Making sure your plants get the water they need would seem to be a simple enough proposition, assuming you know how to turn on a faucet.

But there are some basic principles around irrigation that govern how effectively you use water, and how efficiently your plants can make use of it. And with so many drought-prone regions in North America restricting the amount of summer water available to lavish on gardens, it’s important for each one of us to conserve this precious resource.

Forget the 5-Minute Sprinkle:

I cringe when I see someone strolling across a parched lawn, usually in mid-afternoon on a blazing hot day, waving the hose back and forth while barely wetting the surface of the grass. According to turfgrass experts, this kind of shallow irrigation is worse than none at all since it tricks grass plants into sending small feeder roots up to the surface of the soil. Without continued watering, these thirsty little roots are left high-and-dry to die.

So the rule of irrigation to promote deep rooting is to leave the sprinkler or hose running long enough in one place to deliver a good soak – about 1 inch a week if there’s been no rain. If you don’t know how to measure that, put a container on the lawn and time how long it takes to fill it to the 1-inch (2.5 cm) line.

The best time to water is in early morning; the worst time is in midday heat, when much of the spray evaporates. Occasional night-time watering is fine too, but plants such as phlox and monarda that are prone to mildew are more likely to develop it when their foliage is allowed to remain wet all night.

Help for Containers That Dry Out Quickly:

Whereas garden soil holds moisture for relatively long periods, exposed containers on decks or balconies tend to dry out quickly on hot days.

I’ve discovered two remedies for this problem. First, I use a soil-less planter mix containing water-retentive polymers that absorb rain or irrigation water, then release it slowly into the soil. (One caveat: this type of soil works well in hot-summer areas, but might be too moist for typically rainy areas like the Pacific Northwest.)

Second, I discovered a fabulous line of clay-look, resin planters manufactured by Bemis in Wisconsin. They incorporate a controlled watering system utilizing a raised ventilated platform that creates a pocket of air between the plant and the water reservoirs, or “soil-sipping columns”, at the bottom of the pot. There’s an overflow hole a few inches up that prevents too much water from collecting and rotting the plants. I’ve been able to reduce my watering needs considerably with these planters -- I even have a thirsty mophead hydrangea in one and I rarely have to give it more than one watering a week – but find that the larger containers work better than the small ones.

Use a Mulch to Conserve Water:

A thick summer mulch will keep your garden soil weed-free, while preventing it from drying out. Use shredded bark, seed-free straw, or a leaf mulch made from leaves raked saved from the previous autumn – plentiful and absolutely free!

Install a Drip-Irrigation System That Waters Slowly and Efficiently:

For garden borders, simple soaker hoses are more efficient than sprinklers, using 30-50% less water and delivering it slowly through tiny holes to the base of plants – or to the root zone itself, if the soaker hose has been buried in the soil. You can even install an electronic timer for a totally hands-off operation. More complicated in-soil, drip-irrigation systems with sub-mains and emitters are also available, but may require help to install.

Water Trees & Shrubs Drop by Drop:

For smaller trees and shrubs, rather than trying to water them with a sprinkler or running the hose at their base at full force, which can result in wasteful run-off, turn the hose on to a rate of 15 drops per 5 seconds, then leave it in place for a period of several hours. Slow watering like this encourages complete absorption by the soil. Another idea is to punch a few nail holes in the bottom of a 5-gallon bucket, then fill it with water which will drain very slowly. If desired, a soluble fertilizer can be added at this time too.

Mature shade trees, by and large, are at the mercy of the (rain-and-snowmelt-dependent) water table well below your garden soil. But in periods of extreme drought, some experts recommend alleviating stress on the roots by giving valuable trees a deep soak – 2-3 inches a week – over 50% of the area covered by the tree’s drip-line (the area under the extended branches). This should result in a soaking to the top 12-18 inches of the soil. Don’t pour the water on quickly, since much of that volume could run off; instead, spread it over a few days.

Harness Rainwater From Your Roof:

Some enlightened cities have banned downspout connections to the sewage system. Why? In heavy rains, combined storm/sewage pipes tend to overflow, bypassing water treatment plants and polluting lakes and rivers. By disconnecting your downspout and either directing the flow of rainwater into the garden or into a rain barrel with a spigot, you take full responsibility for your own patch of paradise – and get a free supply of rainwater to boot!

Plant Drought-Tolerant Species that Reduce the Need for Irrigation:

Finally – and most importantly -- if you live in an area where drought has become a serious issue, you need to think about changing the way you garden. That means choosing trees, shrubs and herbaceous plants that require less water. There is lots of information on the internet, in reference books, and at your local Ministry of Natural Resources or Extension Agent on the best drought-proof plants for your area. Best of all, they’re often attractive and easily-acquired native plants that are acclimatized to the very conditions your thirsty garden plants might be struggling to cope with. Read about 30 great perennials that like dry conditions.

Adapted from a column that appeared originally in the Toronto Sun

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