Packets for some vegetable seeds say "plant as soon as the soil can be worked."
I don't find that very useful information, and if you don't either, I think these are better instructions.
After snow has melted and spring rains have ceased temporarily, look at your garden soil. If water puddles around your foot, it's too wet. If a bed is wet and soggy, don't walk in it, for that will compact the soil. If you feel you must get into the garden, lay boards to spread the effect of your weight, and walk only on them.
You won't need to start planting anything though until the soil temperature has warmed to at least 40 degrees F. If your garden is in raised beds, remember they'll warm up earlier than ground level soil. Pick up a handful of soil and squeeze it. If it fails to "ball" then it's quite dry. If it does "ball" poke it with a finger. If it just indents, it's still too wet. If it falls apart, it's good.
If you played marbles outdoors, you may remember the time to play marbles was when the crust of the earth had a crepe-like surface, tiny ridges dryer than the valleys. That spells gardening time to some of us.
Many of us plant potatoes first, but should we? You should wait until the soil has warmed to 50 degrees to plant potatoes. I think I've planted potatoes in soil colder than 50 degrees, but that did delay their growth. Potato leaves may be blackened by frost, but they'll recover.
Other crops would thrive in cooler soil. Most lettuce varieties love cool weather, and lettuce seeds will even germinate in soil as cold as 40 degrees F. If you've started lettuce indoors, transplants will withstand light frosts. I'd set out seedlings at 40 degrees soil temperature, but I could lose them to frost. Older seedlings tolerate frost better than young ones.
Even though soil is still cool at 40 degrees, peas will germinate at that temperature too. They often are slower to germinate than I'd like, though, so I sometimes sprout them indoors and then plant the sprouts. To sprout, put them in a quart canning jar, topped with a square of nylon net affixed with the jar ring. Leave that in place while you sluice the peas a few times each day with lukewarm water, each time draining the water and laying the jar on its side out of direct sunlight. In about three days, the peas should be well sprouted, so plant those outdoors. The sprouts are really roots, but they'll find their own way down if laid on their sides.
Chinese cabbage, pac choi and mustard greens also germinate when the soil temperature is about 40 degrees. Their optimum germination temperatures run from 40 to 75 degrees. Hotter soil kills these seeds and those of Brassicas and other frost-tolerant vegetables if you try to direct seed in warm to hot soils in midsummer.
You can direct sow beets when the temperature is 45 degrees F. Incidentally, it's a good idea to cover beet plantings until the seedlings are well-established, because those tiny leaves look like a banquet to birds.
Onions, collards, cabbage, kale and other Brassicas prefer slightly warmer soil, about 55 degrees minimum. Celery, too, will germinate at 55 to 75 degrees.
I've never planted celery out before the average last date of frost, so I'm not sure how it would handle frost. I did have some celery overwinter two or three years ago, surviving hard frosts, but celery we harvested one fall and unintentionally left the box outdoors was left limp by frost.
A light frost will nip but not kill corn seedlings, but some folks in this valley wait for the soil to warm to 60 degrees before planting seed corn. The late Ross Hadfield waited until June before planting his corn. If you do that, note the days to maturity on the seed packet. August ripening seems to be the best time for sweet corn harvest.
If you intend to sow flower or herb seed, check the seed packet for best temperatures for germination. In general, flowers should not be sown before soil warms to at least 55 degrees, herbs at least 60 degrees F.
Send garden questions to firstname.lastname@example.org or Gardening, The Statesman, P.O. Box 40, Boise, ID 83707.