The summer of 2016 was one of the driest on record in southern Ontario. This, after a winter of little precipitation, resulting in a trifling amount of snow melt.
The effects of drought are seen immediately in some plants, while others struggle through with signs of stress coming much later. Needy annuals in containers will show signs of stress first. They wilt, leaves turn yellow and then brown, and flower production stops. Sometimes they bounce back with a good watering, other times not. They are our canary in the coalmine, revealing to us immediately their need for water.
Some perennials, too, will show signs of water stress quickly. Phlox and ligularia will wilt, and the leaves of ostrich ferns and astilbe will dry out and turn brown. Hydrangeas suffer, showing shrivelling leaves, and later, smaller flowers. But unless we have these bell weather plants in our garden, showing us the effects of dry conditions, we forget about the big guys, our workhorse woody shrubs and trees, toughing it out, not revealing the stress they are under until much later.
This summer we saw leaves on trees turn brown in September, weeks before they would typically have shown their autumn colours. We see small branches on shrubs and trees losing their leaves and dying, branches that are brown underneath their bark, indicating they’re dead and need to be removed.
We may see smaller buds on spring flowering shrubs, larger branches fail to leaf out next spring, and insects and disease moving in next summer.
Cedars, touched not only by drought, but by the relentless heat this summer, are showing yellow and brown.
A general rule for watering trees during a drought is 1”-2” of water every week. Putting out a flat bottomed container to catch water is a good way to measure how much your tree is getting.
There are many factors that go into how much and how often you water. Soil type and whether or not there’s grass under the tree canopy are two of the most important considerations. Clay soil holds water more than sandy soil. And trees with grass under their canopy will need more water than trees with bare earth or mulch underneath. As always, the best time to water is early morning.
We’ve had two good days of rain this week. Everything needs it. But remember, the season of watering is not over. Deciduous shrubs and trees will continue to need water until they drop their leaves. Coniferous trees need water right up until the ground freezes.
And remember next spring that if there’s little or no snow melt, trees and shrubs will need water as soon as the ground thaws, and will continue to need water right through the spring, summer and fall, whether from rain or from your favourite sprinkler or soaker hose.