Summer Gardens – Dealing with High Temps in the Garden

Most summer gardens are in full swing by early July; the plants are growing like crazy and the harvest is finally coming in. The days are wonderful…. and hot.

While summer vegetable crops do love heat, there is only so much they can take. Understanding how heat affects you and your crops will make gardening in the heat more productive.

What are Heat Zones, and How do they Affect Your Summer Gardens?

Most gardeners are very familiar with cold hardiness gardening zones; however, not many are familiar with heat zones. Heat zones were established by the American Horticultural Society to easily describe how many heat days an area has. A heat day is defined as any day the high temperature reaches 86°F or higher.

There are 13 heat zones in the United States and these do not correspond with the cold hardiness zones. So you may be in a cold hardiness zone 9 but a heat zone 5. Don’t confuse the two. (Heat-Zone Gardening: How to Choose Plants That Thrive in Your Region’s Warmest Weather is an inexpensive guide focused on heat zone gardening.)

Knowing your heat zone and the average number of days you can expect to have temperatures over 86°F will help you decide how to manage heat in your summer garden.

If you live in a heat zone 5 and you only have about 30 heat days a year, you will deal with that differently than someone who lives in a heat zone 9 and gets 150 heat days a year.

What heat zone are you in and how many heat days can you expect? Check out the AHS Plant Heat Zone Map here.

If you live outside the US, you can look at archives from your weather service and count the number of days your area has degrees over 86°F.

Working with Your Growing Season

First thing to consider – how quickly in the season does your heat come on? If you have really cold winters and hot summers, you might have a very short spring.

If that’s the case you might need to save your cool season crops, like peas, cabbage, and broccoli, for the fall garden, instead of planting them in the spring and hoping they produce before the heat sets in.

You’ll also want to carefully select plant varieties. Maybe determinant tomatoes would be better than indeterminate tomatoes, or an early producing cucumber instead of one that is later producing?

What is the length of time between your average last frost date and when you normally experience temperatures in the upper 80s or low 90s?

Dealing with High Temperatures in the Garden

Avoid Heat Stroke and Sunburn

Regardless of how many heat days you get, you always want to make sure that you take measures to avoid heat stroke while working outside.

This means:

• drink plenty of water
• limit caffeine
• try to work early in the morning or late in the evening

During the summer months I try to be in the garden by 7am and back inside by 9am. We have a lot of humidity and so even if it’s only 85°F by 9am, the heat index can easily be 10 or more degrees higher.

If I have to go out into the garden during the day “just real quick”, I toss on a long sleeve shirt and hat. It never fails, that when I don’t, I get side tracked and stay out long enough to get a tan. I don’t burn, but I worry about long term sun exposure.

See Heat Stroke – Symptoms, Treatment and Prevention for more tips on avoiding heat stroke and recognizing symptoms.

Growing Vegetables in Extreme Heat

It’s not only people who struggle in high temperatures. Once temperatures reach about 95°F, plants will struggle, even heat loving plants. Most flowering plants will stop flowering and setting fruit. The goal at this point, is to keep the plants alive until the temperatures go down.

Depending on how long your hot season is will determine how many plants you choose to keep alive. If you know you only have a few weeks of temperatures in the 90s or 100s, then you might choose to intensely care for your whole garden. However, if you have 8-10 weeks of temperatures in the 90s and 100s, like I do here in Texas, then you might need to limit the number of plants you can keep alive until the heat subsides.

Because I live in a cold hardy zone 9, I can usually plant a fall crop of things like snap beans, cherry tomatoes, and summer squash. Therefore, I choose to keep only a few of our snap beans and a few tomato plants alive through the heat. Our okra, peppers, and basil do just fine in the heat with minimal care, so I tend to those too.

What you choose will likely be different because your climate and season of life is probably different than mine. I have neighbors that are able to keep their entire vegetable garden alive all summer. However, their garden is smaller than mine and they no longer have children in the home. There’s no right or wrong answer – every gardener needs to make the choices that are best for them.

Watering Summer Gardens

The most important thing you can do for plants in the heat of summer is to water them. Water will cool the plants off and keep them hydrated. I know we all want to see perky leaves on our plants, but try to water the ground and not the leaves. Summer is prime time for powdery mildew and other diseases that flourish in hot, damp conditions.

Most people recommend watering only in the evening to conserve water. This gives the plants time to recover overnight before the heat comes again the next day. However, if you have temperatures over 100°F you might need to water more than once a day. Whenever you water, water deeply; this will cause the roots to continue growing down instead of spreading just under the surface.

The photo above demonstrates a simple homemade irrigation option. Simply sink a container with a few small holes in the bottom into the soil near your plant. Fill as needed to maintain drip irrigation to the roots of the plant.

Mulching to Beat the Heat and Conserve Water

Mulching your garden will help keep the moisture from evaporating, and is essential in the heat of summer. You don’t have to go out and buy mulch; leaves, straw, wood chips, and shredded newspaper all make good mulches. Before adding mulch, be sure to water the ground really well. When you need to water after you’ve mulched, try to put the hose into the mulch so you’re watering below the mulch and not on top of it, if possible.

How much sun is too much sun in the summer vegetable garden?

I know many plant tags or seed packets indicate that a plant needs full sun, but most plants don’t need 8 hours of intense summer sun day after day. So, if you have long hot summers, you can protect your plants by giving them some shade. One way to do this is to plant your plants that you want to survive all summer in dappled shade or where they get afternoon shade.

If you have already planted and your plants are really struggling, you can purchase shade cloth for them. I’ve not used this but every year I say I’m going to try it. The shade cloth will protect the plants from the intense heat, but you will still have to water and mulch the plants.

Set Realistic Expectations for Your Summer Garden

Adjusting expectations the last way I deal with heat in the garden. Every summer we experience 3 or more months of temperatures in the 90s and 100s. I used to get really frustrated that my “summer” garden wasn’t making it through the summer. As I learned more about my climate and began to understand how heat and humidity affects plants, I’ve been able to have a more productive garden by focusing on:

• the right varieties of plants for my area
• deciding which plants I’m going to “baby” to keep alive until temperatures decrease
• watering and mulching properly

This has really helped me enjoy my garden more, even in the dead of summer. Hot weather gardening certainly has its challenges, but hopefully these summer garden tips will give you a good chance of keeping your vegetable garden alive all summer long.

Other gardening posts you may find useful:

• Natural Weed Control – Weed Killers and Non-Toxic Weed Control Options
• Too Much Rain in the Garden – Managing Wet Dirt and Waterlogged Plants
• The Ultimate Guide to Natural Pest Control in the Garden

This is a guest post by Angi Schneider. Angi Schneider lives with her family along the Texas Gulf Coast on 1.5 acres, where she keeps a large garden, a growing orchard, chickens, and bees.

When she’s not in her garden or homeschooling (or chauffeuring) her children, she can be found hanging out and chatting about all things simple living at Rootsy.org.

On her personal website, SchneiderPeeps, she offers a great product called The Gardening Notebook. The Gardening Notebook is custom printable e-book to help you keep track of everything that is important to you in your gardening.

Originally posted in 2017, last updated in 2019.