In this area we usually start to plant our vegetable gardens about St. Patrick’s Day (March 17), sowing peas (shelling or mange tout) or potatoes first. Peas planted later in the season risk weevil invasions that render them inedible. Potato foliage may be damaged by late frost, but the resilient spuds send up other sprouts until they get some to last until blossom time or they think it should be blossom time (not all potatoes bloom).
Of course, you know Idaho is noted for its potatoes, even though our soil isn’t exactly right for them. The alkaline soil here can contribute to potato skin lesions called scab, but may be avoided by including some peat moss (acidic) in the planting hole or trench. Some potato farmers routinely add gypsum to their soil since it contains a small amount of sulfur, acidifying the soil. That’s also an attempt to make our soil less attractive to field bindweed (wild morning glory). Our soil in this area is commonly deficient in magnesium, and that may show up as chlorosis (yellowing of interveinal areas) or brown spots on leaves, but I haven’t had major problems growing potatoes other than quackgrass rhizomes growing through potatoes. Due to the proximity of quackgrass, two of my raised beds are not usable for root crops.
Some experts say the likelihood of seed potatoes’ rotting is less if you cut potatoes the day before planting, giving the cuts time to callus over, and the production may be increased if you chit the potatoes before planting. Chitting potatoes means putting them in a frost-free sunny area that’s about 50 degrees F., so that sturdy sprouts develop. Then when you cut potatoes for planting, allow at least one cubic inch of potato per eye. I prefer to plant seed potato pieces in a trench about 8 inches deep, setting potatoes 6 to 8 inches apart. Some folks set seed potatoes on top of the soil and mulch heavily over the top. Note potatoes for harvest will appear at the same level or higher in soil than the seed potato or potato piece.
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In early spring, many of us set out onion and other allium starts. Onions may be sets, seeds or seedlings, and for this area they should be “long day” or “day neutral” varieties. If they’re sets, narrow end up is the way to plant them. Onion sets may be covered by soil, but if you’re planting shallots, plant more shallowly, burying just up to the point where the clove begins to taper toward the head. My dog sometimes kicks the cloves out of the soil, but I just push them back down until they root. Deep-planted shallot cloves just rot if they’re planted too deep. Onion seedlings, even partly dried in a bunch, are sometimes tricky to plant. That can be made easier if you use scissors to trim the roots of each seedling to a fan shape, and also cut off the dead tip of the leafblade.
Be aware that onions are biennials, and that fluctuations in spring weather may convince your alliums that they’ve been in the ground for two years instead of two weeks or so. Onions and leeks that bolt to flower and seed are ruined for culinary use, but shallot flowers may just be pulled out without damaging the head.
Strawberries are also sensitive to the length of time they are exposed to sunlight. Locally owned nurseries sell long-day strawberry plants, but chain stores may sell the wrong varieties. When you plant, plant strawberry seedlings exactly as deep as they were grown, no deeper or no more shallow.
Early spring is the proper time to seed or transplant spinach, Swiss chard, most lettuces and other greens, since hot weather makes them bolt to flower-seed, leaving the leaves bitter. Lettuce, onions, parsnips and spinach seed can germinate if the soil is only 35 degrees F. Beets, carrots, Swiss chard, peas, radishes and turnips germinate at 40 degrees and warmer. Some brassicas (the genus that includes cabbage, broccoli, cauliflower) will germinate from seed when the soil temperature is 40 degrees, but when the soil is hot, such as in late July or August and you want to plant a crop for autumn, outdoor-sown seeds won’t germinate. Another garden vegetable that tolerates frosts (down to 28 degrees F.) is Florence fennel, the bulbing herb. Often when transplanting seedlings into garden soil I see volunteers that have already germinated at about 50 degrees F.
Of course frost tender crops such as corn, tomatoes, peppers, beans, cucumbers, melons, squash and eggplant should not be sowed until the soil temperature is 60 degrees F.
When starting seeds indoors, we usually try to heat the planting soil for all seeds, but not all seeds germinate in high temperatures. Seeds for many crops such as lettuce, parsnips and spinach won’t germinate if the temperature is too high. I have my heat mat set to 80 degrees for peppers and eggplant that I’m germinating now, but must wait until later to re-heat it for tomatoes, basil and tomatillos. They shouldn’t be started until close to transplant time. Setting them out in mid-May to June 1 usually works best.
Most brassicas or cole crops such as broccoli, cabbage, Brussels sprouts, collars, kale, and kohlrabi shrug off frosty weather, so they may be transplanted into the garden at this time. If we have a hard freeze forecast, a floating cover usually protect the plants. These are all easily germinated indoors at room temperature.
Send garden questions to email@example.com or Gardening, The Statesman, P.O. Box 40, Boise, ID 83707.