Margaret Lauterbach

It’s that time again: Know your greenhouse and soil rules

Just as soon as the post-holiday sales have concluded, general stores will start stocking and selling garden items. Gardening is a major focus of goods for sale from early January until Labor Day. Some of you, dreading the loss of your aphid “friends” for the duration of winter, have invested in greenhouses. There you can continue your relationship if your greenhouse is sufficiently warm and there’s a millimeter-sized crack through which one aphid could squeeze. That’s all it takes. Aphids reproduce parthenogenetically, just the single aphid, pumping out babies, and they, in turn, can produce them almost immediately.

There is more to greenhouses than aphids, however. Some folks intend to grow vegetables over winter, and that’s doable with some reservations. Many people advise home gardeners against trying to grow tomatoes indoors over winter. Too many growers assume that the tomatoes that grew well outdoors will do well inside, too. They don’t, but there are special varieties bred for greenhouse growing that are bred to have “short internodes,” so are more compact than outdoor varieties. “Short internodes” means stems are short between leaf joints.

Some commercial growers tie tomato plant tops with cord and tie that to overhead fixtures to keep plants upright instead of caging them. A big problem with growing tomatoes in greenhouses is moving pollen from the male parts to the female parts. You won’t obtain fruit unless this is accomplished. Tomato flowers are whole and perfect, containing both male and female parts in each blossom, so they’re self-pollenizing – outdoors. Indoors they don’t have insects or wind to move the blossoms.

Some beekeepers maintain that it’s the “sonication” that really pollenizes tomato blossoms. Sonication is the sound vibration of a bee. Heeding that, some growers use electric toothbrushes to sonicate their greenhouse tomato plants. I haven’t seen this in operation, so I don’t know whether sonicating each flower is necessary, or just treating each plant.

A major problem in growing food in greenhouses over winter is the shortened hours of sunlight. Most plants thrive when there’s at least 10 hours of sunlight each day. We lost that length of sunshine about Nov. 6, and we won’t get it back until about Feb. 6. Thus if you want to grow food over the winter, you’ll need to supplement sunlight with electric light, such as a plant grow light or fluorescent light positioned close. Grover’s Pay and Pack people are knowledgeable about that, and can be of great help.

I use my lean-to greenhouse mainly for overwintering special chile plants and a kaffir lime tree, and in late December to early spring, to house newly sown seedlings. Days are getting longer, so spring is on the horizon. I know the calendar says winter has just begun, but I smell spring. The aroma is sufficiently strong to prompt me to start sowing seeds. Onions, shallots and leeks are already poking up through planting mix, but they won’t be transplanted for a few months. My new seedlings will be “hardened off “ (acclimated) and then transplanted into the garden when each plant’s tolerance has been reached.

Frost-tolerant brassicas will be set out first, once the soil temperature is about 60 degrees. Since I grow in raised beds, soil temperature will warm before ground soil temperatures rise. Soil thermometers are not hugely expensive, so I would strongly advocate your obtaining one. Below 40 degrees, for instance, many transplants and seeds will just die, and plants struggle in 50-degree soil.

I went through some of my old files during my hiatus, and I’m now convinced that soil temperature is vitally important when transplanting. I plan to transplant only after soil has warmed to 60

I hope this is more binding with myself than New Year’s resolutions. I know I’ll be sorely tempted to plant out onions, leeks and shallots earlier, but that’s the kind of mistake that can lead the onions and leeks bolting to flower in the belief they’ve gone through a cold winter. When onions and leeks go to flower, the stalk arises from inside the bulb area, destroying their usefulness. When shallots go to flower, the stalk arises next to the edible bulbs, so can be easily pulled out without damaging the bulbs.

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