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Heat-Tolerant Cover Crops: A Summer Gardening Alternative 

Don’t let the heat stop you from gardening. Learn about heat-tolerant cover crops and how they can improve your soil health. 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. 

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

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

Healthy garden soil contains fungi, bacteria, protozoa, nematodes, earthworms, and more!

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.

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. 

The “soil food web” is missing a key component if nothing is growing.

After spring crops are harvested and temperatures rise, 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 soil’s life will suffer. 

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 or green manure instead. 
Cowpeas

At the very least, cover your soil with a thick 3-5 inch (7-12 cm) layer of mulch and water just 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. 

Ultimate guide to summer gardening in Arizona

Learn more about summer gardening in Arizona in this blog post.


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.

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

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. 
  • Cover crops attract and support native and beneficial insects and pollinators.
  • 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, a variety of heat-tolerant cover crops can provide these benefits. Let’s explore a few of the different types. 

Cowpeas are often grown as a cover crop in hot climates
Cowpeas are often grown as a cover crop in hot climates

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

Cowpeas are often grown as a cover crop in hot climates

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.

Cowpeas are often grown as a cover crop in hot climates

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. 

Take the summer off! Plant heat-tolerant cover crops instead 
Topping with compost can speed up the decomposition process

Learn more about how to grow cowpeas in this blog post. 


2. Buckwheat as a heat-tolerant cover crop

Buckwheat as a heat-tolerant cover crop

Buckwheat is a fast grower that goes from seed to bloom in about 30 days. It is often grown as a smother crop to suppress weeds. You can get seeds here. It is less heat-tolerant than some of the other cover crops. Plant buckwheat up until May for best results.

Buckwheat as a heat-tolerant cover crop

Good to know: Follow buckwheat plantings with transplants rather than seeds because buckwheat is allelopathic and may deter seed germination the following season.1

Buckwheat as a heat-tolerant cover crop

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.

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

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. 

Buckwheat as a heat-tolerant cover crop - Buckwheat 2 weeks after cutting back
Buckwheat, two weeks after cutting back

3. Sweet potatoes as a heat-tolerant cover crop

Sweet potatoes as a cover crop for hot climates
Planting sweet potato slips as a cover crop for hot climates

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). 

Sweet potatoes as a cover crop for hot climates
Sweet potato slips

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. 

Cut back the sweet potato leaves at soil level and then dig for tubers
Cut back the sweet potato leaves at soil level and then dig for tubers
How to Grow Sweet Potatoes #sweetpotatoes #gardening #garden #arizonagarden #gardeninginarizona #desertgarden

Learn more about how to grow sweet potatoes in this blog post. 



4. Tithonia as a cover crop in hot climates

Take the summer off! Plant heat-tolerant cover crops instead 
Cover crop of tithonia

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

Tithonia plants as a heat-tolerant cover crop

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.

Tithonia plants as a heat-tolerant cover crop

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. 

Please note: Tithonia is allelopathic and can inhibit the growth of some plants and seeds. Follow tithonia with transplants. However, studies demonstrate that due to increased soil fertility, using tithonia as a soil amendment may increase the growth rate of some plants.1


How to Grow Mexican Sunflowers: 5 Tips for Growing Tithonia

Learn more about how to grow tithonia in this blog post.


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 also be able to plant later. 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, so overwatering is unnecessary. Monitor the crops as they grow, and cut back at the appropriate time. 

Cowpeas sprouting for a heat-tolerant cover crop
Cowpeas sprouting

Perpetual Herb, Fruit & Vegetable Planting Calendar Zone 9b
  • 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

See the individual cover crops for the specifics about how and when to cut them back. In most cases, you will cut the cover crop off at the 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.

Cut off at soil level and top with compost if desired
Cut off at soil level and top with compost if desired

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.

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

You can also top with a layer of compost or incorporate the crop into the top few inches of soil. Topping with compost can speed up the decomposition process.

Tepary beans and cow peas as cover crops after cutting back
Tepary beans and cowpeas as cover crops after cutting back

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.

Cowpeas as a cover crop about two weeks after cutting back
Cowpeas as a cover crop about two weeks after cutting back

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Sources used in this article and further reading:

Chris

Monday 10th of June 2024

First thank you for all that you do in providing such useful advice for us gardening here in the valley. Would a cover crop be good for a flower bed where most of the plants are toast by mid-Jun/early July? And before I add a cover crop, do I chop & drop my dead flowering plants or cut and remove them? Thank you so much.

Angela Judd

Monday 10th of June 2024

Sure. You could plant a cover crop in a flower bed. I would probably remove the plants, not use them as chop and drop mulch.

Robert

Friday 19th of April 2024

What about tepary beans?