Take the summer off. Plant heat-tolerant cover crops instead!

Too hot to garden? Take the summer off and plant a heat-tolerant cover crop instead. Planting a cover crop after spring crops finish is an excellent way to improve your soil while waiting for the more bearable temperatures and fall planting season. Learn which cover crops grow well in hot climates, when to plant them, and what to do at the end of the season with the tips in this blog post. 

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Beat the Heat: Revolutionize Your Summer Garden with Heat-Tolerant Cover Crops

Is it better to not plant anything during the summer? No! 

Garden soil is full of life we can’t see – fungi, bacteria, protozoa, nematodes, earthworms, and more! Fungi and bacteria feed on the nutrients in the soil emitted by the plant’s roots. The soil food web is missing a key component if nothing is growing. 

After spring crops are harvested, and temperatures are rising, it may be tempting to leave the ground bare and return when temperatures decline in the fall. However, doing this can have a detrimental effect on your soil. Bare soil will dry out, heat up, and become compacted, and the life in the soil will suffer. 

At the very least, cover your soil with a thick 3-5 inch (7-12 cm) layer of mulch and water enough to keep the soil from drying out over the summer. 

If you don’t want to garden and want a mostly “hands-off garden” during the hottest months of the year, plant a cover crop instead. 

Why plant cover crops in hot climate areas? 

Cover crops are great for capturing and recycling nutrients in your soil. Leguminous cover crops like cowpeas can even fix nitrogen from the atmosphere, enriching your soil.

Some of the benefits of growing cover crops include: 

• Cover crops can lower soil temperatures by keeping the soil surface shaded. 
• There is less water lost through evaporation from the soil’s surface. 
• Cover crops add organic matter to the soil and feed the microorganisms. 
• Over time, cover crops can improve soil fertility, structure, and moisture capacity. 
• Summer rainfall will soak into the soil with plants and established root systems rather than running off or eroding the soil. 
• Cover crops often suppress weeds.

Which cover crops grow well in hot, dry summers? 

Luckily, there are a variety of heat-tolerant cover crops that can provide these benefits. Let’s cover a few of the different types. 

1. Cowpeas (black-eyed peas) as a cover crop in hot climate areas

Black-eyed peas are legumes that can withstand high temperatures and enrich the soil through nitrogen fixation. Their deep roots absorb and retain water for growth and are a nutritious food source. Taller vining varieties produce vigorously and are well-suited for cover crops.

How to plant: Direct seed into the garden. Plant seeds 1 inch deep and 4-6 inches (2.54 cm deep and 10-15 cm) apart. I plant 8-10 per square foot gardening. Get seeds here.

Time required: About 75 days before cutting back. Plant in bed 2-3 weeks after cutting back.

When and how to cut back: When they begin to bloom, cut off at soil level or pull from soil to prevent regrowth. Leave plants on top of the soil or cover with compost. 

2. Buckwheat as a heat-tolerant cover crop

A fast grower that goes from seed to bloom in about 30 days, buckwheat is often grown as a smother crop to suppress weeds. Get seeds here.

Good to know: Follow buckwheat plantings with transplants rather than seeds because buckwheat is allopathic and may deter seed germination the following season.

How to plant: Scatter seeds about 4 inches (10 cm) apart. Seeds sprout quickly. 

Time required: 30-40 days before cutting back. Plant in bed 1-2 weeks after cutting back.

When and how to cut back: Cut back buckwheat during blooming to prevent seed formation and dropping. Cut off at soil level. Leave plants on top of the soil or cover with compost. 

3. Sweet potatoes as a heat-tolerant cover crop

With a long growing season, deep roots, and sprawling vines, sweet potatoes are an easy-to-grow cover crop option that produces edible leaves and tubers (depending on when you harvest them). 

How to plant: Plant sweet potatoes from slips (learn how to make sweet potato slips in this post), spaced 12-18 inches (30-46 cm) apart.

Time required: 90-120 days before cutting back (you can cut back sooner if you don’t want edible tubers). Plant in bed 3-4 weeks after cutting back.

When to cut back: Cut back leaves 2-3 weeks before your desired planting date. After cutting off leaves, dig at the base of the plant and remove any developed tubers (sweet potatoes!), then pile leaves on the soil. Leave plants on top of the soil or cover with compost. 

4. Tithonia as a cover crop in hot climates

Tithonia is a large plant that produces a significant amount of plant matter. This vegetation decomposes quickly and may improve soil fertility when used as a chop-and-drop mulch. 

How to plant: Allow 2 feet (0.61 m) between plants. Seeds can take 10-15 days to germinate. Consider starting seeds indoors 6-8 weeks before your desired planting date. Tithonia seeds need light to germinate; cover lightly (¼ inch / .6 cm) with soil.   Click here for seeds.

Time required: 60-90 days before cutting back. Plant in bed 2-3 weeks after cutting back.

When and how to cut back: Cut back before stems become woody and the flowers produce seeds. (Remove seed heads if necessary.) Chop up plant matter and leave it on top of the soil. 

When is the best time to plant heat-tolerant cover crops in hot summer areas? 

Begin planting cover crops after spring, and early-summer vegetables finish from about May through June or early July.

You may be able to plant later as well. Count back from your desired fall planting date to see if there is enough time for the crop to germinate, grow, and die back.

Monitor seed-grown crops and keep the soil moist until the crop germinates. Once crops germinate, give cover crops water as needed throughout the growing season.

These heat-tolerant cover crops are somewhat drought-tolerant; overwatering is unnecessary. Monitor the crops as they grow, being sure to cut back at the appropriate time. 

• PLANTING GUIDE: Each month lists vegetables, fruit & herbs to plant outside & seeds to start indoors.
• HARVEST GUIDE: Photos show what may be ready to harvest that month.
• Planting dates are for the low desert of Arizona (zone 9b).

What to do after cutting back cover crops

In most cases, cut the cover crop off at soil level and leave the crop on the surface as mulch. Leave the roots in the ground, as they’ll continue to add organic matter and nutrients to your soil.

The plant matter from your cover crops is an excellent source of organic matter and nutrients for your soil. Instead of removing the cuttings, leave them on the surface of your raised beds. Over time, they will decompose and improve soil structure, water retention, and fertility.

You can also top with a layer of compost or incorporate the crop into the top few inches of soil. 

Generally, wait at least two weeks before planting the next crop. To plant, move the residue aside and plant your seeds or seedlings. Then, move the residue back around the plant to serve as mulch.

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