5 Best Summer Cover Crops to Refresh Tired Soil

9 July 2025, written by Barbara Pleasant

For most of us, the joy of harvesting potatoes, garlic and onions is followed by confusing questions about what to do next. You can still plant summer squash, cucumbers and dwarf beans if your first frost date comes after mid-October, but in most places it’s too hot to get moving with fall crops, which would rather wait for cooler weather.

This creates a great opportunity to refresh tired soil with a fast-growing summer cover crop. From buckwheat to sunflowers, the plants profiled here sprout and grow quickly in warm, moist soil. As they grow, they smother weeds, improve the soil with their extensive root systems, and help replenish soil nutrient reserves. Best of all, cover crop plants bring diversity to the soil’s microbial community, which can have lasting benefits to future crops.

Beans as a cover crop — Common beans attract an array of beneficial soil microbes when used as a summer cover crop

1. Convenient Beans

One of the good things about using beans as a summer cover crop is that you may already have seeds in your seed box. If not, buy a bag of dry beans at the market (red, black, navy, pinto, even a dry multi-bean soup mix), soak the seeds you want to plant overnight, and sow them thickly the next day. With good moisture and a shade cover to keep the surface from drying out, they should be up and growing within five days.

When grown as a tight stand, beans do a good job of shading out weeds. Below ground, beans don’t start fixing nitrogen until they are six weeks old, but meanwhile the roots are actively recruiting soil-borne rhizobia by feeding them nutrients via their root tips. If you pull out the beans after a month so you can plant a salad garden, the soil will be loose, friable, and teeming with microbial life, and you can compost the lush bean plants.

2. Benefits of Buckwheat

For smothering weeds, the best summer cover crop is fast-growing buckwheat. “For filling in between crops in the summer, it is hard to beat buckwheat as an easy and effective weed suppressor and soil mellower,” said Dr. Thomas Bjorkman in a comment to my article on The Benefits of Growing Buckwheat. Professor Emeritus at Cornell University in New York and an expert on buckwheat, Dr. Björkman also provided expert answers to many of the questions asked in the article’s comments thread. The result is a fantastic discussion about using buckwheat in the garden that you won’t want to miss!

Cowpeas aka crowder peas or southern peas — Crowder peas are a good summer cover crop in hot, humid climates

3. Crowder Peas for Warm Climates

Whether you call them crowder peas, southern peas or cowpeas, various selections of Vigna unguiculata have much to offer as a summer cover crop in hot summer climates. Growing best at temperatures between 75° and 95°F (25° to 35°C), this semi-tropical legume starts forming nitrogen nodules at an early age. You can use leftover seeds of culinary varieties for planting, or plant dry black-eyed peas from the store. Sow seeds thickly, only 2 inches (5 cm) apart, to get a good stand. The young plants are easy to take down when you need the space to plant something else. One good method is to use a mower or string trimmer to cut plants off at the surface, leaving the roots and their riches behind in the soil.

4. Speedy Sulphur Cosmos

Often called orange or yellow cosmos, sulphur cosmos (Cosmos sulphureus) is native to Southern Mexico where it is a familiar roadside weed. Like other “pioneer” weeds that colonise disturbed places, sulphur cosmos is armed for survival with rapid growth, vigorous roots that exude natural herbicides, and bright flowers that attract pollinators. When direct sown into any sunny space, sulphur cosmos will light up early autumn with colour, while providing sweet nectar for butterflies and pollen for bees.

5. Super Sunflowers

Last summer, a nearby organic farm grew sunflowers in a remote field where nobody would see them. It was my first introduction to growing sunflowers as a summer cover crop, for which they have many talents. As explained in this video from Michigan State University, robust sunflowers shade out weeds, provide forage for pollinators, and their vigorous taproots penetrate compacted subsoil. If you need seeds, the whole, unshelled sunflower seeds sold for feeding birds will do just fine.