Offer Protection On Chilly Nights
Nurseries are full of tempting tomato plants right now, including fabulous varieties that are all but irresistible. It’s wise to buy these beauties when you find them, as pickings can get thin as the season progresses. However, gardeners should be aware that in many areas, tomatoes will need some help to make it through the night. Really? Well, yes. Though the days are getting warmer and the sun has reappeared, our Northwestern nights continue to be on the chilly side. Tomatoes don’t thrive in cold air or cold soil, so offering some protection will ensure a far better crop.
Until night temperatures remain above 55 degrees F, tomatoes need help to stay in shape. Those lower temperatures don’t just check growth, they can actually set back tropical heat lovers like tomatoes, peppers, eggplants, corn and squash. While peas enjoy cooler weather, their bean cousins don’t, and beans, too, fare better when temperatures remain above the mid-fifties at night. Research has demonstrated that 55 degrees is the critical temperature point, and that when air or soil temps dip below that mark, tropical plants will drop blossoms and roots may actually shrink a bit.
Highs And Lows
Back in the day, we used soil thermometers which have little markers that register the day’s high and low temperatures to determine when it was safe to plant tender crops. These days, most Smartphones show hourly temperatures for each day; when night temps have remained over 55 for a week, plants can go in the ground, but given the wobbly Northwestern weather, protection is still a good idea. While you’re waiting, keep plants indoors under grow lights or at least bring them in to a warmer, protected environment at night.
When soil warmth arrives, plant tomatoes in trenches, placing 3-6 inches of main stem under the soil and filling in the trenches as you plant. This deep planting would kill some things, but tomatoes grow fresh roots from that buried “neck.” Deep planting helps the fully loaded plants remain upright, especially indeterminate tomato plants, which get huge unless pruned. However, if you’re planting the super-productive grafted tomatoes, it’s important NOT to do this, since if the grafts are buried, the plants will lose the benefits of vigor and disease resistance offered by the rootstock. Plants grafted tomatoes and other grafted vegetables so the roots are at the same depth as they were in their pots and you’ll be rewarded with amazingly abundant crops.
Better In Every Way
In cooler areas like my island home, grafted tomatoes offer extra resistance to the challenges of wayward weather. Even so, in cold or coastal gardens, it’s important to keep tomatoes warm, and not just because we want great production Studies show that produce from less stressed plants will look and taste better and be nutritionally superior to crops from plants that are struggling to survive. Happily, a few easy techniques will promote plant development and improve fruit size, flavor, and nutritional quality.
Unless you can give your tomatoes full sun (10-14 hours a day), they may do better in a large pot than in the ground. Ideally, each plant gets a pot that holds 2-3 cubic foot-sized bags of potting soil. Since I’m limited to a corner of someone else’s garden this year, my tomatoes are growing in large black plastic tree pots scavenged from friends. One benefit is that soil in these will warm up faster than the ground, and they also hold heat quite well. If you’re gardening on a deck or other hard surface, keep large pots manageable by setting them in large, wheeled saucers BEFORE you load them up with soil. This way, you can wheel them around to follow the sun. When I gardened on my own deck, I rolled my tomatoes under cover at night in cold or rainy weather, and the plants definitely benefited. Here I can’t move them, but I can always toss a sheet of woven row cover over them if need be.
For plants in the ground, red plastic sheet mulch both insulates soil and may boost production by as much as 30%. In one study, researchers mulched one large group of tomatoes with black plastic, another bunch with clear plastic, and a third section with red plastic sheeting. If your garden is windy, young tomato plants will benefit from water-filled protective covering (Wall-O-Water is a common kind). I’ve also wrapped the sides of tomato cages with two layers of bubble wrap, with an attached top flap that can be flipped off in the day and flipped on at night. leaving the tops open. By the time the plants size up, it’s warm enough to remove the protective jackets and by then, the plants need better air circulation as well.
Indeed, tomatoes often suffer foliage diseases when they remain damp overnight. My favorite tomato cages are in use at the Harmony Hill Retreat Center, where cool breezes off Hood Canal can stunt tomatoes and peppers in cool summers. To prevent this, the clever gardeners construct greenhouse-like structures over each bed. Neither expensive nor fancy, these sturdy, moveable frames have straight sides about 4 feet high, topped with an A-frame roof that peaks 6-7 feet above the ground. That’s large enough to accommodate big, indeterminate tomatoes without crowding (which also leads to disease problems). In early spring, they wrap the sides, top, and ends in heavy translucent plastic sheeting. As the days warm up, the sides and ends come off, leaving the top covering in place. The result is generous crops of fat, red tomatoes with tiptop flavor.