How to Choose the Right Size Pot for Seed Starting

Choosing the right pot for your seeds isn’t something to overlook. A pot too small will lead to rootbound seedlings quickly. A too large home for small seeds may run the risk of waterlogging them rather easily, which will stunt their growth.

Our OG seed starting trays: this is half of a 72-plug tray, that probably came with a self-watering reservoir too. There’s a link to a system like this on my amazon storefront (affiliate link).

The goldilocks rule for me is as follows. Sow seeds into a minimum 72 plug tray or 2” soil block. Of course, you’ll read and about exceptions below, but for veg, this is where the majority of them start.

This might be the end of the container needs for many seedlings, as transplanting into the garden is not too far off. If you can time it, that’s ideal: less inputs and resources needed before they are outside in your ground and enjoying sunlight. For my needs, this includes things like cabbages, head lettuce, broccoli, kale, brussels sprouts, bok choy, and summer celery. If plants only need about a month head start, they can safely stay in that first soil block or pot as you harden them off and prepare for transplanting.

But for slower establishing plants such as tomatoes, peppers, eggplants, and spring celery, you’ll need to bump them up (up pot them, or pot them up … interchangeable phrases for transplanting into a larger pot) at least once before the ground is warm and welcoming enough to accept them.

The seed starting tray, above, a 128-plug tray. I don’t recommend you use even though I still will, for a small group of flowers, because the trays are still functional.

Then there are flowers. I admittedly don’t give the same root space needs to my flowers as I do to my vegetables. I tend to crowd them, because I am often short on grow lights at this time of the season and I’ve found that even though it’s fraught with challenges, the large trays allow me to seed hundreds of flower starts in a small amount of space.

Here’s my list of what size pot I use for different seeds:

 4” Plastic Pots

• Onions
• Leeks
• Shallots

2” Soil Blocker, or the equivalent: 1.5” cell / 72 plug tray

• Tomatoes
• Peppers
• Eggplants
• Celery
• Brassicas
• Beets
• Head lettuce
• Bok choy
• Cape Gooseberry
• Tomatillo
• Ground Cherry
• All herbs, including fennel
• Nasturtium
• Calendula
• Globe amaranth
• Strawflower
• Dahlia
• Tithonia

3.25” Newspaper Pots

• Peanuts (2 seeds per pot, split at transplanting)
• Squash
• Zucchini
• Cucumbers
• Melons
• Sunflowers

Melons and sunflowers both don’t enjoy being transplanted so I circumvent that with newspaper pots that are easy to rip open at transplanting time, keeping the roots from protesting from being torn out of a plastic tray or pot.

 1” plug tray (128 cell) (the one I don’t recommend using, but because I know you might anyway …)

Annual flowers only:

• Zinnia
• Cosmos
• Marigold
• Sweet alyssum