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GardenSMART :: Fending Off the Fahrenheit - How to Beat the Heat In Your Vegetable Garden

Fending Off the Fahrenheit - How to Beat the Heat In Your Vegetable Garden

By Joan Casanova, Bonnie Plants
Photographs courtesy of Bonnie Plants

Temperatures are rising and high heat can wreak havoc in the vegetable garden. When temps climb to the upper 80's and sometimes soar into the 90's and 100's, plants need some assistance in fending off the Fahrenheit.

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Here are some helpful hints when heat is high:

Combating insects: It's best not to apply horticultural oils to combat insects when temperatures rise into the upper 80's and above 90 degrees. Horticultural oils can burn foliage and scald fruit before harvest. If you spot insects, try using a horticultural soap, or water-jet them off the plant and repeat until there's no sign of them. Or pick the bugs off the plant and drop them in a bucket of soapy water. Insecticides can be used, but be sure they're labeled for edibles!

Fertilizing Plants: Your plants aren't absorbing much in the high heat. Too much fertilizer can burn tender plant tissue, and stunt plant growth.

Water wisely: Once the temperatures begin to soar you'll need to provide your plants with plenty of water. It's best to give the plant roots a deep soaking so water deeply. Soaker hoses or drip irrigation work well, but if you don't have a water system in place, use a hose, water deep at the soil line and skip watering the leaves of the plants.

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There's a tendency to overwater plants in hot weather since the topsoil dries out so quickly. Stick to giving your garden about one inch of water at a time. Plants should be watered deeply when the top two inches of the soil becomes dry to the touch. To test, just stick your finger or a pencil about two inches down into the soil. If the soil is dry, it's time to water, if wet, wait until the soil is dry. Be careful not to overwater, as overwatering can cause problems, such as root rot, especially in containers or raised beds.

Continue weeding: Weeding is a chore that must be continuously practiced. In high heat, removing weeds reduces competition for the limited moisture and nutrients in soil.

Use much mulch: Use mulch, mulch and more mulch around the base of your vegetable plants. Mulch helps to conserve moisture, which can be critical for the life of the plant. It also keeps weeds down and shields the soil from direct sunlight, which can cool the soil temperature by five to ten degrees.

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Mulch will also keep soil from splashing up on foliage, which can prevent some soil borne diseases. When it rains, and/or when you manually water, soil bacteria can be splashed up and onto the leaves and stems of your plants. Furthermore, muddy leaves cannot breathe.  

The thicker the layer of mulch you use the better it helps to protect the plants. Using a three to four inch layer will provide a good source of protection from high temperatures. Organic mulch such as straw, leaves, or compost will also slowly break down and add organic matter to the soil.

Feed with Compost: Many vegetables begin fruiting just when the hot weather hits. Because of this, it's prudent to keep them well fed. A good way to feed your vegetables is to use ample amounts of compost. Side-dressing your plants with compost won't burn them like fertilizer and will help supply essential nutrients your plants need during high temperatures.

Supply some shade: Providing some shade to your vegetables during the afternoon – the hottest part of the day – can go a long way towards keeping plants healthy. The best sunlight for your plants is morning sun. The sun isn't as intense and much softer during the morning hours.

You can use shade cloths (available at most garden retailers), which keep the soil and air temperatures cooler – sometimes even as much as 10 degrees cooler. Shade cloths will also help protect foliage from extreme sunlight and reduce the loss of moisture, too. Be sure the plant receives morning sun prior to utilizing shade cloths. Beneficial insects such as bees are most active during the morning hours, so they'll still be able to pollinate plants prior to the utilization of shade cloths.

You can also use an old bed sheet strung up on poles to block the direct sunlight. Any shade cover should be lightweight and light colored to reflect light instead of absorbing it.

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Be prepared for temperatures on the rise: It's a good idea to be ready for hot temperatures in your garden by having the mentioned items on hand. It's difficult to predict what type of weather you may have from one season to the next.

Being prepared for possible high temperatures will give you the ability to reduce its effects quicker. The above methods are not a 100% guarantee your vegetable garden will survive intense heat, but they are solid precautions to take.

For more information on vegetable, herb and fruit gardening please visit


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