Master Gardeners: It’s HOT Out There… Water Wisely

Water Wisely

One of the most common mistakes made by gardeners is incorrect watering, and in our area, that is under watering. Many people assume flowerthat we are in a rainy climate and watering is unnecessary, or that a light sprinkling will do in dry times. Both of these notions are dead wrong. During the dry periods common to Seattle summers, plants need water, and watering must be done thoroughly. A light sprinkling does not help. Plants absorb water through their roots, so enough water must be applied to soak the soil to several inches deep where the roots are.

Most plant growth, flowering, and fruit production takes place from May to September. Although we get plenty of rain during the winter, these months are quite dry in our region. Vegetable gardens, lawns, and most flowerbeds need about an inch of water each week during the growing season. If rainfall is deficient, these 4 inches a month must be applied through irrigation. Usually, established trees, shrubs and groundcover can get by with far less water.

The only way to figure out when and how much to water is to dig into the soil and see/feel where the moisture level is. Based on this test, you can determine when water is needed and how much to apply. Soil should never be wet on the surface and dry an inch or two down.

Some Watering Tips

  • Use a set sprinkler, not a hand-held spray. Deep watering of even a small garden takes far too long to do properly with a hand-held spray.
  • To save water from evaporating, water during the cool parts of the day. Try not to water during windy times.
  • To help prevent disease, water in the morning or early enough in the evening so that the foliage can dry before nightfall. Always water tomatoes, peppers, and squash at the base, not with overhead sprinklers.
  • Avoid over watering, which may leach nutrients from the root zone.
  • Remove weeds that take needed water from your vegetables and ornamentals.


Mulching weed control and watering are two of your biggest jobs once your garden is planted. Both of these jobs can be easier if you use mulch. The two most common kinds of mulch are plastics and organic material such as straw, leaves, wood chips, clippings, or compost.

Landscape fabric and black plastic are sometimes used as mulch, and under bark or gravel they work well to hold down weeds. So does cardboard or a thick layer of newspaper. For heat-loving crops in the vegetable garden, black plastic provides very good weed control, helps keep moisture in the soil, and allows the soil to warm more quickly in the spring. Poke holes in the plastic so you can water through them. The top of a bed under plastic should be slightly concave to direct water to the plants. A convex raised bed will shed water wastefully onto the paths.

Organic mulches keep the soil moist and help prevent weeds, but they keep the sun from warming the soil. For this reason, it is best not to put organic mulches on vegetable beds until late June in the Puget Sound area. In the rest of the garden, you can apply or renew organic mulches whenever it is convenient. A nice thing about organic mulches is that you can spade them under in the fall or winter, which helps improve your garden soil.

Four Cautions

  • Don’t use grass clippings from lawns that have been recently treated with an herbicide such as “Weed and Feed.”
  • Mixing in large amounts of sawdust or straw may “tie up” the nitrogen in your soil, causing your vegetables to become yellow or stunted. Adding nitrogen fertilizer when you dig in the mulch or plant the next crop will prevent this.
  • Loose organic mulch may provide nice, moist hiding places for slugs, so be prepared to bait for them.
  • Some kinds of organic mulches, especially hay, may contain lots of weed seeds and make more work than they save. Check hay or straw for seed heads before using them as mulch.

[Column courtesy of the Snoqualmie Valley Master Gardeners. More info is available on the SV Master Gardeners website.]

Comments are closed.

Living Snoqualmie