WHAT PROPAGATION TRAY IS BEST FOR YOU?
Thebest size cell plug seed traysfor you to choose will be dependent on a few factors. We will go over the different options to help you select the best for you. Consider first, what is your intent in seed starting?
What size cell tray should I use?
Quickly review some of these seed starting questions.
Are you growing a large number of one variety of plants for transplanting row crops?
Are you planting smaller numbers of a wide variety of plants?
Will you be planting your crops all at once, or will you be using the succession planting method?
What type of seeds will you be planting? Peppers, tomatoes, lettuce, watermelon, etc.?
How large are the seeds?
How long will your seedlings need to stay in the cell trays?
Will you be potting up your plant starts or planting out directly from the plug trays?
How much protected growing space do you have to start seeds in?
Will you use a heat mat or rely on ambient temperatures for germination?
Check outHow to Size and Use Cell Insert Propagation Traysvideo for a look at how these trays are commonly used.
What size cell seed trays should I use?
The best plug trays for home gardens.
32 Cell Seed Starting Trays
The32 cell plug propagation tray insertsare the largest cell seed starting tray size that Bootstrap Farmer carries., measuring 2" x 2". The larger size makes them perfect for canopy development of crops.
These cell seed tray inserts can be used in two ways. Directly plant into these cell inserts with deep drainage holes with Rockwool cubes, soilless media, or soil mediums. The entire tray can be bottom watered using a1020 shallow tray with no holes.
Another way these insert trays are used is as a holder for these seed-starting pots.Seamlessly designed to sit in a 1020 shallow tray with no holes, the insert will hold 32 of these2.5" pots, keeping them from tipping over in a 1020 trays and making quick work of transporting them out to the garden space. The individual seed cup style is very popular for school and community projects as these can go from seed to transplant without needing up-potting in between and come inbright colors!
Recommended Plants: Tomatoes, Melons, Cucumbers, Pumpkins, Squash, Peppers and other large-seeded crops
50 Cell Seed Starter Trays
These50 cell propagation traysare a happy medium of saving you space in your seed starting area while still being able to plant a large number of seedlings like lettuce that will be directly transplanted. Because the 50 cell tray has a much larger soil volume than the 72 cell plug trays or 128 cell trays, you will have a bit more wiggle room when you need to transplant for optimal root growth. Plants grown in these trays will be less likely to become root-bound if unsettled Spring weather delays your planting. This size also allows for canopy development of the seedling.
If you know that your seedlings will need to be potted up before they are ready to move outside, you will want to select one of the cell trays listed below or plan on potting up into larger pots like our new 5 inch grow pots with carrier.
Plastictrays of this size are great for planting early greens and brassica crops like broccoli and collard greens for the home garden. Just be sure that if you choose to mix varieties in one cell tray, they all have similar germination times and time to transplant.
Recommended Plants: Lettuce, brassicas, cucumbers, slow-growing flowers, and herbs.
The Best Cell Plug Tray Size for Large Scale Market Gardens
72 Cell Plug Seedling Trays & 72 Cell Air Prune Trays
The72 Cell traysare the most popular choice amongst market gardeners. They are a good balance between space for growing and seedlings per tray. Each cell is 1.5" square and 2.25" deep, making them an excellent option for a large variety of plants. Theseplastic trays are also a good choice for vine plants. However, you will want to transplant the vine plants earlier than you would with the 32 Cell trays to prevent root bound seedlings. This cell plug tray is designed to use a heavy-duty1020 deep trayfor easy bottom-watering.
For optimal air pruning and extremely happy plants, we recommend our 72 air prune trays. All the benefits of soil blocking without the mess!
Recommended Plants: Sunflowers, Early Season Peppers, Early Season Vine Crops, Early Season Cole Crops (Cabbage, Cauliflower, Collards, Kale, Mustard, Kohlrabi, Broccoli, Brussels sprout, Watercress)
128 CELL TRAYS
These128 Cell Traysare a great choice if you wish to start row crops or many baby greens. This configuration is ideal for starting many seeds but is not meant for crops that need more than a few weeks. Each cell is 1" square and 2.25" deep. You will be able to plant 78% more seedlings with one tray than the more common 72 cell seed starter trays. These 128seed trays are compatible with theheavy-duty 1020 deep trayfor bottom watering. You will want to up-pot your seedlings from this size seed tray into a larger pot or grow bag if you do not plan to transplant outdoors for an extended period to prevent seedlings from becoming root-bound.
Recommended Plants: Lettuce, Herbs, Cole Crops (Cabbage, Cauliflower, Collards, Kale, Mustard, Kohlrabi, Broccoli, Brussels sprout, Watercress), Celery, Leeks, Flowers.
200 CELL TRAYS
These200 Cell Traysare excellent trays if you want to be economical about growing cole crops, lettuces, and other small-seeded crops. You will be able to grow ~2.8 times as many plants with one tray as you would with a 72 cell tray. Each cell is 0.75" square and 2.25" deep.
If you are using a 200 cell plastic trays to start seeds, you will need to transplant your seedlings at an earlier stage. Typically once they have one, at most two sets of true leaves. This plastic tray size is most frequently used by larger-scale farmers and those who intend to pot up their seedlings multiple times before moving outside. They can also be used to start plants going into hydroponic systems if you use a soilless media likecoco coirorProMix.
Recommended Plants: Lettuce and Brassica Crops (Cabbage, Cauliflower, Collards, Kale, Mustard, Kohlrabi, Broccoli, Brussels sprouts, Watercress), Small seeded flowers.
Common Questions About Planting in Cell Trays
Can I plant root crops in plug trays?
While some experienced farmers have successfully planted crops like beets and turnips in cellseed trays, it is not recommended unless your climate does not allow for the direct seeding of root crops. Carrots, parsnips, turnips, and beets rely heavily on their taproot. This long central root is responsible for much of the water uptake of these plants, and if the root is disturbed or damaged during the transplanting process, the plant will not thrive.
Can onions and leeks be planted in seed starting trays?
Yes, unlike other root crops, members of the allium family have congregate root structures. This means that they are much more tolerant of root disturbances during transplanting. It is common for growers to plant multiple small seeds per cell and tease them apart for later transplanting.
What are the advantages to starting seeds in cell trays vs. larger pots?
Starting seeds in cell trays, especially in the larger ones, gives the grower the advantage of being able to start more seedlings in their growing space. This is especially handy for row crops where the grower may want to plant 100 or more of each variety. Growing this many seedling starts in larger seed pots would take up way too much space. The other advantage is that you will waste less growing media starting out your seeds and then up-potting the successfully germinated starts into new pots.
Can you overwater seedlings in cell seed trays?
Yes. It is possible to overwater seedlings growing in cell trays. A common mistake growers make is to leave water in the bottom 1020 tray at all times. This will eliminate your seedling’s ability to get oxygen. Bottom-watering with a 1020 can be properly done by adding just enough water to allow the cell tray to evenly absorb it during the watering and no more. You want to discard the excess water as it will become stagnant and invite anaerobic bacteria to wreak havoc on your newly established seedlings.
How long can my plants stay in the cell tray?
Most seedlings can stay in cell traysfor at least 4 weeks. The larger the cell volume, the longer a plant can grow before it becomes root-bound. Plants grown in a 200 cell tray will typically need to be potted up or transplanted outside once they have a full set of true leaves. Plants grown in a 32-cell insert pot can be kept in protected conditions for 6-8 weeks.
Why are my transplants not growing?
If your seedlings have been in the plug tray for too long, they may become root-bound. If this happens, you will see a large number of roots circling the plug when you pull it out of the tray. Plants that have become root bound do not produce new roots easily and will often stay stunted.
Transplant shock can also cause your garden plants to be stunted and remain small throughout the growing season. For more on how to avoid transplant shock, check out ourSeed Starting 101 Guidefor advice on how to harden off your transplants.
Can I fix a root-bound seedling or plant?
If your seedlings become root bound before you have time to plant them, you can improve their chances with a bit of extra work at planting time. Once you have the plug removed from the cell tray, gently tap the bottom of the roots to loosen the soil and use your fingers to tease them apart. It is ok and even desirable to tear a few of the roots when you do this. Separating and tearing the roots will encourage the transplant to produce new side roots and prevent further root circling.
Be sure to share your seed starting successes with us onInstagramand tag us with questions you have about the process.
If you're new to seed starting, this foolproof beginner's guide to starting seeds indoors will take you step by step from seed to harvest, quickly and easily. You don't need any fancy gear or grow lights to get started, and you can even upcycle small containers to put your seeds in. All that's needed is a sunny window, a basic seed-starting mix, and something underneath your pots to catch drips.
Exactly as the title says — this is an easy, no-fail guide to indoor seed starting.
You don’t need to read any gardening books first. You don’t need any fancy equipment. You just need your seeds (these are the best garden seed catalogs that I order from every year) and a few basic supplies to get started.
Whether you have a dedicated vegetable bed in your backyard, or a cluster of containers on your patio, it all starts out the same way. You have to plant your seeds, and germinating seeds inside your home (where you have the most control) is the best way to do so, especially for seeds that are hard to start.
Starting seeds indoors is ideal if you want to get a head start on the season, or if the weather is still too hot or too cold to put anything in the ground.
Related: Find First and Last Frost Dates Accurately with This Custom Planting Calendar
This simple step-by-step tutorial will take you from seed to seedling with a minimum of fuss. Just the stuff you need to know, and none that you don’t. (But if you’re the really-need-to-know type, I’ve added footnotes at the end to explain why you’re doing what you’re doing.)
Disclosure: All products on this page are independently selected. If you buy from one of my links, I may earn a commission.
How to start seeds indoors: a step-by-step guide
Step 1: Gather your seed starting supplies.
- Seeds
- Seed starting pots or cell trays
- Plant markers
- Seed starting mix (homemade or store-bought)
- Seed tray with humidity dome (often called a 1020 plant tray or propagation tray, or use any DIY drainage tray with plastic wrap)
- Spray bottle or squirt bottle filled with water
If you’ve already made your recycled newspaper pots, you’re all set. If you’ll be using other seed starting pots or cell trays, make sure they’re clean.1
You can also repurpose household items into seed starting containers, like egg cartons, Dixie cups, and yogurt cups. Just wash them out and poke a few drainage holes in the bottom with a nail or an awl.
Step 2: Fill your pots or trays with seed starting mix.
Dump your seed starting mix into a large tub or bucket, pour in a generous amount of water, and stir it up with your hands or a trowel.
As the seed starting mix starts to absorb the moisture, add more water as needed. (This will take several minutes, as peat-based seed starting mixes are slow to absorb.) You want the mix to be uniformly damp, like wet sand.
Fill your seedling pots with this pre-moistened seed starting mix.2
Step 3: Sow your seeds.
Place two to four seeds on the surface of the seed starting mix, and gently press the seeds down so they’re nestled in nicely.
If your seeds are very small, like basil or mustard, you can leave them uncovered.3
If your seeds are larger (like beans or peas) or they require darkness to germinate (check the instructions on the seed packets), cover them with a layer of vermiculite or seed starting mix equal to their height, usually 1/4 inch to 1/2 inch.
Step 4: Label your newly planted seeds.
Label each pot. Trust me, you will never remember what you planted where, as most seedlings look the same at birth.
At this early stage, cheap plastic plant markers work very well and stay out of the way, so save your big and beautiful metal plant markers for the garden.
Step 5: Keep your seeds moist and warm.
Mist your seeds with water.4
Assemble your pots in a seed tray (or reuse a disposable aluminum roasting pan, a baking pan, even that plastic clamshell that your salad greens came in) and cover with a humidity dome (or just plain old plastic wrap).5
If your dome has vents, keep them open to help with air circulation during the sprouting period.
Now, you need to add heat. Since sunlight is not essential at this point, your seed trays can be placed wherever it’s warmest in your house, such as an attic, bathroom, laundry room, or kitchen.6
If your seedling pots stay covered in a warm nook, the low humidity will keep your seeds happy until they sprout. High humidity will make them sad. Only spritz the seeds with more water if the mix feels dry to the touch.7
Within a couple of days to a couple of weeks, the seeds will germinate. As your seedlings start to emerge, some of them will look like they’re wearing little seed hats.
Germination (the process of a seed sprouting) is highly variable, so don’t stress if it feels like it’s taking forever to happen. In most cases, seeds will germinate within three weeks (after that, try starting a new round of seeds).
Step 6: Give your new seedlings light.
At this stage, the newly germinated seedlings need light. Remove the humidity dome or plastic wrap, and move the seedlings to the sunniest spot in your house (preferably a south-facing window).
Continue to keep the mix moist, but not overly wet. Seedlings should be watered once a day or every other day, depending on how much sun and heat they get.
Remember that seedling roots are fairly close to the surface and they’re growing in a small amount of media, so they don’t need a deep soak the way larger plants do.
I like using spray bottles or squirt bottles, as the gentle streams of water won’t displace seeds or damage seedlings.
Step 7: Moving day! Transplant the strongest seedlings when they’re ready.
After your seedlings develop their first “true set” of leaves, they are ready to be transplanted.8
If more than one seed sprouted, choose the strongest one and pinch or snip off the others. You can even keep all of them, but be careful separating the roots if the seedlings are close together.
Transplant the seedling into a larger container filled with potting mix. Hold it by the cotyledons (the first leaves that appear) and try not to manhandle the tiny roots.
At this stage, you can lightly drench the potting mix using a diluted solution of compost tea or all-purpose fertilizer. Keep it simple, keep it organic, and don’t obsess too much over the nutrients.9
Give the seedling plenty of sunlight each day (at least 12 to 16 hours is optimal for most vegetable seedlings) to avoid the “leggy” look. (Learn how to fix leggy seedlings if this is happening to you.)10
Step 8: Harden off those seedlings.
To get your seedling prepped for a good life outside, you can start to harden off the seedling11 by moving it outside under diffused light for a few hours and bringing it back inside each night.
Over the next week, move it from diffused sun to partial sun to full sun, and for longer periods of time, until it’s finally kept outside all night.
Step 9: Transplant your seedlings outdoors.
After the hardening off period, you can transplant your seedling to its final destination, whether straight into your garden or into a larger container.
And then, in a couple of months, you can enjoy the fruits (and veggies) of your loving labor!
More Ways to Start Seeds Indoors
There's more than one way to start your seeds and make sure they sprout!
Germinate Seeds Quickly With Coffee Filters or Paper Towels
Whether you're trying to start tricky seeds with long germination times, or find out if your old seeds are still viable, the coffee filter (or baggie) method is a quick and simple way to start many seeds at once in a small space.
How to Start Seeds in Eggshells, Save Money, and Have Fun
Save those cracked eggshells, upcycle your egg carton, and bookmark this indoor gardening DIY for a rainy day. Starting seeds in eggshells is a fun and easy project that kids will delight in helping with!
How to Soak Seeds to Speed Up Germination Time
If you've had trouble with seeds not sprouting, soaking them in water before you sow them can greatly increase their chances of germinating. This method works well with legumes, beets, squash, and other thick-shelled seeds.
How Long Do Seeds Last? (+ Cheat Sheet on Seed Expiration Dates)
How old is too old? All seeds have a shelf life, but their longevity depends on the quality and condition when you bought or saved them, and how they've been stored since. Find out whether you should keep or toss your seed stash.
1 This seems obvious, but laziness gets the best of us. Clean pots are key and help keep damping off at bay (an untreatable fungal disease that causes seedlings to suddenly keel over and die at the soil line).
Discard or thoroughly wash any pots that previously housed diseased plants. Avoid using leftover soil from the nursery container you brought home, as it might harbor weed seeds and bad bacteria.
If you have a healthy garden, you can skip washing your pots and simply dump out the dirt from your pots before using again.
I’ve put countless seed trays and humidity domes to the test over the years, and found these trays and domes to be the thickest and strongest on the market — they don’t bend, flex, or crack as easily as other brands, and can be reused for many seasons. back
2 It’s easier to start with pre-moistened mix, as peat-based mixes are harder to wet down uniformly if they dry out in pots. Although peat has a very high water-holding capacity once it’s wet, it actually repels water when it’s dry. Go figure.
If you’re not using homemade seed starting mix, this is a reputable brand that I like. You do not need anything fancy; seeds just need a basic mix of perlite, vermiculite, and peat moss (or coco coir) to germinate and grow into healthy seedlings. back
3 For certain varieties of plants, light will often speed up germination (the process of a plant sprouting from a seed). back
4 The moisture will help the seeds shed their protective coating and eventually sprout. back
5 This creates a greenhouse effect to keep your seeds moist and warm, the key to germination. Most annual vegetables germinate best in temperatures of 75°F to 90°F. A few, such as radish, will germinate at lower temperatures.
Seeds will sometimes sprout in less than ideal temperatures, but the germination period will be longer. back
6 I like to put my seed trays next to my heating vent on the floor. Some gardening guides suggest placing your tray on top of a refrigerator, but most appliances these days are energy-efficient and do not give off much heat. back
7 Too much water will make the seeds rot. If your makeshift greenhouse is looking a bit too wet inside, remove the cover or plastic wrap for a few hours during the warmest part of the day to allow air circulation. Mold is no good for seeds, either. back
8 The true leaves are actually the second set of leaves that appear; the first leaves that initially unfurl are not leaves at all, but cotyledons. These leaf-life structures are part of the embryo of the seed, and supply food to the seedling until its true leaves begin the process of photosynthesis. back
9 I like to use home-brewed compost tea or liquid sea kelp. No fertilizer is fine, too, especially if you start with good soil. I have grown healthy vegetables with no fertilizer through a whole season, and could barely keep up with the harvests. back
10 It sounds sexy, but it makes your seedling tall and weak as it channels its energy into straining for sunlight. I also like to gently run my hands across the top of my seedling to simulate a breeze; this slows down initial growth and strengthens the stem. A few brushes a day is all it needs. back
11 Hardening off is the process in which you gradually acclimate the seedling to its future environment outdoors… getting it acquainted with the breeze, the birds, and the bees. back
Continue to Content
The Beginner’s No-Fail Guide to Starting Seeds Indoors
If you're new to seed starting, this foolproof beginner's guide to starting seeds indoors will take you step by step from seed to harvest, quickly and easily.
Prep Time
15 minutes
Active Time
15 minutes
Total Time
30 minutes
Difficulty
Easy
Materials
- Seeds
- Seed starting pots or cell trays
- Plant markers
- Seed starting mix (homemade or store-bought)
- Seed tray with humidity dome (often called a 1020 plant tray or propagation tray, or use any DIY drainage tray with plastic wrap)
- Spray bottle or squirt bottle filled with water
Tools
- Large bucket or tub
- Trowel
Instructions
- Gather your seed starting supplies. Instead of seed starting pots, you can also use recycled newspaper pots, or repurpose household items into seed starting containers, like egg cartons, Dixie cups, and yogurt cups. Just wash them out and poke a few drainage holes in the bottom with a nail or an awl.
- Fill your pots or trays with seed starting mix. Dump your seed starting mix into a large tub or bucket, pour in a generous amount of water, and stir it up with your hands or a trowel.
As the seed starting mix starts to absorb the moisture, add more water as needed. (This will take several minutes, as peat-based seed starting mixes are slow to absorb.) You want the mix to be uniformly damp, like wet sand.
Fill your seedling pots with this pre-moistened seed starting mix.
- Sow your seeds. Place two to four seeds on the surface of the seed starting mix, and gently press the seeds down so they’re nestled in nicely.
If your seeds are very small, like basil or mustard, you can leave them uncovered.
If your seeds are larger (like beans or peas) or they require darkness to germinate (check the instructions on the seed packets), cover them with a layer of vermiculite or seed starting mix equal to their height, usually 1/4 inch to 1/2 inch.
- Label your newly planted seeds. Label each pot. At this early stage, cheap plastic plant markers work very well and stay out of the way, so save your big and beautiful metal plant markers for the garden.
- Keep your seeds moist and warm. Mist your seeds with water.
Assemble your pots in a seed tray (or reuse a disposable aluminum roasting pan, a baking pan, even that plastic clamshell that your salad greens came in) and cover with a humidity dome (or just plain old plastic wrap). If your dome has vents, keep them open to help with air circulation during the sprouting period.
Now, you need to add heat. Since sunlight is not essential at this point, your seed trays can be placed wherever it’s warmest in your house, such as an attic, bathroom, laundry room, or kitchen.
If your seedling pots stay covered in a warm nook, the low humidity will keep your seeds happy until they sprout. High humidity will make them sad. Only spritz the seeds with more water if the mix feels dry to the touch.
Within a couple of days to a couple of weeks, the seeds will germinate. Germination (the process of a seed sprouting) is highly variable, so don’t stress if it feels like it’s taking forever to happen. In most cases, seeds will germinate within three weeks (after that, try starting a new round of seeds).
- Give your new seedlings light. At this stage, the newly germinated seedlings need light. Remove the humidity dome or plastic wrap, and move the seedlings to the sunniest
spot in your house (preferably a south-facing window).Continue to keep the mix moist, but not overly wet. Seedlings should be watered once a day or every other day, depending on how much sun and heat they get. Remember that seedling roots are fairly close to the surface and they’re growing in a small amount of media, so they don’t need a deep soak the way larger plants do.
- Moving day! Transplant the strongest seedlings when they're ready. After your seedlings develop their first “true set” of leaves, they are ready to be transplanted.
If more than one seed sprouted, choose the strongest one and pinch or snip off the others. You can even keep all of them, but be careful separating the roots if the seedlings are close together.
Transplant the seedling into a larger container filled with potting mix. Hold it by the cotyledons (the first leaves that appear) and try not to manhandle the tiny roots.
At this stage, you can lightly drench the potting mix using a diluted solution of compost tea or all-purpose fertilizer.
Give the seedling plenty of sunlight each day (at least 12 to 16 hours is optimal for most vegetable seedlings) to avoid the “leggy” look. (Learn how to fix leggy seedlings if this is happening to you.)
- Harden off those seedlings. To get your seedling prepped for a good life outside, you can start to harden off the seedling by moving it outside under diffused light for a few hours and bringing it back inside each night.
Over the next week, move it from diffused sun to partial sun to full sun, and for longer periods of time, until it’s finally kept outside all night.
- Transplant your seedlings outdoors. After the hardening off period, you can transplant your seedling to its final destination, whether straight into your garden or into a larger
container.
Did you make this project?
Please leave a comment on the blog or share a photo on Instagram
What to know after your seeds germinate
This post updated from an article that originally appeared on March 19, 2011.
View the Web Stories on how to start seeds indoors.
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