I frequently see gardens that are under-watered in Toronto; I rarely see problems with too much watering. Toronto summers (June-August) tend to be very hot and dry. Also the numerous mature trees in most downtown neighbourhoods, mean that it is important to water our gardens.
My basic rule of thumb is to water twice a week for 2-3 hours in June, July and August. This sounds like a lot to many people and I often hear the concern that this is wasteful: WATERING THE GARDEN IS ECOLOGOCICALLY BENEFICIAL. Unlike some other municipalities in Southern Ontario, Toronto does not have water shortages! The city draws its water from the lake, not from ground water. Associated costs are related to energy use, not water availability. Gardeners are not wasting resources when they water their plants, they are actually benefiting the environment.
Benefits of Watering the Garden:
Plants will transpire the water they take up, releasing it into the air and thereby cooling the ambient air in a natural process of air-conditioning. One mature tree can cool the ambient air by 5 degrees C by transpiration, day and night, apart from the obvious cooling benefits of its shade in the daytime. All plants do this transpiration cooling. If you use air-conditioning in your house or car, this mechanical (rather than natural/biological) form of cooling is using more energy resources (burning fossil fuels or nuclear) than watering your plants will use. Therefore if you want to conserve: turn down or turn off these wasteful technologies first. To cut down on your plants’ water needs in the garden, you can adjust the growing conditions in your garden: add 3″ of mulch around the root zone (but not touching the stems or leaves). Do this every year and the soil itself will become more water-retentive. This added organic matter will improve the health of the living infrastructure around you, reduce harmful water run-off, and ultimately reduce reliance on watering.
Please: Be kind to your perennials, shrubs and especially your trees. They are giving their gifts generously! They deserve our support. Water them in hot spells.