How to Water Your Trees in a Calgary Summer

Calgary averages only about 412 millimetres of precipitation per year, and much of that falls as snow. During summer, it is common to go two or three weeks without significant rain, especially in July and August. For trees, particularly younger ones and recently planted specimens, this can be a serious problem. Proper watering is the single most important thing you can do for your trees during a Calgary summer.

Why Lawn Sprinklers Are Not Enough

Most residential irrigation systems are designed to water turf grass. They run for short cycles and wet only the top inch or two of soil. Tree roots, however, extend 12 to 18 inches deep and spread well beyond the canopy. A brief sprinkler cycle does almost nothing for a tree. In fact, it can do harm by encouraging shallow root development, making the tree more susceptible to drought and wind throw.

Trees need slow, deep watering that allows moisture to soak down to the full depth of the root zone. This encourages roots to grow deep and wide, creating a stable, drought-resistant tree.

How Much Water Do Trees Need?

A general guideline is 10 gallons of water per inch of trunk diameter per week during hot, dry weather. So a tree with a 4-inch diameter trunk needs roughly 40 gallons per week. That sounds like a lot, but spread over a slow watering session, it is quite manageable.

For newly planted trees in their first two years, the need is even more critical. Their root systems are small and concentrated in the original root ball area. They cannot reach out to find moisture the way an established tree can. Water new trees two to three times per week during summer heat.

The Best Watering Methods

Soaker Hose

Lay a soaker hose in a spiral pattern around the tree starting about a foot from the trunk and extending out to the drip line. Run it on low pressure for 30 to 60 minutes. This delivers water slowly and evenly across the root zone with minimal runoff or evaporation.

Garden Hose on a Slow Trickle

Place the end of a garden hose at the drip line and turn it on to a slow trickle, just barely flowing. Move it to a different spot every 20 to 30 minutes until you have watered around the entire circumference. This is simple and effective, though it requires some attention.

Gator Bags and Tree Watering Bags

For newly planted trees, these bags wrap around the trunk and hold 15 to 20 gallons that slowly seep out over several hours. They are excellent for consistent, hassle-free watering during establishment and are widely available at Calgary garden centres.

When to Water

Water early in the morning or in the evening when temperatures are cooler and evaporation is lowest. Avoid watering in the heat of the afternoon when much of the water will evaporate before it can soak in. Watering in the evening also gives the moisture time to percolate overnight.

Check the soil moisture before watering. Push a screwdriver or a finger into the soil about 4 inches deep at the drip line. If it is dry, water. If it is still moist, wait a day or two. Overwatering can be just as harmful as underwatering, especially in clay soils where drainage is slow. Waterlogged roots suffocate and rot.

Signs Your Tree Is Drought-Stressed

• Wilting or curling leaves: Deciduous trees curl their leaves inward to reduce surface area and conserve moisture.
• Early fall colour: If leaves are turning yellow or brown in July, drought stress is likely the cause.
• Premature leaf drop: Trees shed leaves under severe stress to reduce water demand.
• Scorched leaf edges: Brown, crispy edges on otherwise green leaves indicate the tree cannot supply enough water to the leaf margins.
• Bark cracking: In extreme cases, severe drought can cause bark to split, especially on thin-barked species.

Do Not Forget Fall Watering

The last major watering of the year is one of the most important. Before the ground freezes in late October or November, give every tree on your property a deep, thorough soak. This stores moisture in the root zone that the tree will draw on all winter. Trees that go into winter with dry roots are far more likely to suffer desiccation damage and dieback.

Proper watering takes a bit of time and attention, but it is the most cost-effective tree care investment you can make. A well-watered tree is a healthy tree that resists pests, disease, and storm damage far better than a stressed one.