When to Plant Bean Seeds: Frost and Soil Rules

Step 1: Find your last frost date

Beans cannot take a freeze. A Clemson Cooperative Extension factsheet says bean seeds do not germinate well in cold soil and light frost kills the plants. A University of Illinois Extension page says to plant after all danger of frost has passed in spring.

So start with the average last frost date for your area. Your county extension office or a weather-station table will give it. The date is an average, so it can still frost after it.

Beans reward patience, and a seed in cold wet soil loses to a seed planted a week late.

Step 2: Know when to plant bean seeds by soil warmth

Frost date gets you close, and the soil settles it. Clemson says not to plant beans before the soil is at least 60 F at the 4-inch depth. Push a soil thermometer in 4 inches and read it.

If the soil has warmed early, Illinois allows an early sowing a week to 10 days before your average last frost date. Say your last frost date is May 10. That early window runs from April 30 to May 3, and only when the thermometer already shows 60 F.

Warmer is better. A K-State Research and Extension guide lists 70 to 85 F as the optimum temperature for bush beans, and 5 to 8 days to germinate.

Step 3: Sow one inch deep, one seed at a time

Both extension pages say to plant bean seeds of all varieties one inch deep. For bush beans, Illinois says to set seeds 2 to 4 inches apart in rows at least 18 to 24 inches apart. That means one seed per spot, not a handful in a hole.

Pole beans differ. Illinois gives two ways. Plant seeds 4 to 6 inches apart in the row, or in hills with four to six seeds per hill, set 30 inches apart.

Keep pole beans out of the corn rows. Illinois answers a question about planting pole beans at the base of corn with a plain no, because neither crop reaches its full yield.

Step 4: Skip the soak and water after

Do not soak bean seeds. Illinois says seeds of most varieties tend to crack and germinate poorly when the soil's moisture content is too high, so it advises never soaking them. Water just after planting, or plant right before a heavy rain.

Clemson adds one more tip for cool soil. Treated seed helps prevent seed rot when seeds go in early. Check the packet to see whether yours is treated.

Indoors or in the ground

Sow beans where they will grow. A Clemson factsheet on starting seeds indoors says beans, corn and carrots do not do well as transplants and should be planted directly from seed into the garden. Skip the tray, and spend the effort on the soil check in Step 2.

Why bean seeds rot or never come up

Four causes show up in the sources. Each has a fix.

• Cold soil. Bean seeds do not germinate well in it, per Clemson. Wait for 60 F at 4 inches.
• Soil that is too wet. Illinois says seeds tend to crack and germinate poorly when the moisture content is too high. Never soak the seed, and water after planting.
• Seed rot in early sowings. Treated seed helps prevent it.
• A late frost. Light frost kills the plants (Clemson), so an early sowing near your last frost date carries that risk.

Step 5: Count back from fall frost for a late sowing

Beans can go in twice. Clemson suggests planting every 10 to 14 days for a continuous supply, and Illinois says you can keep sowing until early August.

Use a countback to find your own cutoff. Snap beans are ready about 55 days after planting, says Clemson, and the Georgia chart gives bush beans 50 to 60 days. Take your average first fall frost date and subtract 60 days. If frost usually arrives October 20, the last bush bean sowing falls on August 21.

Doing this for beans is easy. Doing it for tomatoes, peppers and squash in the same week is where it gets tedious. The Winter Plan has a fall countback worksheet with a worked example that does the subtraction for each crop.

What your own month looks like

State extension offices publish a sowing window for beans instead of one month. The table shows three of them, so you can see how far the answer moves.

Georgia's spring window is 47 days long, from March 15 to May 1. Your window starts with your own last frost and the 60 F reading, so use these as examples and not as your dates.

When a free state chart is the better pick

If your state extension already prints sowing dates for your county, use them and skip anything else. Free charts and printables are enough for a single bean row, where a thermometer and the table above do the job.

A printed kit helps when you want sowing weeks counted from your own last frost for every crop. It is not tied to one zone, because a table of last and first freeze dates (10, 50 and 90 %) for 108 NOAA stations sits in the file. For beans, the seed order calculator and the paper towel germination test (7 days) come in winter, the spring week list holds the sowing week, the succession waves page holds each 10 to 14 day resow, and the notes for next winter page records what to change.