What to Do When Your Garden Gets Too Hot

A sudden run of 98°F to 105°F weather is different from an ordinary warm week. The goal is not to make every vegetable grow through it. Protect the plants and harvest already on hand, then let the garden slow down until nights cool.

Start with what can fail in an afternoon. Small containers and young plants have very little reserve. Established tomatoes and squash can look rough without being finished, especially when they still have a full canopy and new growth at the center.

Move portable containers into afternoon shade before the heat arrives. Dark plastic pots can heat the mix along their sun-facing side, so shade or screen the container itself as well as the leaves. Fabric grow bags stay cooler, but their breathable sides make them dry faster. Water a container until water drains from the bottom, then check it again late in the day. In a severe heat wave, a small pot or grow bag may need a second watering.

A potting mix that has dried and pulled away from the container can shed hose water down its sides. Set that container in a shallow tub of water for 20 to 30 minutes, until the mix has wicked up moisture, then lift it out to drain. Do not leave an ordinary pot or fabric bag in standing water for the duration of the heat wave. A self-watering container is different because its reservoir is designed to hold water below the root zone.

Water trapped in a hose lying in direct sun can be far hotter than the water coming from the tap. Run that first hot water onto a path or other non-planted spot until the stream feels comfortably cool. Then aim it at the soil, close to the plant.

Morning is still the easiest time to water a bed well, but heat does not make a dry container or shallow-rooted bed wait until tomorrow. Water it as soon as the soil at the base is dry. The old warning that water droplets act like magnifying glasses is not a reason to leave a thirsty plant dry. Keeping water off the foliage mainly reduces waste and the time leaves stay damp.

Set a supported 30% shade cloth above plants that have suddenly lost leaf cover. Leave enough room for air to move beneath it. A cloth resting directly on hot foliage will not give the same protection.

Keep healthy tomato and pepper leaves in place. Their canopy is the first defense against sunscald. A tomato showing its first pink or pale blush has reached the breaker stage. At that point it can finish ripening indoors with full flavor, so picking it before a brutal heat spell is reasonable. Fruit left exposed on the vine may stall or develop sunscald.

Do not prune hard or transplant during a heat wave. Hold fertilizer until the weather eases. Each job asks the plant to recover or make new growth when it is already trying to conserve water. Pull weeds when you can do it safely, since they compete directly with vegetables for moisture.

Hold horticultural oils and sulfur products for a cooler window. Treat 85°F as a sensible stop point for them in a vegetable garden, especially on plants already stressed by sun or drought. Some labels set a lower limit, and Extension guidance warns that many treatments can injure plants once temperatures stay above 80°F. That scorched or browned spray injury is called phytotoxicity.

Tomato and pepper flowers can drop during hot days and warm nights. Cucumbers and squash may make more male flowers while bees are less active. That flush may be lost, but a healthy plant often sets flowers again after the weather moderates.

A plant with crisp leaf edges or curled tomato leaves may be reacting to heat, not a virus. Give it a few cooler nights before deciding it has failed. A bolted lettuce plant will not become tender again, but it can remain briefly if its canopy is shading a smaller neighboring crop. Remove it once that shade is no longer useful.