By Polly Keary, Editor
It’s planting season!
Well, if you have a greenhouse, that is.
Right now is the perfect time to get a greenhouse up and start seedlings, said Kate Halstead, a Tualco Valley farmer who also coordinates agricultural workshops through the WSU Snohomish County Extension in Everett.
“This is the ideal time, “she said Friday. “I got seeds I started in mine yesterday. I put my peppers in.”
Never built a greenhouse before? It’s not as hard as it sounds. Halstead’s first greenhouse was a simple structure made out of plastic, cinderblocks and PVC pipe.
“I took two-foot lengths of rebar and pounded those into the ground in two rows, and then I took 20-foot pieces of PVC pipe and looped them over. Then I threw a sheet of construction plastic over it and weighted it with concrete blocks,” she said.
Now she uses lumber to build the bottoms of frames, but pipe is still an important structural item for the top.
If you aren’t that ambitious or handy, Lowe’s has a wide array of greenhouse products, from two-foot square structures for small plantings for about $40 to upright shelved structures that look like bakers’ racks in the $60 range. Tent-sized structures can be about $50, and low-to-the-ground cold frames run about $100. Moderately-priced 8’x12’x7’ structures run about $400, and at the top end of the scale are 25’x8’ peaked greenhouses for about $4,500.
Whether you build a greenhouse yourself or assemble one from a kit, one thing you are going to have to do is figure out how to control the temperature.
Greenhouses work because of the clear walls. When light passes through, it heats the air inside. The heat stays trapped, creating a warm environment well ahead of growing season in which seedlings can grow.
Even in the meager and weak sunlight of a Sky Valley February, the greenhouse can get warm enough to work in short sleeves most of the time.
But nights can get pretty cold, so Halstead has invested in a heat pad to put under her planters.
“I spend the money to get the nice mats that have the thermostat, and then you can kind of go cheap on the rest of the set up,” she said. “As long as the plants’ toes are toasty, the air can be pretty cold. I’ve had my seedlings survive freezing temperatures.”
The pads run about $50-$100, depending on the size. Smaller ones can hold about two flats, and larger ones as many as five. The thermostats also cost, too.
Ideally, a greenhouse will be about 70 degrees.
But a half-hour of direct sun, even on a cold day, can suddenly get the inside temperature a lot hotter than that.
“If the temperature gets to about 90, the plants start to stress,” she said. The thing to do is open the greenhouse door when the sun is out, but if you’re at work, you can’t do that.
“There’s ways to get around it,” said Halstead. “I’ve discovered if I keep their toes hot, I can open the door of the greenhouse before I go to work.”
Another option is a ventilation system with a fan and a thermostat that turns it on when the temps hit 85 degrees.
Once you have the structure in place and the temperature system worked out, then it’s time to start seedlings.
Halstead starts the plants that take the longest to produce fruit such as some peppers, or those she wants to be nice and big before she takes them outside and puts them in the ground.
Good starts for this time of year include cool season vegetables like broccoli, kale, cauliflower, bok choy and spinach. They can be transferred into the garden when days are in the 40s and nights above 32.
Once the seed sprouts begin to get their true leaves, the heat mats can be turned off, as the plants will then begin to prefer a cooler soil.
If your greenhouse is not getting enough light due to lots of dim and cloudy days, your seedlings may get leggy. The solution is to have some cool fluorescent bulbs over the flats. Put them on pulleys so they can be raised as they grow; keep them about two to four inches above the plants.
Tomatoes, peppers, eggplants and other warmer season crops can start in late March and early April. Those plants will also need heat and light to develop strong stalks. These don’t go in the garden until the temperatures hit the 60s, no matter how big and healthy they look.
Some plants can stay in the greenhouse all year; many people grow tomatoes entirely in greenhouses, and beans also do well when grown on stakes inside.
Plants that are going in the ground must be “hardened” before transplanting. About a week or 10 days before transplanting, start putting the plants outside during the day. The exposure to cold, wind and rain will acclimatize them to the outdoors, helping them avoid transplant shock.
Start out putting them in a shady spot; then after two or three days, start putting them somewhere they can get a few hours of morning sun. After about a week, the plants should be able to handle direct sunlight all day. Try to choose a cloudy day to plant.
A less labor-intensive method is to begin withholding water about two weeks before transplantation. Let the plants wilt slightly, then water them and let them wilt a bit again. After two weeks, the plants will be ready to transplant.