13 Tips for Gardening in Extreme Heat
Some gardeners live in climates with extremely hot summers, where daily temperatures frequently exceed 90, or even 100 degrees. If this is your situation, summer may be the most difficult season for your garden, instead of winter.
Extreme heat is not only stressful for many plants, but it can actually make many of them go dormant and stop growing – even if they are kept well watered. High heat can also keep plants from setting any fruit because extremely hot temperatures can kill the pollen. Other crops will bolt and go to seed extremely quickly.
Here are thirteen tips to help you continue gardening during very hot weather:
1. Focus on plants that love the heat.
Look for those vegetables that were bred for the desert, the southern states, or the tropics. These include: tomatoes, eggplant, melons, peppers, malabar spinach, cowpeas, and lima beans. Sweet potatoes, okra, and southern peas can handle the most heat.
However, even many of these plants may drop their blossoms and stop setting fruit when the temperatures regularly exceed 90 degrees F. Look for varieties that may have been bred to continue fruiting in extreme heat.
2. Keep your plants well-watered.
Although in some situations you may need to water daily, it's very important to water your plants deeply – a minimum of 6 inches down – at least once a week for clay soils, and twice a week for sandy ones. Don’t guess – check your soil moisture level by using a trowel to dig 6” down.
You’ll gradually learn how much you need to water your garden to maintain a good moisture level. Expect your garden to need at least twice as much water (or even more) during periods of extreme heat. High winds can also increase water demand.
Make sure you don't let the soil dry out too much in between watering. I've had sweet potatoes tubers and butternut squash fruit split badly when the plants were heavily watered after the soil had become very dry.
3. Make sure your soil has a good level of organic matter.
Healthy levels of organic matter (about 5-9%, depending on your soil type and climate) can make a huge difference in helping the soil to retain more water. In addition, a healthy soil full of beneficial soil organisms, such as mycorrhizal fungi, helps plants to better tolerate drought.
4. Keep your soil covered with 2-4” of organic mulch.
Using straw, grass cuttings, shredded leaves, etc. for mulch will keep the soil cooler and prevent it from drying out as quickly – but don't use too thick of a layer. While mulch can help preserve moisture in the soil, a thick layer can also prevent rainfall from reaching the soil underneath, as the mulch itself can absorb large amounts of water.
5. Give your plants some shade.
Giving your garden some partial shade during periods of extreme heat can reduce temperatures by 10 degrees F or more. You can cover your garden with shade cloth, a snow-fence, or latticework supported on a frame – even old sheets or sheer curtains. Make sure your shade-producing materials are well-secured against high winds, and are high enough above the plants so that your garden will get good ventilation.
Many gardeners in extremely hot climates have found that providing about 30-40% shade usually works best. Even tomatoes, peppers, and squashes can benefit from shade cloth in desert climates.
You can also put your garden on the east side of a building, where it will receive shade during the afternoon heat. Some people choose to place their gardens on the east side of trees, tall shrubs, or trellised plants. Just be sure that the roots of the trees and shrubs won't invade your garden and compete with your vegetables. Tree roots can extend far beyond their branches. Even large vegetable plants on trellises can seriously compete for water with smaller plants in the same garden bed.
6. Avoid surrounding your garden beds with crushed stone, brick, or concrete paths.
These will absorb extra heat and continue to release it after the sun sets – the equivalent of the “urban heat island” effect in your garden. Your garden will also be hotter if you place it up against an unshaded south or west side of buildings (in the northern hemisphere). You can keep your garden cooler by surrounding your garden beds with lawn grass or organic mulch.
7. Start seeds indoors under lights
Many seeds will not germinate at all if the soil gets too hot. During periods of extreme heat, one option is to start these seeds indoors under lights, and then transplant them into the garden after hardening them off (gradually adjusting the plants to direct sunlight and wind). Make sure you keep your newly planted seedlings well-watered and partly shaded as they get established outdoors.
8. Pre-soak seeds and furrows for crops you plant outdoors
For your larger seeds (such as peas), pre-soak them for 24 hours before planting them outdoors. Water the seed bed daily to keep the soil moist until the seeds germinate.
For smaller seeds, create your furrows or planting holes, fill them with water, and let the water soak into the soil just before planting your seeds. Cover your seeds with compost or potting soil (which are less likely to crust over in the heat), and then keep the seed bed shaded and well-watered until the seeds come up.
A light sprinkling of dried lawn cuttings on the seed bed will help to shade the soil and keep it moist. You want the layer to be thin enough to still see some soil between the cuttings, so that the mulch won't block the seeds from emerging.
9. Keep ripe fruit well-picked
Ripe fruit (tomatoes, melons, peppers, etc) require large amounts of water from your plants. To reduce heat and water stress on your heavily-producing plants, harvest your ripe fruit frequently and thoroughly (including damaged fruits).
10. Space your plants farther apart
Plants spaced closely together will compete strongly with each other for water. If you are able to space your plants farther apart, they will experience less stress during periods of extreme heat.
11. Keep your garden well-weeded
Weeds usually have much more vigorous root systems than do our domestic vegetables, and they can out-compete with our crops for water in the soil. Do your garden a favor, and keep the weeds out.
12. Avoid using tall raised garden beds, if possible.
Raised beds warm up more, and dry out more quickly – a disadvantage in hot climates. The soil is cooler and moister deeper down in the ground. So, in extremely hot dry climates, I suggest focusing on improving the soil deeper down instead of creating raised beds.
13. Avoid growing large plants on trellises, if possible.
Trellised plants lose moisture much more quickly than those growing on the ground. If, due to space limitations, you need to trellis your plants, it's critical to keep them well-watered and mulched.
By taking advantage of many of the tips listed above, you can continue to garden successfully during hot summer weather!