There is no perfect formula for watering plants. The reason for this is that there are so many different factors that influence how much water plants may need in a particular situation. Water, however, is necessary for plants to live and function. The purpose of this page is to give some helpful advice on implementing a watering program for your shrubs and trees.
The general recommendation usually given for watering is to apply 1 inch of water per week (or ½ of an inch of water twice a week) either by rainfall or sprinkler. A simple rain gauge placed under a sprinkler can show how much water has been given to the plant per irrigation. Watering less frequently in larger amounts according to this rate usually gives better results. Too frequent shallow watering can cause roots to grow shallow, making them more prone to drought damage.
One of the most common reasons for plant death is too much water. Certain trees and shrubs, like spruces and yews, cannot tolerate water-logged soil. On the other hand, the bald cypress and the black gum are both known for being able to tolerate wet soil. The tags that come with the plants will sometimes give the moisture/drainage requirements for the plant.
Some plants can tolerate prolonged periods of drought. Arborvitae and hemlocks, for example, do not tolerate long periods of drought, especially when they are newly transplanted. Other trees, like the little leaf linden and callery pear, are known for being able to handle tough conditions. Knowing the ideal cultural conditions for the plant is important for gauging how much to irrigate.
"HOW DO I KNOW IF I'M WATERING
TOO MUCH OR TOO LITTLE?"
There are general and plant-specific signs that plants give off when they do not have enough water. Unfortunately, the signs for too much water can be the same as the signs of too little water. The reason for this is that the roots will often not transport water to the top of the plant when they are sitting in water (and do not get sufficient oxygen). The question then becomes, "how do I know if I am watering too much or too little?"
Scorched Leaves
If the leaves are wilting or scorching and you are confused about whether you are watering too much or too little, the best place to look is the soil. Dig down 6-8 inches and feel the soil. Does it feel moist? Does it feel cool? Does it feel dry or warm? The soil should be cool and slightly moist but not soaking wet. Squeeze the soil into a ball. Does it hold its shape? If it does not hold its shape, then the soil may not have sufficient moisture (but it is also possible that the soil is very sandy). Try to rub the ball you just made. Does it crumble when rubbed? If the soil is too wet to crumble when rubbed, it may have too much moisture (it is also possible, however, that the soil has large clay content).
Wilting Leaves
With a little practice, you can check the moisture content of the soil quickly. Monitor the rainfall over the course of the growing season with a rain gauge. Observe some of the more water-sensitive plants to know when rainfall has not been sufficient and supplemental irrigation are necessary. Mulch over the root zone of the plants (but not against the trunk) to conserve moisture. Be careful not to use certain mulches that crust over after a while and do not allow water to penetrate them.
Girdling Root
There are other problems that can occur in the landscape that may keep water from entering the roots, or from being transported from the roots to the top of the plant. Insects and diseases can attack roots, restricting uptake of water, or can attack the stem, both of which can result in the wilting of leaves. Nylon string never removed from the top of the root ball, as well as girdling roots, can starve the roots by restricting the flow of sugars manufactured in the leaves down to the roots. This can cause a wilting or browning symptom as well. Planting too deep can restrict necessary oxygen to the root system resulting in water stress symptoms. De-icing salt plowed up on top of the root zone of a sensitive tree, or excess fertilizer, can both pull water out of the roots. Mechanical injury to the bark (from the trunk being hit or from animal injury) can also hinder the uptake of water to the leaves. There may even be multiple causes that work together to result in leaves wilting or scorching.
Mechanical Injury
TIPS FOR WATERING
Here are a few final tips for watering:
• Match up plants with their sun requirements correctly so that they will not need excessive water just to survive.
• Realize that the root zone of a tree or shrub may extend past the furthest branches of the canopy (don't just water next to the trunk).
• Don't water during the hottest part of the day but rather water in the morning or at night.
4.) Avoid sprinkler irrigation that wets the foliage of plants and trees that are prone to leaf spot diseases.
