We all know that water is an essential element of life, but when it comes to gardening and plants, the subject of water generates lots of questions. Gardeners are always concerned about how much water is enough or too much, when to water, how to water and more. What seems like a simple subject can become complicated. More plants are killed by water problems than by insects, diseases or any other single problem.

Is There a Quick, Easy Answer?
We wish there was a magic answer that would help everyone, but their isn't. How much water a plant will need varies greatly as to type of plant, whether or not it is established or newly planted, the time of year, the weather conditions, the wind, the soil type, the soil drainage and more. For instance, the basic directive for established landscape plants is that they will need an inch of rain every 2-3 weeks. If you follow that guideline, the plants should do okay. But that may be more than is really needed late in the season, or it may be too little for good fruit formation if the plant is an apple tree. Another basic guideline is an inch per week for lawns. If you have a beautiful bluegrass lawn, that may be about right. Bluegrass needs to stay evenly moist to do well. But if you have a lower-maintenance lawn with fine fescue and perennial rye, an inch a week will be much more than the lawn needs for health. The clearest answer is not to follow any rule, but follow the plant’s condition.

How Plants Use Water
Plants are made up of at least 65% water so having their water needs met has a huge impact on their health. Plants are constantly taking in and giving off water. Most of the water is absorbed by fine feeder roots and carried throughout the plant. Then most of the water the plant absorbed is given back to the environment through its leaves. To illustrate this point, the DNR Department of Forestry points out that a large shade tree that grows 100 feet tall and lives 60 years will take at least 600,000 gallons of water out of the soil in its lifetime, but it will only absorb about 350 gallons. The process of losing moisture is called transpiration.

Effects of Too Much or Too Little Water 
Wilting and yellowing leaves can mean that a plant needs water or has too much. By the time a plant wilts some damage may already have occurred Plants stop growing when they don't have enough water. Foliage that has just barely wilted will usually make a full recovery once it gets enough water. Foliage that has severely wilted may not recover, it is too stressful for the plant. The outward signs of too much water are wilting and yellowing leaves, especially those in the inner areas of the plant. The symptoms you may not notice are that the plant stops growing and stops absorbing nutrients. If a plant gets too much water for very long, roots will begin to die. When there is a question about whether a plant is wilting because it needs water or because it has too much water, feel the soil and don't be deceived if the surface is dry. On a hot, windy day, the surface will dry out even if the ground is saturated. Poke into the soil several inches, and if the soil is damp, don’t water. The is especially true for container plants outdoors that may be dry on the surface while waterlogged further down.

Judging a Plant's Water Needs
The best way to judge the water needs of a plant is to first learn about the type of plant you are growing. Some are very drought tolerant, others require consistently moist soil. Next, judge the situation where it will be growing. What is the soil type? Sandy soils have very little capacity to hold moisture and dry out quickly between waterings. Soils with lots of organic matter have good moisture retention. Clay soils have good moisture retention but may hold too much water. Is the ground sloped where the plant will be growing? Sloped soil drains much more quickly. You will also need to judge the plant's general condition. A healthy plant with an established root system will be much less demanding than one that is newly planted or one that is already struggling. Taking into account everything you know about the plant you are growing and the site, you can then rely on outward signs. Obviously, if the plant begins to wilt, that is a sign of water stress (too much or too little). The foliage on many plants will start to look "ashy" if they are too dry even before they wilt.

How To Water
Ideally, nature would provide enough slow, evenly spaced rains to meet your plants' water needs. But in reality, you will probably have to supplement nature for part of the season, especially for new plants. How? There are lots of types of watering cans, hoses, nozzles, sprinklers and irrigation systems, each with its own strengths and weaknesses. Pick out a system that works for both you and your plants. As far as your plants are concerned, they need the water applied slowly. For almost all plants, a deep, thorough soaking followed by enough time for the soil to dry out slightly is ideal. Frequent light watering is not good for plants. It encourages shallow root growth. That's why irrigation systems designed for the lawn are seldom adequate for landscape plants and if they aren't set up and operated properly, they can actually be harmful to a lawn too.

Whenever possible, plants should be watered early in the day for several reasons. Plants use the most water during the warmest part of the day. When you water early in the day, you avoid losing as much of the water directly to evaporation. Also, watering early in the day allows the plant foliage time to dry out before evening, minimizing problems with fungal diseases. The amount of water that falls in a given area can be measured by setting out several shallow, straight-sided containers such as tuna or cat food cans.

Conserving Water
Whether there is a water shortage or not, it is always a good idea to take a few steps to conserve or minimize your need for water. In addition to using methods and tools that apply the water exactly where it is needed and in an efficient manner (slowly), you can use an organic mulch. It will help in several ways: Mulching slows down evaporation from the soil surface. It also keeps the surface loose and cool and slows down water loss due to run off. Mulch inhibits weeds that would otherwise take some of the water you are providing your plants. It also encourages good root growth which allows the plants to do a better job at gathering the water they need. Another option is to choose plants that need less water such as native plants. Place plants that need more water together, rather than scattered among the garden.

Additional Bachman's Information
Watering Basics for Indoor Plants
Watering Tips
Understanding Your Soil
Landscape Plants for Special Situations

© Bachman's 2007