
I love solid, heavy-duty plastic propagation trays. You do NOT need the inserts. Although the inserts are space efficient and I use them, almost any container can be modified into a seed starting container. Anything that can hold a bit of soil and a seed can be used as a pot, including newspaper, toilet paper tubes or old yogurt containers.
However, it is good practice to bottom water your seedlings, and I love the heavy duty solid trays for this. If you can find a bunch of old metal sheetpans with a sturdy, high lip all the way around, or have some plastic shoeboxes that will hold water, those all work well too. If you buy propagation trays, try to get them locally so you can inspect their sturdiness. It is worth paying a bit more for a really heavy duty tray that will last.
Fish Emulsion. Here, let me say it again: fish emulsion. This is the perfect liquid fertilizer for seed starting. I dilute to ¼ the recommended strength and bottom water seedlings with it every week or two, depending on the crop.
Once your crops are up and growing outside, if something looks like it needs help &#; dilute fish emulsion. If your spinach looks at you funny &#; dilute fish emulsion. Cilantro going to seed to fast? Dilute fish emulsion. Basically, fish emulsion is like lemon ginger tea: it might not be the exact perfect cure, but it won&#;t hurt, and it&#;ll probably make your plant feel better. When in doubt, dilute fish emulsion.
If you are starting your seeds in an out of the way area, I highly encourage you to introduce some constant airflow around your seedlings.
This does two very important things. First, it reduces the possibility of soil fungus and whitefly buildup around your seedlings. Second, constant light air movement forces seedlings to grow stronger and tougher, and put a bit more energy into growing a nice sturdy stem. It is important that your seedling&#;s first exposure to airflow isn&#;t a 45 mph wind gust just after your transplant them outside. I have a little soft bladed fan like this:
Not essential, but a seed heating mat is very nice to have if you are starting tomatoes, peppers or (especially) eggplant from seed in the Maritime Northwest. Obviously not needed if you live someplace where you put pepper seeds in the ground and they grow.
Warmer soil means a faster germination and less chance your heat-lovin&#; seeds are going to up and rot on you. I&#;ve had a pair of Hydrofarm seed mats like the one below for seven years, I use them every year, treat them like crap, and they&#;ve both held up very well. They are the same size as the propagation trays, so everything plays together really well on my seed-rack.
Ok, remember this is just my opinionated opinion. If you disagree, please feel free to (respectfully) make your case in the comments. Maybe you&#;ll change my mind!
Particularly the overpriced kind sold the small little bags from high-end nurseries in upscale malls. Grrrrr&#;..that kind of thing makes me cray-zay. If you only want to start five or six transplants, honestly you are probably better off just buying well-grown transplants from a good nursery. Once you get to the point where you start a lot of seeds indoors, you have to look at ways to make your seed starting medium more economical.
In the past I&#;ve used massive bags of standard Miracle Gro, Black Gold or E.B. Stone soilless potting mix and I&#;ve had great results with all of them. If your ethics allow it, the Miracle Gro is fine for seed starting. These days, my preferred potting soil is this DIY homemade mix.
My problem with dedicated seed starting mix in general is that I think it is too light and I don&#;t like the total lack of background nutrition. My goal isn&#;t just to get the maximum possible germination and growth from my seeds, as it might be for a commercial grower. My goal is to grow seedlings that will do well outside without forcing me to spend every waking minute babying my transplants.
A slightly heavier mix that holds more moisture, a slightly larger pot, and added background nutrition in the mix means my transplants can go a day or several without me fussing over them. I do still believe that a sterile mix is a probably a good idea for seed starting, though I have not seen any problems when using not-sterile vermicompost.
LED grow lamps are generally very expensive and are probably overkill for getting a little broccoli up and going. Both these types of lamps are mostly designed for professionals who want to take a crop through it&#;s full life cycle indoors or in a greenhouse with precise levels of supplemental light &#; a much more demanding lighting task than growing stocky, well-rooted transplants for outdoor growing.
There is one cash crop whose value probably justifies the expense of these kind of lights (::cough::pot::cough::) and I don&#;t grow it. Homebrew Husband and I are closely watching LED grow light technology. We think in a couple years the startup cost of this technology and the diversity of options for hobbyist set-ups will be where it needs to be for us to make the leap from our old, crappy fluorescents.
Update: LED lights have come down in price radically since I first published this post, and have always held the advantage in long-term operating costs. We are trialing value-priced LED lighting this spring to see if the performance and durability matches our T5 fluorescents. If it is, my recommendation will be for gardeners to start their seedlings under LED grow lights.
I hate, hate hate those pop-up, peat/coir, seed-starting pucks. Some people love them. If you look on the Amazon reviews, apparently most people love them. Count me as not among those people.
First, they are typically too small for all but the smallest transplants (like lettuce or chard). The mesh that surrounds the peat may, in some theoretical sense, be biodegradable but it certainly doesn&#;t break down quickly &#; I was finding those mesh liners in my raised beds for three years after I swore off the peat pellets forever.
What peat pellets are really good for is air pruning roots to encourage a well-branched root system at transplant. Soil blocks give you the same advantage without the mesh, and are less expensive in the long run. Or, recycle old newspapers into really biodegradable seed starting pots.
Propagation domes are the clear plastic lids you put over your seed propagation tray to keep humidity and moisture in and stop the potting mix from drying out while seeds are germinating. You know what works just as well? A plastic bag or a sheet of plastic wrap.
I have used propagation domes, and I find them flimsy unitaskers, for the most part. As soon as seeds start popping up, take any covering off your seeds or risk mold and damping-off disease in your seedlings. Exception: if you are rooting cuttings, prop lids might be great for you.
What do you think &#; what are your favorite seed starting tools and toys? What&#;s worth it to you, and what isn&#;t?
I've been gardening and writing about gardening for more than 20 years, yet I find I'm always learning new things about the plants, insects and other critters that call my backyard home. That's the great thing about gardening &#; it's never boring! I've worked as a landscaper, on an organic farm, as a research technician in a plant pathology lab and ran a small cut-flower business, all of which inform my garden writing. Someone once asked me when I'll be finished with my gardens, to which I replied, "Never!" For me, gardening is a process, not a goal.
Whether you're new to starting seeds or looking for fresh ways to grow your healthiest plants, we have supplies and systems that ensure success. With so many choices, how do you decide which is right for you? We're here to help.
Although you can start seeds in just about any container as long as it has holes for drainage, as with any task you're more likely to have better success using equipment designed specially for that purpose. And if you're new to seed-starting or introducing a friend to growing from seed, why not start with the systems that ensure success? Here are some considerations to help you choose.
Reusable pots and trays are made from durable materials that can be washed, sanitized, and reused year after year.
Plantable pots are made from biodegradable materials so the seedlings can be set in the garden pot and all, eliminating root disturbance. Cleanup is easy, and there are no bulky pots to store.
DIY pots includes those made from recycled materials, such as newspapers, as well as pot-free soil blocks.
Deep-root pots encourage more extensive and robust root systems that help plants make an easy transition to the garden.
Self-watering systems deliver water to seedlings as they need it, reducing the risk of over- or under-watering.
High volume systems allow you to grow a garden's worth of seedlings in a compact space.
This innovative self-watering seed starting system is 30% deeper than our Deep Root, growing full-size, garden-ready seedlings that are hardier and healthier. Optional add-ons, sold separately, include: additional Seed Starting Trays and Humidity Domes for fast germination.
Self-watering system extends time between waterings
Durable, reusable & dishwasher-safe
Large pop-out hole in each cell makes transplanting easier
Perfect for:
peppers, zinnias, and other seedlings that would benefit from a BIG starting space; no need to transplant up in a larger pot!
All the benefits of our original XL Seed Starting Kit, but made with hemp fiber and 25% less plastic! Grow extra-large seedlings with an extra-green self-watering seed starting system. Additional Seed Starting Trays and Humidity Domes for fast germination, sold separately.
Made with hemp fiber and 25% less plastic &#; each kit keeps nearly 3 pounds of CO2 out of the atmosphere!
Self-watering system extends time between waterings
Durable, reusable & dishwasher-safe
Large pop-out hole in each cell makes transplanting easier
Perfect for:
peppers, zinnias, and other seedlings that would benefit from a BIG starting space; no need to transplant up in a larger pot!
This heavy-duty, recycled-plastic seed starter includes an efficient and effective self-watering system that solves the challenges of over- or under-watering. Simply fill the reservoir and plants get the water they need, when they need it.
Capilary mat delivers water from reservoir to soil
Dishwasher-safe for easy sterilization between uses
Clear cover holds in heat and moisture to maximize seed germination
Perfect for:
the brand new gardener. The included humidity dome helps seeds germinate and a bottom-up watering design will support veggies, herbs, and flowers
Expandable paper honeycomb creates a whopping 50 cells. When you're ready to transplant into the garden, pots tear apart so you can plant them, paper liner and all.
Plantable pots are biodegradable and minimize transplant shock
Ideal for high-volume growing
Reusable perforated tray; paper cell refills available
Perfect for:
cucumbers, sunflowers, and other seedlings that don&#;t like being handled due to transplant shock
The ultimate in upcycling! In seconds you can transform strips of newspaper into seed-starting pots, ready to nestle into a waterproof tray and fill with soil mix. Easy, fun, and economical for high-volume growing.
Biodegradable pots minimize transplant shock
Make as few or as many as you need
Eliminates the clutter and storage hassles of plastic pots
Perfect for:
radishes and other quick-growing seeds that don't need to spend weeks in a seedling-sized pot
These fully biodegradable pots ease transplanting woes and work, allowing you to plant directly into the garden &#; pot and all. The wood fibers immediately begin to biodegrade, ensuring adequate moisture and aeration as well as restriction-free root growth.
Plantable pots transplant directly into the soil
Heavy-duty plastic tray is reusable year after year
Suitable for organic gardening! No binders or glue in the pots.
Additional biodegradable seed trays sold separately
Perfect for:
cucumbers, nasturtium, squash, and other seedlings that grow quickly and do not appreciate having their roots disturbed
An ingenious farmer makes these transplanting pots from odor-free, 100% composted cow manure. As your seedlings grow, the pots gradually degrade, releasing organic nutrients. Plant pot and all in the garden for healthy root growth without transplant shock.
Biodegradable pots transplant directly into garden
Roots grow through and take natural fertilizer with them
Eliminates transplant shock
Perfect for:
heavy feeders&#; like tomatoes, squash, and broccoli will appreciate the slow release of nutrients as this manure-based pot degrades.
Never run out of starter pots again! This clever device presses moistened soil into compact blocks with a small divot in the top, ready for dropping in a seed. Roots grow freely, get oxygenated, and grow more robustly as a result.
Make blocks as you need them &#; no need to store plastic pots
An easy, no-waste, DIY solution that's perfect for high-volume growing
Minimizes transplant shock.
Perfect for:
peppers, tomatoes, and other seeds that would benefit from a BIG starting space; no need to plant up in a larger pot!
An attractive seed starter worthy of display on a tabletop or under lights. The leakproof tray holds 24 individual, tapered cells, so you can bring the ready-to-transplant seedlings to the garden without disturbing the other plants.
Longlasting and resuable, year after year
Want more information on Leak-Proof Seedling Trays? Feel free to contact us.
Chic galvanized metal complements home decor
Seedlings remove easily with little root disturbance
Perfect for:
starting a variety of seed types; separate pots make it easy to transplant individual plants one at a time
This self-watering system features deep growing cells that result in more root mass &#; the secret to vigorous seedlings that thrive when transplanted. The smart design is inspired by the systems used in European horticulture laboratories.
Heavy-duty system can be reused for many years
Self-watering system ensures proper hydration
Perfect for:
peppers, tomatoes, zinnias, and other seeds that would benefit from a BIG starting space with plenty of root space
Pop-Out Pots are the secret to seedlings that are primed for robust growth in the garden. Transplant young seedlings from seed starting trays into these self-watering pots. When it&#;s time to set plants in the garden, simply lift the fabric strips to &#;pop out&#; plants without disturbing roots.
Self-watering system ensures perfect hydration
Easy-lift line minimizes root disturbance
Compact design fits on a windowsill
Perfect for:
cucumbers, squash, sunflowers, and other seedlings that don&#;t like being handled due to transplant shock
We designed this system for season after season of successful seed-starting. The leak proof tray holds 24 individual cells, so you can bring the ready-to-transplant seedlings to the garden without disturbing seedlings that aren't quite big enough.
Enjoy seed-starting success year after year
Tapered pots let you easily remove seedlings
Wire grid with moisture-retaining mat keeps seedlings hydrated
Perfect for:
starting a variety of seed types; separate pots make it easy to transplant individual plants one at a time
These sustainable silicone seed-starting trays are durable, reusable, and easy on tender young roots. Because they're so flexible, you can pop seedlings out with ease &#; no tugging or tearing required.
Pop seedlings out quickly and easily
BPA-free, food-grade silicone
Dishwasher safe
Perfect for:
starting seeds with kids (crush-proof!) or gardening in colder climates (frost-proof!)
These silicone trays make seed-starting so much more fun! Like other systems they have base drainage so that soil doesn't stay soggy and rot your seeds. Unlike plastic trays, they won't snap, crack, or break from use. Plus, they're flexible and twistable &#; so when seedlings are big enough to go out to the garden, it's super easy to pop them out. Use 5 to a base tray and you have 50 plants in a 10" x 20" space!
Durable and flexible
Reduces risk of transplant shock
5 trays fit perfectly in our Heavy Duty planting tray
Perfect for:
starting A LOT of seeds with kids (crush-proof!) or gardening in colder climates (frost-proof!)
You'll love this reusable, no-mess seed-starting system. Just hydrate the 50 individual coir discs in their cells, add your seeds, and wait for the little shoots to appear! Water as needed until they're ready to transplant into the garden, coir and all! Replacement coir discs available separately.
No soil to mix or scoop
Start a lot of seeds in a small space
Perfect for:
s
tarting a whole garden; 50 pre-fi
lled cells make it easy to start many, many seeds at once
Whether you&#;re a seed starting beginner or a long-time grower experiencing new challenges, you&#;re not alone! We&#;ve collected some of the most common questions we get asked about seed starting with helpful answers and troubleshooting advice.
Finding the right seed starting system is only half the battle! Explore our deep dive on seed-starting to learn the ins and outs of growing flowers and veggies from seed, so you can graduate from novice sower to master grower!
To get the hang of seed starting, it takes practice. There is a lot to know and a lot to get right, including watering, lighting and timing. So in this week&#;s podcast, I am answering seed starting questions that listeners have submitted to help you have a successful seed starting experience and get over any hurdles you&#;ve confronted.
Last week, I discussed the five most common seed starting mistakes, a list that I came up with based on the 5,000 or so questions that I have fielded from the Online Gardening Academy&#; Master Seed Starting course over the past three years. I set aside this week to answer the questions you still had after listening to last week&#;s roundup of common mistakes.
Master Seed Starting is now entering year four. The enrollment period runs through Monday, January 29, at which point the launch window closes until next year. It&#;s a comprehensive course with 75 instructional videos. It took two years to create this course, with trials and experiments that I documented to craft the many hours of course content.
You can also register right now for my free webinar Seed Basics & Beyond: 9 Things to Know Before You Start Plants From Seed. Three opportunities remain to attend, one per day from January 25 to 27. This webinar is full of information to help you take your seed starting to the next level. In this webinar, I share what you need to know about seeds to understand how they work so that you can be more successful in your seed starting endeavors. I firmly believe that the more that you understand about working with seeds and what they need to be successful, the more success you will have.
You can delve further into seed starting by checking out the many &#;joegardener® Show&#; podcast episodes and joegardenerTV YouTube videos I have made on the topic. My video &#;How I Start Seeds Indoors Tips & Techniques&#; is a great place to start. In 15 minutes I take you through my entire process for sowing seeds indoors, from putting them into the cell trays and watering them in after sowing the seeds, to taking them down to my seed starting room and putting them under the lights. For even more, see the Links & Resources section at the bottom of this page.
Check Seeds for Viability
One of the most important things to know when seed starting is whether your seeds are still good. If they were not packaged for the current year (this date should be on the seed packet) they may no longer be viable. The older they are, the greater the chance that the seeds will be duds, so fresh seed is the way to go if you don&#;t want to take any chances.
Some seed varieties, such as lettuce, go bad quickly, while others, such as tomatoes, can last for years if stored well. If you have older seeds that you are unsure about, you can conduct a simple viability test. Take out 10 seeds and put them onto a damp paper towel, and fold the paper towel over a few times. Put the paper towel into a zip-lock bag and set the bag someplace warm &#; around 70°F. Three to five days later, check for seed germination. Did seven seeds sprout? Your seeds have a germination rate of about 70%. Did one sprout? Your seeds have 10% viability.
If you discover that the seeds you saved have 50% viability, you should sow them at a density of two per cell so that you can expect one sprout per cell.
Extending the Viability of Seeds
Moisture and heat are the enemies of maintaining the viability of seeds. Dry and cool are the best conditions for seeds to ensure they last.
When saving seeds, ensure they are dry before putting them into storage, and add a silica pack or two to each seed envelope to absorb any lingering moisture. (You can find all of my seed saving and seed starting supplies and equipment at my Amazon shop.)
A good rule of seed storage is to never go over 100. Take the average temperature in the room and the average humidity and add them up. For instance, a 70° room with 30% humidity adds up to 100, and that will be safe for stored seeds. But if the temperature is 70° and the average humidity is 40°, now the total is 110, and that won&#;t be good for the long-term viability of your saved seeds.
Seed Starting Mix
Most seed starting mixes that consumers can find at big box stores do not include a wetting agent. Also known as a surfactant, a wetting agent is described as something that makes water wetter. It breaks the surface tension of water so the seed starting mix can readily absorb the water.
Wetting agents are found in mixes available to the nursery trade, but probably not in the bag of seed starting mix you brought home. You may find that when you add water, the water just sits on the top of the mix. That&#;s because the mix is hydrophobic. Peat moss is notorious for this. Once peat moss is wet it holds water very well, but when dry it is difficult to get it to absorb any water.
I use a professional seed starting mix, Pro-Mix BX, which comes with a wetting agent. The water soaks in immediately, which avoids the tedium of patiently soaking straight peat moss by adding a little bit of water at a time and waiting.
I use the shower nozzle of my kitchen sink on a light spray, and the water goes right into the seed starting mix with a wetting agent. If your mix is not absorbing water well, you can gradually add a little bit of water at a time, a couple minutes between applications, for about 20 minutes. Alternatively, you can premoisten the mix prior to adding it to your seed trays and sowing seeds. And once your seeds are sown, you can top the seeds off with a little more premoistened mix and sprinkle more water on top. Because the mix is presoaked, it will accept this additional water readily.
When watering newly sown seeds, take care not to blast the mix with a sharp stream of water. The seeds may float right out of the tray or into other cells. But when you practice, you&#;ll get a feel for this quickly.
PittMoss
Lori Jo Jamieson asks about using PittMoss for seed starting. I have used this product for several years now, and the more I use it the better I get at seed starting with it.
PittMoss is a non-peat, non-coir alternative for seed starting. It&#;s made of recycled paper and cardboard that&#;s been engineered to mimic soil. It&#;s very finely ground but still a little bit chunky. It looks and feels very different than peat moss or coir, but it is an alternative that has promise.
I am currently experimenting with 2-inch-deep cell trays filled with 100% PittMoss that I am comparing to trays that use a mix of PittMoss and peat moss or PittMoss and coir.
When I spoke about PittMoss with Dr. Charles Bethke, the manufacturer&#;s horticultural soil and nutrition consultant, he said that PittMoss is really designed for 4-inch-deep trays, because shallow trays tend to get waterlogged since they don&#;t have the depth of gravity to move excess water out.
Figuring out how to use 2-inch trays with PittMoss took me some time. It is a different experience than sowing into peat moss or coir, and there is a learning curve there.
The Best Humidity Domes
Heather C. asked about using humidity domes over seed starting trays. These range from 2 inches high to 7 inches or even taller. I am a firm believer in using 2-inch domes. If you are challenged for space overhead, you don&#;t want tall domes. A tall dome will make it difficult to adjust the distance of your lights from your plants. The 2-inch domes also cost less, which is another plus.
A shallow dome over the seedbed will more effectively hold moisture in the seed starting mix. A taller dome gives the humidity more room to spread out, which can lead to the seed starting mix drying out on its surface.
I use the taller domes for propagating cuttings. That&#;s when I find I need more than 2 inches of head space.
Heat Mats: Nice to Have
I put heat mats, also known as propagation mats or seed starting mats, in the category of &#;nice to have&#; but not &#;need to have.&#;
Seeds have a preferred temperature range in which they will germinate. The range is different from one seed variety to the next, and if the soil is either too cold or too hot beyond the range, the seeds are not going to germinate. If your seed starting room is cooler than that range, a heat mat will help get the soil temperature where it needs to be. You can even buy a mat with a thermostat to dial the mat into a specific temperature.
I use heat mats all the time for my warm-season crops, especially tomatoes and peppers.
Once the seeds germinate, the heat mat should be turned off. Leaving the heat mat on too long can create an adverse reaction. Cool soil is better for root development, and the air temperature is more important than the soil temperature at this point.
How to Know Your Moisture Is Correct
A good way to know if your seed starting mix is moist enough is to compare the dry weight of the mix to its weight when it has reached field capacity, which is as much water as it can hold. Aim for a moisture level, and weight, about halfway between totally dry and field capacity.
If sewing in soil blocks, you won&#;t know the dry weight because you are starting with moist mix pressed into blocks. Soil blocks inherently dry out faster than mix in plastic cells because soil blocks are exposed on all sides. You may not know how light the blocks are when completely dry, but you can still get a sense of how dry the blocks are based on their weight. You can also get a better sense visually of whether soil blocks are dry, compared to looking at seed starting mix in cells, where you can only see if the top is dry.
You can also reach in and tap a block. If it feels hard and crusty without a lot of give, your blocks need water.
I don&#;t bottom water soil blocks because it is hard to know if all of the blocks are getting water. The blocks on the outside of the trays could suck up all the water, leaving the blocks in the middle dry.
I water soil blocks from the top using a narrow spouted watering can to precisely direct water. If you use a floret that has more of a shower spray, you risk the water beating down the tender seedlings. With a narrow spout, you can get water where it needs to be without pummeling the seedlings.
Lighting
Grow lights come in full-spectrum types and dual-band lights. Full spectrum lights are white light, and dual-band lights emit a purple hue &#; I call it burple &#; which is a combination of the blue light frequency and the red light frequency. The red and the blue light frequencies do the most to promote the growth of the plants.
The problem with dual-band lights is that purple-ish look is not a pleasing look. If you have to deal with it every day in your office or living room, it&#;s annoying. Though dual-band lights are the most effective grow lights, it doesn&#;t make enough of a difference to justify putting up with the unattractive and unpleasant burple light. So I only use full-spectrum lights; it&#;s just easier on the eyes.
If you will keep your grow lights someplace where they are always out of sight, dual-band lights could be the way to go for you.
Fertilizer
Do you need to fertilize seedlings when starting seeds in soilless mix that is free of fertilizer? There is a great debate about this, but I can tell you that I personally rarely fertilize my seedlings between the time they are sown and when they are transplanted outdoors.
Some seed starting mixes contain a trace amount of fertilizer, known as a &#;charger,&#; to give seedlings a tiny kickstart. I use these mixes sometimes, but the fertilizer does not last.
Occasionally, as I pot up seedlings to larger containers, I add a light dose of fish emulsion fertilizer or something else with an NPK ratio of around 2-3-1.
You shouldn&#;t feel like you need to add fertilizer. The seed embryo &#; the material inside the seed coat &#; has the food that the seed needs to germinate and grow to the point that it&#;s on its own. First the seed leaves (cotyledons) develop to start the photosynthesis process, and then the true leaves come on. At this point, the plants create their own food using the light emitted by your grow lights.
I generally don&#;t add fertilizer when seedlings near the time they are going to be moved outside because I&#;m not entering them into a beauty pageant or state fair where they have to look tremendous or perfect. I know once they are planted outside in true soil, natural sunlight and good rainwater, they will be fine &#; and they&#;ll take off. They will make up for any lost time when they didn&#;t get any supplemental nutrients.
If you still feel the need to fertilize, use an organic fertilizer solution that has a low NPK ratio and dilute it to a quarter or half of what the bottle recommends. (If it says 1 part solution to 10 parts water, add at least 20 parts water). The worst thing you can do is overdo it on fertilizer when plants are still indoors. Stimulating growth in that artificial environment will lead to plants that don&#;t have sufficient space for root growth and top growth, and your lights probably won&#;t meet the demands of the larger plant.
Why Cool Season Crops Are Started in the Summertime
Cynthia Scott writes from Florida, where for much of the year it&#;s hotter than most U.S. gardeners are accustomed to. She asks about starting cool season crops and why the seeds are started in the middle of the summer.
The reason cool season crops are started when temperatures are still high is because there needs to be sufficient time for the crops to mature before the days get too short and everything stops growing as much. And for those living in cooler climates, the first frost date of fall is another concern. When it is too cold, the growth of cool season crops will be hindered, and they will eventually die in a freeze.
The only way to ensure plants mature in time to beat shorter days and the first freeze is to start them early. Cool season crops have no issue, for the most part, getting started when temperatures are warm or even hot. What&#;s important is that they mature in cool weather, so they don&#;t bolt and become bitter.
Cool season crops can germinate in soil that is up to around 85°F, depending on the variety. Even in an un-air-conditioned home, soilless mix that is kept consistently moist should be under this top-end of the range.
When it comes time to plant the crops outside but it is still blazing hot, you need to provide some relief. You can do this with shade cloth. Suspend the shade cloth up high to leave lots of airflow between the plants and the cloth, so no heat is trapped. This could knock the temperature down by up to 10°, depending on what percentage of shade cloth you use. It will take some trial and error to figure out what is sufficient.
Keep the soil mulched so it stays cooler, and keep drip irrigation or soaker hoses under the mulch to maintain soil moisture.
For those in Florida and warm climates, I recommend starting cool season crops indoors rather than direct sowing. Your house is hopefully cooler in summer than the temperature outside.
If you haven&#;t listened to my answers to listeners&#; seed starting questions, you can do so now by scrolling to the top of the page and clicking the Play icon in the green bar under the page title.
What seed starting questions do you still have? Let us know in the comments below.
Links & Resources
Some product links in this guide are affiliate links. See full disclosure below.
Episode 037: Starting Seeds Indoors: The Non-Negotiables for Success, Pt 1
Episode 038: How to Start Seeds Indoors: The Non-Negotiables for Success, Pt. 2
Episode 039: How to Start Seeds Indoors: Digging Deeper, Pt. 3
Episode 083: Gardening Indoors: The Science of Light, with Leslie Halleck
Episode 125: Saving Seeds: The Basics, the Benefits and Beyond
Episode 238: Peat Moss: Examining the Challenges of Its Ongoing Use in the Face of Climate Change
Episode 256: The Challenge (and Solution) for Using Coconut Coir as a Seed Starting and Growing Medium
Episode 259: Getting to Know PittMoss, a Peat-free Growing Medium Alternative, with Dr. Charles Bethke
Episode 297: Seed Starting Essentials
Episode 348: The Top Five Seed Starting Mistakes and How to Fix Them
joegardener blog: The Best Soil Temperature for Seed Germination
joegardener Seed Inventory Chart & Seed Longevity Chart
joegardenerTV YouTube: How to Know if Seeds Are Still Good
joegardenerTV YouTube: How I Start Seeds Indoors Tips & Techniques
joegardenerTV YouTube: How to Save Tomato Seeds
joegardener Online Gardening Academy&#;: Popular courses on gardening fundamentals; managing pests, diseases & weeds; seed starting and more.
joegardener Online Gardening Academy Organic Vegetable Gardening: My new premium online course. The course is designed to be a comprehensive guide to starting, growing, nurturing and harvesting your favorite vegetables, no matter what you love to eat, no matter where you live, no matter your level of gardening experience.
joegardener Online Gardening Academy Master Seed Starting: Everything you need to know to start your own plants from seed &#; indoors and out. Open for enrollment through Monday, January 29.
joegardener Online Gardening Academy Beginning Gardener Fundamentals: Essential principles to know to create a thriving garden.
joegardener Online Gardening Academy Growing Epic Tomatoes: Learn how to grow epic tomatoes with Joe Lamp&#;l and Craig LeHoullier.
joegardener Online Gardening Academy Master Pests, Diseases & Weeds: Learn the proactive steps to take to manage pests, diseases and weeds for a more successful garden with a lot less frustration. Just $47 for lifetime access!
joegardener Online Gardening Academy Perfect Soil Recipe Master Class: Learn how to create the perfect soil environment for thriving plants.
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Disclosure: Some product links in this guide are affiliate links, which means we get a commission if you purchase. However, none of the prices of these resources have been increased to compensate us, and compensation is not an influencing factor on their inclusion here. The selection of all items featured in this post and podcast was based solely on merit and in no way influenced by any affiliate or financial incentive, or contractual relationship. At the time of this writing, Joe Lamp&#;l has professional relationships with the following companies who may have products included in this post and podcast: Corona Tools, Milorganite, Soil3, Greenhouse Megastore, Territorial Seed Company, Earth&#;s Ally, Proven Winners ColorChoice and Dramm. These companies are either Brand Partners of joegardener.com and/or advertise on our website. However, we receive no additional compensation from the sales or promotion of their product through this guide. The inclusion of any products mentioned within this post is entirely independent and exclusive of any relationship.
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