Using Open Flats (Seed Trays) to Grow Sturdy Seedlings Easily


We do use some plastic plug flats, pots, and trays of cell packs, but we also like to use our homemade wooden trays, because we can grow big sturdy plants in them, and reuse the flats year after year.

Make Your Own Seed Flats (Plant Starter Trays)

I recommend choosing a standard size for your flats, to make life simpler when fitting all the flats into your warm, sunny growing space, as well as when calculating how much to plant. We have a large garden, and we use flats that are 12 by 24 inches. We make two depths: 3-inch flats for sowing seeds, and 4-inch flats for growing the seedlings. I don't recommend flats bigger than that, as the filled flats get very heavy, and none of us needs to lift extra weight when that can be avoided by a bit of planning.

Lettuce seedlings.
Photo by Kathryn Simmons

We gather small scrap boards and make up a batch of flats at a time. We usually end up making a couple of half-sized 12-by-12-inch flats to use up the wood scraps. I like Eastern red cedar or pine. Avoid oak. Not only is it heavy, but it also splinters painfully, and it's not as easy to work with as soft woods. Avoid plywood and other manufactured boards, as the glues and fillers can be toxic to plants. Likewise, avoid pressure-treated wood.

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