This date, which is specific to your location, is the average date of the last spring frost as observed over several years. Contact your county extension service for the date.
A soil thermometer is the most accurate way to take your soil's temperature. Simply stick the probe into the soil and wait to see consistent readings for a few days. Plant when the soil reaches your crop's ideal temperature. A soil thermometer with an 8-inch probe costs about $9.
Dig down 4 to 6 inches, grab a handful of soil, and squeeze it into a ball. Then try to crumble it between your fingers. If it won't crumble and feels a bit like brownie batter, it's too wet. Wait a few days and try again. If it crumbles easily, it's ready for planting. If the soil slides through your fingers, it's too dry. Soak the soil and let it drain. Plant once it passes the squeeze test.
Figure out what soil temperatures your favorite vegetables prefer and what weather they can tolerate. Go here for the ideal temperature ranges of most vegetables. Use your last-frost date to establish planting dates. Just be sure that the soil is warm and dry enough before planting.
Regularly incorporating organic matter (compost, cover crops, etc.) into soil improves its tilth—physical condition and workability. A soil with good tilth drains well and is easy to cultivate, conducive to seed germination and root growth, and resistant to crusting. Learn more secrets to sowing success.