Garden Plot: Taking care of your plants on hot days

I’m looking at the 10-day forecast, and we are about to have — or are already having — our first prolonged heat wave of the season. And while sun-seekers love to bask in the hot weather (it helps melt away the icy pain of March), plants not so much.

If you’re still installing plants in your landscape, do so in the early evening and not first thing in the morning. All plants suffer a little “transplant shock” right after they go into the ground; and plants that are then subjected to a day of scorching heat are often stressed to the point of injury.

Installing plants in the early evening gives them a good half-day to get established before they have to take the heat.

No matter what, water each plant individually after it goes in, ideally by letting a hose drip slowly at the base for a half-hour. Do not wet the leaves of your plants, especially in the evening.

Early heat waves call for extra attention

The 10-day forecast not only predicts a run of really hot weather, but hot weather without any noticeable rain. And all of our newly planted veggies and flowers are still very small, which means that they can’t hold a lot of water yet. And this is the stage in their lives when they’re most vulnerable to stress. So it’s time for a wise-watering reminder.

The best way to water any plant — tomatoes, peppers, flowers, shrubs and even your lawn — is slow and long. Short bursts of water — anything under a half-hour — may not even be absorbed by your plants.

Later in the summer, when the plants are bigger and can hold more water, the rule is one deep, long, soaking a week. But in this early heat wave you can — and should — water (wisely!) two or three times a week.

A caution on containers

A run of hot weather without any noticeable rain means we have to pay special attention to newly- installed plants.

  • Young veggies and flowers can — and should — be watered deeply (that’s a half-hour or longer) several times a week.
  • Same for plants in large containers made of wood or hard plastic.
  • Terracotta containers and small plastic pots might need to be watered daily. Feel their weight; if they’re light, they’re dry. If heavy, they’re saturated.
  • Always water slowly. Give each container a little water and then take a break; then a little more water. Repeat this until water runs out the bottom.
  • Hanging baskets made of peat moss or coir should be watered six times a day — eight if they’re in full sun. (I’m only half kidding here, kats and kittens; these hanging baskets look lovely, but they dry out FAST.
  • Newly installed trees and shrubs also need extra care in this early heat wave. Immediately after planting, let a hose drip slowly at their base for several hours. Repeat this every other day until we get rain.

When to water

On hot days, always water deeply, for at least a half-hour and ideally much longer.

  • Water in the morning, especially if you’re using an impact sprinkler or anything else that will wet the leaves of your plants.
  • Never water in any fashion during the hottest times of the day; your plants will be closed up tight to maintain the water they already have inside and won’t open up for more until it gets cooler. Watering in the middle of a hot day is a total waste.
  • You may water in the evening if you have drip irrigation or are hand-watering your plants at the base, but don’t wet the leaves.
  • After the heat wave breaks, the rule is 1 inch of water a week, delivered long and slow.

Support your local lawn

During a heat wave, it’s important to protect your lawn. Here are some tips.

  • Only mow when the grass is dry. If you’re lucky enough to have a lot of dew, mow in the early evening, when the dew is gone.
  • It is critical that you not mow lower than 3 inches; your lawn needs to be at least that height for efficient water storage.
  • ALWAYS leave your clippings on the lawn; do not bag or otherwise reuse them. They’re 90% water, which your lawn needs right now.
  • Do not apply — or let a service apply — chemical fertilizers, herbicides or pesticides during a heat wave. They’re never a good idea, but an especially bad one when the temps are hot and the air is dry.
  • And finally, only water your lawn in the early morning, ideally ending just as the sun begins to dry out the grass blades.
  • Never water your lawn more than once or twice a week or you’ll stunt the root system. Set a timer to start watering at 4 or 5 a.m. and to end around 8 or 9 a.m.

Mike McGrath was editor-in-chief of ORGANIC GARDENING magazine from 1990 through 1997. He has been the host of the nationally syndicated public radio show “You Bet Your Garden” since 1998 and WTOP Garden Editor since 1999. Send him your garden or pest control questions at

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