Mini-Hoop Keeps Seedlings Warm

Reader Contribution by Ilene White Freedman
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Spring is full of babies and birth, and the greenhouse is no exception. Plant the seeds and nurture them… wait for it… and the baby plants emerge from the soil and stretch toward the sun. It’s called a nursery for a reason. I visit the trays of baby plants and feel their energy, budding with all the hope and promise of a new season. I showed a seed tray to a young intern. The tray was right on the verge of germinating, with only the first glimpse of a couple seedlings popping up. Brand new freshly emerging baby cabbage plants. She caught my drift and said “awwww!” just like she was looking at the cutest newborn baby and in on something special. That’s the reaction I was looking for, that amazement at witnessing new life. Could have been a baby human, puppy, any animal or plant, they all start out cute, miraculous, and vital.

A little biology lesson here. The seedling first germinates with the cotyledon, its embryonic leaf. My photo (left) shows the cotyledon of the cabbage seedling. Cotyledon leaves are simple in form. Isn’t it cute?

The next leaf to sprout is called the true leaf (photo right). It’s a miniature leaf too, but it looks like a cabbage leaf in all its detail.

Pepper, eggplant, and tomato cotyledons all have a simple v-shape cotyledon and then their true leaf distinguishes them from each other.

How do we keep these babies warm in March? We’ve created a mini-tunnel inside our high tunnel. We grow our seedlings on a long table along the 100 foot long side of our high tunnel. The high tunnel is not heated. We have electric heat mats on the table to directly heat the soil in the trays, not the air in the whole hoop. For extra warmth at night or on cold days, we keep a plastic tunnel over the table. It is great at holding in the heat from the tables. We drilled a hole every few feet in the tables and popped hoops over the table. Then we have greenhouse plastic draped over the hoops. It keeps the warmth and moisture in. We pull it back with clips during the day. You might notice the white perlite in the seedling trays. Our trays are in a warm moist climate. We do get a little touch of green algae on the surface of some trays, so we cover the seeds with a thin layer of perlite. Seeds pop out of it easily, and it protects the soil surface, preventing damping-off mold on tomato seedlings.  

Photo 1: Cabbage seedling in its cotyledon form. 
Photo 2: Cabbage seedling with its cotyledon leaf and its first true leaf.
Photo 3: Seedling tables set up with hoops and greenhouse plastic for a mini-hoop in the hoophouse.

Ilene White Freedman operates House in the Woods organic CSA farm with her husband in Frederick, Maryland. She blogs about making things from scratch, putting up the harvest, gardening and farm life at, easy to follow from our Facebook Page.For more about the farm, go to