Watering Plants

Why should I water my plants?

Too much water and not enough water are the two leading killers of trees and shrubs. Keeping your trees and shrubs vigorous and healthy is half the battle in repelling insects and diseases. A large part of your plants’ health depends on them receiving the proper amount of water. Improperly irrigated plants are typically hurt before they show external symptoms such as wilting and yellowing.

When should I water?

All plants should be watered from spring to fall. If mother nature is not providing weekly soaking rains then you should step in and take over. As a general rule, mature trees should be watered once a week and younger trees and shrubs should be watered every three days. Allow the soil to dry somewhat between watering. This allows oxygen to be absorbed more easily. Use a soil probe or your own version consisting of a thin metal rod. If you can push the probe fairly easily into the soil but meet resistance at a depth of about 4 to 6 inches, it’s time to reapply the water. Bear in mind that this is a rule of thumb.

How should I water?

Avoid frequent light watering. This applies especially to people who have an installed sprinkler system (see below). Frequent light watering promotes the development of shallow root systems that are susceptible to winter injury and summer heat stress. Water infrequently but deeply (at least 6 to 8 inches) and allow the soil to dry out some between applications. Most tree roots are not very deep (within the upper 6 to 12 inches of soil), and deep roots will receive water if enough is applied to the soil surface. Again, be careful not to overwater established trees and avoid applying water directly to the trunk.

Water with an open-end hose at a rate low enough to keep the water from running off. A quick rule of thumb for watering trees is to water one hour per inch diameter of the tree. When you’re watering trees, remember that much of the water will be absorbed by the roots at or beyond the drip line, not at the base of the trunk. The root system of a mature tree can spread out 1 to 3 times the width of the canopy, so that’s the most efficient area to give your trees a drink.

When it comes to newly planted or young trees that have yet to attain much of a canopy, water needs to be applied closer to the trunk area. New trees need more water than established trees. As the tree matures and the canopy spreads, widen the watering area. Once a tree is established, reduce the frequency of watering.

Best time to water: Early morning or evening, so that less of the water will evaporate in the midday sunshine. If you’re watering in the evening, avoid watering the foliage as this can promote the formation of mildew and fungus. Don’t flood ‘em! If you pour on too much water too fast, you’re only adding to the problem. You can cause erosion and compact the soil, as well as wasting valuable water. Never apply water faster than it can be absorbed by the soil.

I have a sprinkler system. What does this mean for my trees?

Sprinkler systems work wonderfully for turf and flowers. However, when it comes to trees and shrubs, sprinkler systems do not provide adequate irrigation during periods of drought and heat. As mentioned above, they tend to promote shallow root systems that are even more susceptible to the negative effects of drought. Further, these systems typically keep leaf surfaces wet and this promotes leaf fungus and leaf scald. When it is hot and dry it is best to think of your irrigation system as supplemental watering. They do help keep trees and shrubs hydrated and they help to keep soil temperatures down but they do not typically water tree root systems.