Plants Stop Growing
Plants have a very simple reaction to too little or too much water--they stop growing. When a plant stops growing, it fails to perform both in the size of its blossoms and in the size of the entire plant or blade of grass. Plants vary in the amounts of water they need. Because their root systems are deep and water-retentive, most trees are usually able to withstand dry periods. Likewise, the many shrubs and perennials in your landscape are better equipped to cope with dry spells (the exceptions being the shallow rooted rhododendron species). The plants to watch are the annuals and the lawn. Because they are shallow-rooted, and because they grow and flower so actively all season long, annuals need a more constant supply of water than do other plants in the landscape. Lawn grasses exposed to full sunlight, if not growing in absolutely perfect soil conditions, also suffer from thirst as the summer weather heats up.
Wilt Is Too Late
The problem is that when a plant starts to wilt from lack of water it has already stopped growing for a day or more. This wilt is different from the temporary wilting that can occur on some plants during the heat of the day in midsummer. This mid-afternoon wilting is not necessarily a sign of serious water trouble. When the sun is most powerful, photosynthesis is at its water-demanding peak and plants droop a bit. Temporary wilting shouldn't be ignored, but it is not automatically a cause for alarm. Wilting that extends beyond the heat of day, especially if it occurs in the morning, is a signal that the plant is suffering a serious water shortage. It is important to water it immediately.
If possible, anticipate a plant's water needs before growth even slows down, much less stops. Try to keep the water supply as consistent as possible.
Keep Track Of Rainfall
Keeping track of rainfall helps you avoid overwatering or underwatering your landscape. Rainfall patterns are the best guide for deciding when the lawn and garden may need supplemental watering. Mount a rain gauge someplace in or around your property, preferably in a place you can see from inside the house so you do not have to get wet to check it on a rainy day. A rain gauge is a plastic calibrated tube. Use it only when the temperature is well above freezing. In early spring and late fall, you must keep a watch out for possible overnight freezes, since this might crack the gauge.
An alternative to a commercial rain gauge is an old coffee can set out to catch the rain. For quick and accurate measurements, mark a plastic straw in inches and fractions. After it rains, insert the straw to the bottom of the can, put your thumb over the top end of the straw, and withdraw it to read the depth of the rainfall. Remember to empty the can after each rainfall.
Keep track of the rainfall on a weekly basis. If, after a few days, you have not gotten 1/2 to 1 inch of rain, you should think about watering those plants most likely to need some moisture, including annuals, new transplants, and perhaps the lawn. You don't have to keep precise records on paper. Just keep rough track in your head.