The Iowa Gardener

The coolness or warmth of the soil (rather than the air) is key in knowing when to plant seeds or seedlings outside directly in the soil.

There’s an old saying that Iowa farmers know that the soil has warmed up enough to plant corn when they drop their drawers and can sit on the ground comfortably. But it’s a bit more practical (not to mention modest) to be scientific about it. A soil thermometer can be a cold-climate gardener’s best friend.

Most seeds—especially early in the season—are picky about the temperature of their soil. Here in the Midwest, the weather can vary so wildly that ideal planting times can also vary by up to three or so weeks. So don’t leave it up to chance: Invest in a soil thermometer to tell you the actual soil temperature in ajust a minute or two. They start at about $10 and are easily findable online by searching for “soil thermometer”.

Listed below are the soil temperatures at which various vegetables should be planted.* The plants with an asterisk next to them are usually planted as small plants or seedlings rather than planting the seeds directly in the soil. The temperatures are based on temperatures taken at 8 a.m. at 4 inches deep. (For beans, take the temperature at 6 inches.)

Cool-Season Crops

Warm-Season Crops

Source: Colorado State University Horticulture Extension
• Usually planted as established seedlings, not as seed.

Other Links of Interest:

How To Direct Sow Seeds In Iowa

The Easiest Plants To Start From Seeds

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