The amount of water a plant needs depends on many factors, including age and species, the time of year, weather and soil type. As a rule, newly planted trees & shrubs require more frequent water than older, more established trees & shrubs. During periods of extended hot and dry days, all trees & shrubs benefit from supplemental watering, even the ones deemed drought-tolerant.
Watering Newly Planted Trees & Shrubs
For the first several months after planting, most of the roots are still within the original root ball. The root ball and the surrounding soil should be kept evenly moist to encourage healthy root growth. After a few months, expand the watering zone to cover the entire area under the canopy. It can take two or more growing seasons for a tree or shrub to become well established. It is vital to provide supplemental moisture in the early years. During hot, dry weather, newly planted trees & shrubs may require water as often as 3 times per week or more.
Watering Established Trees & Shrubs
When watering established trees & shrubs, provide a deep, soaking irrigation to the entire area beneath the plants’ canopy and extending several feet beyond the canopy’s drip line. You should moisten the soil to a depth of 10” each time you water. To prevent rot, don’t apply water to the area directly around the trunk or base
Know When to Water
The easiest way to check soil moisture is to take a screwdriver (8” plus) and poke it into the soil. It will pass easily into moist soil, but will be difficult to push into dry soil. If you can not poke the screwdriver in at least 6” easily, it’s time to water.
How to Apply Water
Soaker Hoses • An excellent way to water trees & shrubs because they release water slowly. Encircle the plant with a soaker hose and run it for an hour or more. As long as it takes for the water to penetrate 6”- 8” using the screwdriver test.
Tree Watering Bags • These are helpful for small, young trees to establish their roots and get off to a healthy start. They prevent overwatering and under-watering, both of which can damage a new tree.
Bubblers • These hose-end devices reduce the velocity of water so it soaks in rather than runs off. Because a bubbler only water some spots at a time you may need to move it around.
Overhead Sprinklers • While these may be the easiest, they can also be the most inefficient for trees & shrubs as half the water is lost to evaporation. Trees & shrubs are better served by slow watering methods right at soil level. It may take several hours to properly water the trees & shrubs.
Frequently Asked Questions
How much water does my plant need?
Apply enough water to moisten the soil to a depth of 10” or more for mature trees & shrubs. A common mistake is to apply frequent shallow waterings that don’t soak deeply into the soil.
My irrigation system waters my lawn regularly. Isn’t that enough for my trees & shrubs?
Probably not. Most irrigation systems are programmed to apply frequent, shallow waterings. Trees & shrubs do better with less frequent but deeper soakings. A heavy soaking once per week is much better than shallow watering every few days. Shallow waterings encourage roots to remain near the soil surface where they are prone to drying out. Watering deeply, encourages deep, drought-tolerant roots.
Should I mulch under my trees & shrubs?
Yes, grass growing under trees & shrubs will intercept much of the water you apply, keeping it from reaching the plants’ roots. It is best to keep a large (3’ plus), turf-free circle around the trunk or base. A 2” to 3” layer of organic mulch, or bark mulch helps conserve moisture and keeps the weeds at bay. Be sure to keep the mulch away from the trunk to prevent rot.
Should I fertilize during drought?
No. drought-stressed trees & shrubs should not be fertilized. When water supplies are limited, trees & shrubs naturally slow their growth. Applying fertilizer can encourage a flush of growth that causes the plant to require more water than is available. Salts in many of the fertilizers can harm drought-stressed roots
Minimize Tree Stress During Extreme Heat
- Avoid digging under and around trees so you don’t disturb the roots
- Don’t do any heavy pruning. It is OK to remove broken, dead, insect-infested or diseased branches.
- Keep an eye out for insect pests and disease. Drought stressed trees are more vulnerable to attack
- Avoid using high nitrogen lawn fertilizers under trees, and never use weed-and-feed products under trees as they can cause harm to the roots.
Even if your area imposes watering restrictions, it’s likely you will be able to properly water trees. If you must choose between trees and turf, remember that trees are a much bigger investment. It will take years, if not decades for a newly planted tree to take the place of a mature tree that has been lost.