Watering trees is easy when you know where and when to do it. With an extremely hot, dry summer as we have had in 2017 applying water is necessary but doing it correctly will help your trees through the drought and help reduce the amount of water that needs to be applied.
When watering landscape trees we are faced with two basic scenarios. We are either supplying supplemental water to mature or established trees, or watering recently planted trees.
Watering Established or Mature Trees
Where to Water
When watering don’t focus on the area directly adjacent to the trunk. This is because there are not generally any roots capable of taking up water in this area and it can cause issues if the trunk is being impacted by a pressurized spray repeatedly or if the trunk is constantly wet. Roots extend far beyond the edge of the tree’s canopy or drip line. Many tree roots extend as far away from the tree as the tree is tall (A 50 foot tree would have roots extending 50 feet from the trunk in any given direction). Areas that are paved or covered by other hard landscape features will not absorb water so it should be applied where it can easily penetrate into the soil. Water in the outer half of the area inside the drip line and beyond the edge of the drip line (to the distance of the height of the tree).
How to Water
You can apply water effectively using sprinklers, drip irrigation, or a hose running on the soil surface. Regardless of how you apply the water, follow these basic rules:
- Apply in the evening or early morning. Trees take up less water in the hottest parts of the day as they are preserving the water already in the tree. They do this by closing pores in the leaves that allow water to be released as gas. This in turn slows the rate which water is pulled in by the roots. Watering when things have cooled down reduces waste as water is not evaporating as fast while it is being applied and makes it available in the cooler parts of the day which ensures the tree is able to take up as much as possible.
- Apply water slowly. Think low intensity and longer duration. This helps to reduce or eliminate any run-off and allows the water to percolate deeper into the soil. This means that you can only water as fast as the soil allows the water to penetrate it’s surface and work it’s way down. No run-off = no wasted water
- Stop watering when runoff starts. Soils high in clay (like here in Calgary) accept water slowly, often as little as 1/4 inch per hour. If water starts to pool or run off, stop watering, let it soak in, and start again. Repeat this cycle until you apply enough water to moisten the soil to 24-30 inches. This may take a number of cycles over several consecutive days.
- Water deeply rather than frequently. A good deep watering should moisten the soil to a depth of 24-30 inches. The duration of the watering will change based on the type of soil the tree is growing in. Because most tree roots are found in the upper 8 – 24 inches of the soil profile, this is the zone that should be watered in each cycle.
- Deep watering will meet a tree’s water needs for between 14 days to a few weeks during the hottest part of the summer, depending on the tree species and type of soil. Watering deeply also helps to make trees more tolerant of drought as the roots will grow into the soil deeper down. This soil dries out more slowly than the surface, more moisture is available to the tree for a longer period of time when it has a deeper root system.
- Before starting a new watering cycle, it is important to check the soil to see that is has begun to dry out. However you don’t want it completely drying out between watering cycles.
- Watering can be reduced or skipped if there is a long, slow rain. However most of our local thunderstorms produce a huge amount of water in a short period of time. Most of this water does not have time to penetrate the soil and ends up running off into our sewer system.
- Mulching the root zone of a tree with wood chips has many, many benefits but the biggest one is the reduction of water lost through evaporation. Mulch helps hold the water in the soil which reduces how much water a tree needs and how often it needs to be applied.
It is important to water throughout the growing season during any dry periods. Usually in Calgary it makes sense to water from May through August. In September, if it is very hot and dry, some watering can be done in the first two weeks. However, the tree will need to shut down and get ready for the cold Winter ahead. Stop watering in early to mid-September to allow the hardening-off process to take place.
Once the leaves have come off in the fall, the tree is no longer using or taking up much water. It helps to deeply water in your trees towards the end of October, just before everything freezes up. This will ensure there is available water for the tree as soon as the soil starts to thaw again in the Spring.
Watering Newly Planted Trees
Watering newly planted trees correctly is very important in determining whether a new tree will survive. New trees have either lost a significant portion of their root system when harvested (Caliper Trees) or the root system was cut or damaged when planted (Container trees). This means that the tree has fewer feeding roots to pull up water and feed the tree until the root system can recover and replace those lost roots.
Where to Water
When watering new trees you want to water directly under the canopy and into the root-ball. The area just outside of the edges of the hole should be watered to encourage roots to grow out of the initial planting hole.
How to Water
Give the tree enough water to meet it needs and nothing more. By keeping it a little on the dry side we encourage the roots of the tree to seek out moisture in the area outside the initial hole and establish its new root system. However it is important to not allow the soil to dry out completely as a new tree will not survive long because of an insufficient root system. Clay soil is heavy, a hole dug in clay acts like a bowl that holds water. It is important to check that the soil is draining and drying a bit between watering cycles.
The Initial Watering
Once you have planted your new tree the initial watering rehydrates the tree roots and supplies the surrounding soil with moisture. It also helps to remove air pockets from the soil which can dry out roots and help bring the roots and the soil particles into contact.