The Mountain Gardener: How to water plants correctly
by Jan Nelson
Jul 18, 2013 | 2171 views | 0 0 comments | 21 21 recommendations | email to a friend | print
A drought tolerant native shrub, Philadelphus lewisii, is also called Wild Mock Orange. It's growing near the Felton Covered Bridge. Courtesy photo
A drought tolerant native shrub, Philadelphus lewisii, is also called Wild Mock Orange. It's growing near the Felton Covered Bridge. Courtesy photo
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The recent heat wave was one for the record books. The temps were not the highest we've ever had around here, but as each day melted into the next I kept thinking that fog, nature's air conditioning, was surely on its way. Even drought tolerant plants need a little help at these times.

Watering is crucial as plants are growing vigorously. Water makes up 90 to 98 percent of every plant we grow. It's needed for photosynthesis, as well as reproduction and defense against pests. Checking soil moisture and improving a soils ability to absorb and hold water should be a priority when you're out in the garden. Don't wait for plants to wilt and burn before correcting watering problems. 

There are ways to water more efficiently and ways to conserve that water. Now is a good time to review some good watering practices and guidelines.

 

When is the best time to water?

Watering in the morning is the most efficient whether you water by sprinkler, drip system, soaker hose or by hand. The water soaks deep in the soil without risk of evaporation. It bolsters the plant for the day and has dried from leaves by evening reducing the risk for foliar diseases like mildew. Plant roots are also more receptive to watering in the morning.

 

Is it true that water droplets will scorch leaves in the sun?

According to a study published in New Phytologist, a journal of research in plant science, there is a slight risk of leaf burn on fuzzy leaved plants in the sun. The hairs can hold the water droplets above the leaf surface and act as a magnifying glass to the light beaming through them. The study also reported that water droplets on smooth leaves, such as maples, cannot cause leaf burn, regardless of the time of day.

I my forty years of gardening, my own observation is that the leaf burn on a fuzzy leaf must be very small, indeed, as I've never observed any damage. If you find a plant needs water midday, by all means go ahead and water it. Containers even benefit from the cooling effect that watering provides.

 

How much should I water?

Most plants need 18-inch depth of well-drained soil to thrive, although trees and many vegetables roots grow several feet deep. More than an inch of water per week may be needed for their success and in the case of many trees and native plants, deeper but more infrequent watering is required.

You can easily measure how much water you are applying. If you have a sprinkler system, place a straight-sided container like a tuna can on the outside edge of the area being watered. Let the sprinkler run until one inch of water has accumulated in the can. When using a drip system or soaker hose, irrigate until a 3-inch deep test hole dug 1-foot out from the emitter or end of the soaker is moist. Moisture at that level indicates that an inch of water has been applied. The best way to determine how many inches of water your soil needs for a good soak is by digging down after the water has had a chance to settle. When watered well, the soil should feel cool and damp at the bottom of the hole. If the soil feels warm and dry you haven't watered long enough. You need to do this test just once to get a feeling for how much water your soil can hold and how deeply it's soaking in.

If you have a lawn, decide if you really need it that large and maybe not in the front yard at all.  Keep the mowing height high during the heat of summer. Mow when the grass is about a third taller than recommended height. For common fescue, mow when the grass is 3 to 4 inches tall, with your mower set at 2 to 3 inches. Fertilize only when your lawn needs it to keep a good green color. Over-fertilizing results in quick top growth which needs more water and is susceptible to insect damage and fungus problems. A good rule of thumb for watering a lawn is to water 1 time per week when the temperature is 70 to 80 degrees, twice per week when it's 80 to 90 and three times per week only when it's above 90 degrees on a daily basis  Make sure the water soaks in which encourages the roots to extend  30 inches below the surface, making your lawn more drought tolerant.

Consider replacing your lawn with a walk-on ground cover like woolly thyme or chamomile.  You can't play touch football on these ground covers, but they will tolerate light foot traffic.  Another alternative is to plant low-growing native grasses that require only a hand-full of trims per year compared to a conventional lawn.

 

Smart watering

Water wisely in other areas of your garden. Construct soil basins and furrows to direct water to plant roots and increase this basin as the plant grows. Another option is to use a soaker hose on the surface to slowly water at the drip line of trees and shrubs. Fruit trees, citrus and flowering trees need a deep irrigation every other week. Less thirsty trees like Chinese pistache and strawberry tree need irrigation about once a month once they are established. Newly-planted trees need water regularly. Gradually reduce the frequency after a year or so.

And above all, mulch, mulch, mulch. Cover the soil with at least 2-incehs of organic mulch such as compost or chipped bark.  The mulch holds in moisture as well as keeping roots cool and gradually decomposes and enriches your soil. Keep it away from the base of trunks or plant stems. Don't use rocks or gravel as a mulch because they add heat to the soil and moisture evaporates faster.

Take good care of your plants this summer.

- Jan Nelson, a landscape designer and California certified nursery professional, will answer questions about gardening in the Santa Cruz Mountains. E-mail her at janis001@aol.com, or visit www.jannelsonlandscapedesign.com to view past columns and pictures.

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