The master gardener: Water vital to hot plants
What a strange growing season we’re having this year – temperatures in the 90s as early as May, a serious heat wave before mid-July that produced record temperatures over 100 degrees and more hot weather still to come.
As we swelter and get too hot and dehydrated, so do many of our garden plants.
It isn’t just the air temperature that affects plants. As air temperatures rise, so do soil temperatures. Generally, we’re pleased when soil temperatures finally start warming up around here because until they do, most of our garden plants don’t grow much.
But with extreme heat, the surface temperature of the soil can jump well above 100 degrees and damage plant tissue that the soil touches.
Since soil touches plants at the base of the stem, damage looks a lot like the damping-off of spring seedlings, a fungal disease. In extremely hot weather, though, the damage is caused by heat burning the stem tissue.
Providing shade from the hottest afternoon sun and mulching with 2 to 3 inches of organic material will keep the soil cooler and conserve soil moisture, thus helping garden plants survive the heat.
Check soil moisture frequently during hot spells and watch for signs of heat stress in plants.
Those include scorching of leaf margins, leaf curl and tip burn of leaves.
Water thoroughly and deeply, and water beyond the plant canopy because most of the feeder roots extend beyond the foliage.
Newly planted and young plants are particularly vulnerable because their root systems are not fully established. Deep watering encourages their roots to grow deeper so they are not so dependent on a shallow water supply.
Container plants also are at a disadvantage during heat spells. The pots and the soil heat up quickly; smaller pots heat up faster than larger ones.
If possible, move pots out of the fiercest direct sunlight, and when watering, let them soak up water from below.
Setting a pot with growing plants inside another (perhaps more decorative) pot also will keep container plants cooler.