Do I Need to Water My Trees?

As a Calgary-based arborist, I have enjoyed working for clients throughout Calgary. Given our relatively arid climate, I am always impressed with the substantial urban forest within the community.

A question that customers often ask me is – “Do I need to water my trees?” This seemingly simple question is not easy to answer as there are many variables to consider. To that end, I have provided some guidelines to help answer this question.

Why? – Trees have three basic requirements – sunlight, soil, and water. Without enough moisture, trees cannot survive. To support this valuable community resource, trees in urban environments usually require supplemental watering (more than just rainfall).

• Urban soils are typically shallow, compacted with low water holding capacity
• Heat island effect – urban environments tend to be hotter and dryer
• Dry winds – we live in a wind-prone region.

How Much? – This depends on the current weather, geography, local soil conditions, age, and species of tree, but in general, the following ‘rules of thumb’ can be applied.

Young trees require more care to become established as they have an underdeveloped root system. A general guideline is 2 gallons of water per inch of trunk diameter for the first several years. Mature trees require about 5 gallons per inch of trunk diameter at breast height (4.5 feet).

How Often? – Once a week under normal conditions for both young and mature trees. Newly planted trees have an undeveloped root system; watering twice weekly is advised. Extreme heat/drought (like what we have experienced over the last several summers) may necessitate more frequent watering of trees and shrubs.

How can I tell if I have watered enough?

• Look for signs of drought stress, such as – brown leaf tips/edges, wilting, or premature leaf drop.
• Screwdriver test – can a screwdriver be pushed into the soil relatively easily, or is it difficult? If more effort is required to insert the screwdriver into the ground – the soil is too dry.
• Soil ball test – Take a hand full of soil from several inches deep and try to roll it into a ball (like making a cookie). If you can make a soil ball in your hands that easily crumbles, the soil is wet enough. If you can’t make a soil ball – the soil is too dry. If the soil ball doesn’t crumble and is sticky – the soil is too wet.

When should I water?

• Early morning is the ideal time to water; less sun/wind means less evaporation. Wet vegetation can dry out during the day, which helps to reduce fungal/bacterial disease pressure.

Trees require watering from spring until fall freeze. Trees that are adequately hydrated in the early season are more resilient and more likely to fend off disease and insect attacks and cope with extreme hot/dry spells. Trees sufficiently watered in the fall suffer less cold injury and have more stored resources to resume healthy growth in the spring.  

How do I water my trees?

• Trees should be watered in a manner that provides needed hydration and assists in developing a healthy root system. This requires a periodic (weekly) long deep soak, unlike grass/sod, which is usually watered 2-3 times weekly for short intervals.
• For young trees watering should be concentrated at the root ball and just beyond.
• Watering mature should be concentrated in a zone approximately 5 feet from the trunk outwards to the dripline and beyond.

A couple of watering NO – NO’S:

• Directly spraying high-pressure water at a tree trunk may damage vascular tissue inside the bark.
• Directing a hose/eaves trough downspout at the tree’s base may lead to trunk rot and contribute to wind throw in windy environments.

Too much of a good thing is not good, so be sure not to overwater your trees. If the ground near your trees seems saturated, reducing the water amount applied is advisable.

If you have questions or concerns about your trees – be sure to give us a call!