The Ultimate Guide to Choosing planting tray large

WHAT PROPAGATION TRAY IS BEST FOR YOU?

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The best size cell plug seed trays for 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 out How to Size and Use Cell Insert Propagation Trays video for a look at how these trays are commonly used.

What size cell seed trays should I use for a Home Garden?

The best plug trays for home gardens.

4 Cell Seed Starting Trays

Our brand new larger 4-cell plug inserts are deeper for growing varieties of crops that need a little more room. Eight of these removable inserts fit in a Bootstrap Farmer 1020.

6 Cell Seed Starting Trays

Our  6 cell trays have large 5/8 inch drainage holes on the bottom making it easy to remove your plant starts. They also make use of air pruning technology with long vertical slits on all 4 sides to prevent root circling in your seedlings. For easy color coding and tracking or your starts we are super excited to also offer our 6-cell trays in 5 cheerful colors. These are great for gardeners who will be starting a small amount of lots of different varieties as you can remove each type as it is ready without disturbing all the other starts that are sharing its heavy-duty 1020 deep tray  bottom watering tray. 12 fit in each 1020 tray or 6 to a 1010 tray. 

Shop Bundles & Kits here.

32 Cell Seed Starting Trays

The 32 cell plug propagation tray inserts are 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 a 1020 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 these  2.5" 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 in bright colors and now in clear!

Recommended Plants:  Tomatoes, Melons, Cucumbers, Pumpkins, Squash, Peppers and other large-seeded crops

50 Cell Seed Starter Trays

These 50 cell propagation trays are 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. 

Plastic trays 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

The 72 Cell trays are 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. These plastic 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-duty 1020 deep tray for 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

These 128 Cell Trays are 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 128 seed trays are compatible with the heavy-duty 1020 deep tray for 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

These 200 Cell Trays are 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 like coco coir or ProMix.    

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 cell seed 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. 

Related: Easiest Way to Water Seedlings

How long can my plants stay in the cell tray?

Most seedlings can stay in cell trays for 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. Check out our 3.3" seed starting pots and 5" pots for up-potting starts or shop our seed starting bundles.

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 our Seed Starting 101 Guide for 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 on Instagram and tag us with questions you have about the process. 

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I think we can all agree options are good- but give us too many options to choose from and we can easily feel overwhelmed. And as a result we may find ourselves failing to make any sort of decision at all…

This is at least how I felt when I was just getting started growing flowers and was trying to decide on which seed starting trays to purchase.

I mean, no one wants to spend money only to find out later that they invested in the “wrong” trays…am I right?!

And so today, I’m hoping to put your mind at ease. In this blog, specifically-  I thought we’d discuss the pro’s and con’s to some of the different seed trays out there on the market.  I’m also going to share with you some of my favorite trays to use; and even give you some considerations to think about when you’re selecting your own trays.

So if you’re wanting to learn more- let’s go!

(Psst.. Want to skip the explanation and get right to the good stuff?! I got you covered, this tray is my absolute favorite for starting seeds; and truth be told, it’s the one tray I use most on my small flower farm)

Understanding Seed Trays:

Now in general, all seed trays serve the same sort of purpose- they hold your soil in place so that you can grow healthy transplants for your flower garden. 

By planting your seeds in a single tray, it makes it easier to treat your seedlings all the same as they’re in the same container. You can water the entire tray at once. You can transport your seedlings at once- you know, when it’s time to plant you just have to handle a single tray and bring it out to the garden with you.

For the most part, all of the seed trays that you will encounter, they have the same overall length and width. And they can typically all fit inside a standard 1020 bottom watering tray. 

The biggest difference among trays is really found with the number of cells they contain.

The Importance of Cell Size in Seed Starting Trays:

Cell counts vary widely in trays and you can commonly find trays that have 32-cells, 50, 72, all the way up to 128, 288 and beyond.

Now, the more cells in a single tray- the smaller each individual cell will be. So for example, the cells of a 50 cell tray will be larger than those in this 72 cell tray.

Choosing which cell count to use is based partly on preference and how much room you have available to seed start. And then it’s based partly on the needs of the seeds you’re growing.

You see, the size of a cell limits the growth of a seedling. Smaller cells leave less space for seedlings to grow.

Ideally we want to give the seedling as much room as it needs to expand its roots and put on top growth so that it really thrives before we put it out in our garden.

During the growing process, if your seedling runs out of room to grow, generally, what happens is that the seedling becomes root bound. When this happens, the roots of your seedling become so entangled that they have a hard time absorbing nutrients from the soil.

Now some seedlings can bounce back after becoming root bound but it’s better if we can prevent this altogether as root bound plants can experience stunted growth, delayed flowering, or in extreme conditions, they can just flat out not survive.

Understand that the purpose of seed starting is to produce a robust plant start. So giving our seedling the proper amount of room to grow is important. 

Like I said, in an ideal situation we’d give our plants as much room as possible. But for a lot of us who grow seedlings on any kind of scale, the problem is that we often don’t have unlimited space.

I have a number of wired shelves where I grow all my plant starts. The shelves are 4 feet wide and so on one shelf I can fit 4 trays. 

If I’m growing my seedlings in 32 cell trays that means one shelf can hold a grand total of 128  seedlings. You know, 4 trays times 32 cells.

Now compare that to if I were growing my seedlings in 72 cell trays. Suddenly that same amount of real estate on my wire shelf is enough to grow 288 seedlings- more than doubling the amount of seedlings I’m able to grow in the same amount of space.

Can you see how it’s a fine balance between maximizing the space you have available so that you can grow as many seedlings as possible with also doing what’s best for the health of your seedling?

Best Seed Tray Recommendation for Flower Farmers:

For me, the 72 cell tray (with a few exceptions) is sort of the compromise between these two factors that I just mentioned. The reason that I often encourage new growers to start with the 72 cell tray is that for most flower varieties, the 72 cell is sufficient space for a seed to grow into a large and bulky enough plant start without requiring you to repot it before it’s time to to transplant into the garden.

And if I’m being really specific, my absolute favorite seed starting tray is the 72 cell seed tray that comes from Bootstrap Farmer. I believe that I’ve shared in past YouTube videos how I stumbled across the Bootstrap Farmer brand- but 5 seasons into growing flowers, I can honestly say that I haven’t found a tray that compares in strength and quality to this tray.

Even full of soil the Bootstrap Farmer trays don’t buckle- they’re a really durable tray and for me, it’s worth it to spend the extra dollar or two per tray because I know that I won’t need to replace them near as often.

So let’s discuss some instances when I would choose to use a different tray.

Seed Starting Trays for Specific Circumstances:

128-Cell (and smaller) Seed Starting Tray

If you’re struggling with germination with some of your seeds- tools like heat mats and humidity domes can be useful in helping you achieve those ideal situations for your seeds to germinate.

While I look at my equipment as a necessary investment in my business- sometimes you just don’t have the extra money to spend so that every tray has its own heat mat and humidity dome.

And so one of the ways around this may be to use a smaller-cell tray to start with. A 128 cell tray is great because you can start a good number of seeds in a small space- and this single tray fits nicely on heat mat.

In my experience, you just have to be careful that you’re monitoring your 128 and smaller cell trays to make sure that they have enough space for your seedlings to grow until they’re ready for transplant. You may find that you’ll need to bump up your seedlings into a larger tray so that they can continue to grow until it’s time to plant them outside.

50-Cell Seed Starting Tray

Speaking of more room, if there’s one flower variety I definitely recommend you give plenty of room to it’s sweet peas. Sweet peas are known for their large root system and for that reason I always use a 50 cell tray when starting my sweet pea seeds. 

In recent years, I’ve actually switched to using these 50 cell extra deep trays for my sweet peas as it allows for more root development.

We actually use these deep 50 cell trays for an increasing number of our crops- we start our ranunculus and anemone corms in these and I even pot up my paperwhites bulbs in these trays 

All of these varieties that I just mentioned are flowers that can benefit from a little extra space for their roots.

Now before you go crazy and grow all sorts of flowers in these extra deep trays- I will caution you, in my experience these trays are little more difficult when it comes to regulating moisture. Personally I feel like these trays don’t wick up moisture from their bottom drain holes as well and so I often find myself overhead watering when I’m using these trays verses bottom watering. And I just find it a little more difficult to actually gauge the amount of moisture at the very bottom of these deep cells. 

I think it’s much easier to maintain a consistent amount of moisture in any of these other more standard trays that are just 2 to 3 inches deep. 

20 Row Channel Tray

This next tray that I want to share with you is a little unique- it’s a 20 row channel tray. This is something I’d recommend if you are someone that hates sowing small seeds.

We all know the struggle that comes when you’re trying to sow something like snapdragons or herbs like oregano- the seeds are just so tiny it can be difficult to even decipher what’s a seed vs just a speck of dirt. I’ll admit, some seasons I have the patience to sit at my seed starting station I’ll use a moist toothpick to pick up each individual seed and put it into its own individual cell within my cell tray.

But other seasons, I find myself in a hurry or I just don’t want to bother with the especially tiny seeds. And in these instances, I will pull out my channel trays.

The purpose of this tray is that you’ll fill each channel with soil, you’ll indent your soil to create a small “channel” for seeds to be poured into. Unlike a cell tray where you’re placing one seed into each cell. With this tray you’re simply pouring seeds the length of your channel. Usually a single one-hundred seed packet is enough for one channel. As you can imagine this is a huge timesaver for getting seeds started.

Now I’ll treat my channel tray like any other seed tray- and I can fill more channels if I’d like- but I’ll usually put this on a heat mat and place a humidity dome over time. Once the seeds have germinated and my seedlings have put on just a little growth- I’ll pop these out of their channel and pot them up in my favorite 72-cell trays where they’ll continue to grow until I’ll plant them out in my garden.

For a lot of people, having to handle these baby seedlings is much easier than having to deal with the eye strain that can come from trying to separate tiny seeds into individual cells. 

A channel tray is a two-step process instead of just one like when you’re seeding directly into a cell tray- so you may have to do a little trial-and-error to see if this process works for you, but it is a great work around especially if you’re someone that struggles with planting small seeds. 

I’ll also use a channel tray if I have a flower variety that doesn’t have great germination. By planting lots of seeds in a single channel and then only bumping up the seeds that actually germinated I can avoid those instances where I have trays that have lots of empty spaces because the seeds I planted there simply didn’t germinate.

Seed Trays We’re Trialing this Year:

Now the last tray that I want to share with you today is a new tray that I’m trialing this season. And I’m honestly pretty excited about these.

So far in this post, I’ve shared with you the different types of trays that I use for my own seed starting practice. Realize however, that there is another method of seed starting that eliminates the need for any sort of tray at all.

This practice is what we call soil-blocking. Instead of planting your seeds into soil held in place by a tray, you plant your seed into a cube of soil.

There’s some great benefits to soil blocking- the biggest one being that it prevents your seedlings from becoming root bound. 

In a cell tray, when your seedling’s roots hit the side of the cell, they’re forced to grow downward in a spiral, and left in the tray too long they’ll often circle the bottom of the cell becoming root-bound as they tangle together.

Soil blocking, however, avoids this problem. When your seedling’s roots reach the outer edge of the soil block and actually come in contact with the outside air, they experience what we call “air-pruning”.  What this means is that root- it dries out and stops outward growth and signals secondary root development within the soil block. Overall you get a more developed, fuller root system for your seedling.

Despite these amazing benefits, I just don’t have the patience myself to plant my seeds into soil blocks- it can sometimes be a finicky process and I just much prefer the convenience of seed trays.

Air prune trays are sort of a hybrid method of seed starting that allows you to experience the benefits of soil blocking because the trays are designed in such a way that your seedlings can air prune themselves- but they have the added convenience of a tray.

I’ll be curious to see if my seedlings that grow in this tray are in fact healthier than those grown in my more standard trays. For this season, I’ve only purchased a handful of these air pruned trays so that I could get a feel for how they perform for me.

My plan is to use them on flower varieties that are particularly sensitive to root disturbance. My thoughts are that if I can grow a more robust root system on those sort of plants, they’ll likely transplant into my garden much more smoothly and overall perform better as they’ll have less chance of transplant shock – that’s at least my theory.

I will say that these trays are an investment. Still, they are incredibly well-made trays so I have no doubt that I’ll be able to use them for many seasons and in that sense, I’m not worrying about getting my money’s worth out of them.

But I’ll definitely keep you updated on how these perform for me as the season progresses.

Conclusion:

So there you have it- an inside peek into the different seed trays that I use in a season. I hope this blog post gives you some things to consider when you’re deciding on which trays you’d like to use in growing your own flower starts. 

Be sure to let me know in the comments below what you decide on as I’m always curious as to what other growers use!

P.S. Want to see all these trays mentioned in action?! Be sure to check out this YouTube video where I show you even more about my favorite seed starting trays!

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