Planting Vegetables in Midsummer for Fall Harvest

After harvesting early-maturing vegetables such as salad greens, radishes, peas and spinach, gardeners can plant other crops in midsummer for fall harvest. Some root crops, greens and other vegetables can be successfully grown from late June, July or even August plantings. It’s important to know the average first frost date in your area, in order to calculate when to plant these late vegetables so they’ll mature before being killed by cold weather. Find the average first fall frost dates in your area using Minnesota’s Climate Divisions map along with the following descriptions.

Some vegetables will tolerate a fair amount of frost and keep growing even when temperatures are in the low forties. Others can’t tolerate frost and stop growing in cool weather. Bush snap beans, for instance, mature in 45-65 days, but even a light frost (temperatures between 30º and 32ºF) will kill the plants. Kale, on the other hand, takes just as long to mature, but plants continue to grow when temperatures are cool, and can survive cold down to about 20ºF. So cool-season vegetables including kale and others in the cabbage family may be the best choice for mid-summer sowing, because an earlier-than-expected frost won’t kill them before they’re ready to eat. Many of the cold-tolerant vegetables actually have better quality when grown in cool weather; it’s said that the frost “sweetens” them. The following table provides information about recommended late-season vegetables.

Vegetables for mid-summer planting

Leafy vegetables, such as Swiss chard, kale and mustard greens can be harvested before the leaves reach full size. Often these small leaves are more tender and tasty than mature ones. These crops can be planted in succession every few weeks over the course of the spring and summer, to provide a steady supply of young leaves. Lettuce tends to bolt and taste bitter when grown in the heat of summer, so just enjoy it in spring or wait until temperatures cool to plant a late crop. Shade from taller plants may help improve the quality of summer-grown lettuce, as will selecting varieties suited for warm weather.

Basil and cilantro are fast-growing herbs that are ready for harvest about a month after sowing the seed. Garlic planted in September produces the biggest bulbs the following July, so after harvesting a late-maturing crop, you can plant garlic in that space.

Before sowing these second crops, turn over the soil and mix in some balanced fertilizer to replace what earlier plants have used up. Left-over debris like stems or roots from the first planting can cause problems in seed germination if they aren’t removed or allowed to break down, so wait a week or two before seeding the second crop, or be sure to remove this material as completely as possible.

Green Manures

If it’s too late to plant a second crop of vegetables, you may want to plant “green manure” to keep the area weed-free, prevent soil erosion, and add organic matter to the soil. Green manures include legumes such as vetch, alfalfa, clover, and peas; grasses such as annual ryegrass, oats, winter rye, and winter wheat; and broadleaf plants such as rapeseed and buckwheat. Sow seed thickly to create a cover that won’t allow weeds to compete. Mow these crops down if they flower before they’re killed by frost, to prevent them from self-seeding and becoming weeds.

In late fall or early spring, turn dead plant material from green manures into the soil before sowing seed or planting seedlings. This is also the time to add fertilizer to the soil. If the green manure is one that doesn’t die over winter, wait about two weeks after you turn in the living plant material before seeding or transplanting your crops. For more information on green manure, see current fact sheet, (add hyperlink when this fact sheet is available).

Reviewed by Cindy Tong, Extension Post-Harvest Horticulturist, University of Minnesota Extension, 1-08 and Vince Fritz, Extension Horticulturist – Vegetables, University of Minnesota Extension 1-08.