Now that temperatures are up in 80's and everyone is hurrying to get trees and shrubs planted before the summer heat sets in, it's a good time to review proper watering. The important thing to remember is that once a plant is showing signs of drought stress, other processes are occurring within the plant that can damage the long-term health of the plant and reduce growth, so ideally plants should be watered before they show physical signs of stress. However, at the same time, over-watering can cause just as much damage by reducing root growth, or even killing the roots, and eventually the entire plant.
So how do you know when it's time to water? You have to check the soil!
Here are a few methods for checking the soil moisture content:
- Gather up a handful of soil and try to press it into a ball. If it just crumbles, the soil is too dry to supply water to plant roots.
- Use a soil probe to pull a sample from the ground near the plant roots to visually check the level of soil dryness. You should be able to see mostly moist soil that is darker in color with a small amount at the very top that will be much lighter in color and dry to the touch. This will give you a good idea of how much you should water. You can also use a soil probe after you have finished watering to check if the moisture has reached the root zone.
- For planters or annual beds, the soil should be soft enough that you can check the moisture level by sticking your finger down 2-3 inches. The potting soil should feel cool and damp.
If plants are displaying symptoms of drought stress, it is important to get them watered deeply as soon as possible. Drought stress can cause long-term health issues and death, resulting in expensive losses in the landscape.
Drought Stress Symptoms:
- Foliage develops a gray cast
- Wilting of leaves and young twigs
- Upward curling or rolling of leaves
- Yellowing and browning of leaves, particularly along leaf margins and tips
- Under-sized and off-flavored fruits, vegetables and nuts
- Under-sized leaves; limited shoot growth
- Blossom and fruit drop
- Interior needle and leaf drop on conifers and evergreens
- Iron chlorosis symptoms on foliage (leaf yellowing between veins)
- Spider mite infestations
Long-Term Problems Caused by Drought:
- Increased susceptibility to attack by insect borers
- Increased susceptibility to certain plant diseases
- Root death
- Terminal dieback; dead twigs and branches
- Diminished winter hardiness
- Eventual plant death
A good rule of thumb is to apply 1 gallon of water per square foot of root zone once a week. This will vary depending on soil type, the type of plant, and its growth stage. New plants require more frequent water than established plants, and sandy soils lose water content more quickly than clay soils. Check new plants daily during hot weather! Checking once a week for the first year is a good idea for trees and shrubs.