Transitioning to the Fall and Winter Greenhouse

By Roger Marshall, "The Greenhouse Grower"

It’s hot. It’s humid. But mid-August is still the best time to start new seeds for transplanting into an unheated greenhouse to get a late fall and winter harvest. With any luck there will be chard, kale, cabbage, bok choy, pak choy, turnip, and snow peas ready to harvest for Thanksgiving and Christmas and thereafter throughout the winter. In another month I’ll also start lettuce, spinach, and other fast-growing greens for my winter greenhouse. By covering the crops with spun fleece, they will often last until mid to late March.

When starting seeds in seed flats in August to transplant into a fall greenhouse, you need to pick a cool, shaded area. I use a germination chamber in my cool basement. As soon as the seedlings have emerged, move them in their flats to a cool, shaded spot outdoors.

Right now the greenhouse is full of squash, melons, eggplants, peppers, cucumbers, and tomatoes. As the current crop of fruits and vegetables is harvested, these plants will be immediately removed to make way for new plants. I’ve found that it is false economy to keep a plant intact just because it has one more pepper or another cucumber on it that still needs to ripen. In a greenhouse where space is tight, it’s best to accept the fact that the summer harvest ends when fruiting slows down. Rip out the spent plants and start something else to keep your greenhouse production at a high level.

After removing the old summer plants, renew the soil with additives such as compost, blood meal, bone meal, or greensand, depending on the crop to be grown. As soon as the additives are watered in, plant a new seedling or two from your seed flat to fill in the open space. Of course, this means that from August though late September your greenhouse growing space will be a mish-mash of heat-loving plants that are being transitioned out and cooler weather plants that are being added. But it all seems to work out by early to mid October.

As the first snow falls, it is an easy walk from my kitchen to my unheated greenhouse to pick winter greens. Occasionally, I have to cut a path through the snow to get to the greenhouse, but it is worth it to know that the stew bubbling away indoors contains home-grown, organic vegetables that have travelled only fifty feet from soil to table.