Gardening In The Idaho Sahara 

The challenge of saving water

You'd think after having lived in and around Boise for the past 20 years that I'd be use to irrigating when summer rolls around, but I'm not. Coming from the Midwest, I've never quite gotten use to the idea of watering outside plants to keep them alive. I lived most of my life where it rained; I mean really rained. When a storm rumbled onto the horizon back in Illinois, it was for sure going to be a drencher complete with a horrendous lightning display, house shaking thunder and maybe a tornado thrown in just for fun. Those were real storms. But in Southwest Idaho, heck, when storm clouds gather on the horizon it usually means one of two things: the dark clouds will blow over without a trace of rain or it'll lightning and rain briefly, just enough to settle the dust and start a few range fires, but nothing measurable out in the garden.

Because of the lack of help from Mother Nature out here, the biggest problem gardeners face is knowing how much to water and understanding how to conserve that moisture. Let's start with conserving moisture. Mulching may well be the most important thing that you can do for your garden or landscape when it comes to saving water. A mulch is any material laid over the soil surface to protect it. Mulches do many wondrous things. They provide protection against erosion and compaction, they reduce weeds and moderate soil temperatures, they conserve moisture, and they add nutrients and organic matter to soils (if they happen to be an organic mulch).

The soil under a thick layer of mulch stays cool and moist in the summer so roots are protected from temperature extremes and dry conditions of bare soil. Naked soil isn't natural. Just look at any hillside that has slumped or broken away to expose bare dirt, eventually plants fill the area to cover it. That's Nature's way. Only we silly humans try to keep soil bare around plants exposing the soil and those tender plant roots to the harshest of conditions.

The added bonus of eliminating many hours of weeding is reason enough, in my book, to use mulches. To be effective against weeds, mulches must be deep—about 3 to 4 inches deep. Straw or hay used as mulch in the veggie garden would be exceptions, because of their loose, lofting quality you'd need a layer 7 to 8 inches deep. Chopping the straw or hay would make it a denser, tighter cover.

Mulch cushions footfalls to reduce compaction in a garden or landscape and it keeps mud off your shoes. If there's fruit growing close to the ground like strawberries, the mulch will keep soil from splashing up on the berries during watering, and it'll reduce soil-borne diseases on all produce by keeping it up off the ground.

Mulch doesn't reduce soil compaction if you're using stone as your covering. Stone will compact the soil and make an area hot due to the heat it holds and radiates back. The benefit of using gravel or cinders though, is that they don't have to be reapplied or 'touched up' periodically like wood mulch.

The black, woven plastic fabrics that are commonly used today in landscapes are a vast improvement over the solid sheet plastics used in the 1960s and 70s. That awful stuff restricted water and air movement into and out of the soil, and was death on more landscape plants than anyone will ever know. The new woven, weed barrier cloths allow air and water to move into and out of the soil freely, but they can be expensive and they aren't easy to work with, nor are they always weed-proof. Some landscape maintenance crews have told me that grasses can sometimes come right through the weave and make a real clean up nightmare. Because these weed cloths are made of plastic, they will breakdown in ultraviolet light and will need to be protected with another mulch. Consequently, you end up paying for two mulches instead of one.

Just about any material can be used as mulch. Dry grass clippings, shredded leaves, pine needles, straw, compost and mint sludge (the left over mint plants after the distilling process) all work as garden mulches, but in landscapes, wood and stone products are preferred. Even odd things like old carpet, cardboard and newspaper will reduce weeds and conserve moisture. The newspaper, used shredded or in sheets, would need to be topped with another type of mulch to keep it in place and you'd only want to use the black and white pages. Colored inks contain heavy metals, something that you don't want in your garden. The oddest thing I ever saw used as mulch was sheep fleece; like a wool blanket it could be used over and over again for years.

The only drawback to mulching is getting enough of the stuff laid down before the hot weather and weeds start. Keep mulches an inch away from plant stems, especially trees and shrubs. A damp mulch up against a stem can cause the stem to rot.

Now back to the watering question. Keeping water close to the ground by using drip irrigation or soaker hoses will reduce much of the evaporation that occurs when water is flung into the air. If modifying an existing sprinkler system isn't an option, than water early in the morning or late at night to avoid losing moisture to evaporation during the heat of the day.

It isn't hard to determine how much water plants need—one to two inches of water (over the entire root system) per week usually works with most plants from grasses to trees, with the higher amount given in the hottest part of the summer. The key to that rule of thumb is knowing how deep and extensive the roots systems are on your plants. Empty soup cans laid out over a sprinkler pattern will help determine how much water your sprinklers are putting out at one time. Take the average of the cans.

How long it takes your soil to moisten down to a depth of 12-inches where the majority of roots are found is another head scratcher. Sandy soils, like those found around Eagle and in the foothills wet up quickly and dry out fast. They'll need to be watered every 2 or 3 days, but it won't take long for water to get down a foot. Trying to get water to penetrate clayey soils is another matter.

It takes a long time for water to infiltrate clay down to the one-foot mark. The idea with clay is to water longer than with sandy soils, but infrequently. Check moisture depth using a shovel or soil probe (a hollow metal tube used to take soil cores). If the soil is not moistened down to 12 inches (it should feel like a rung out sponge there), then turn your sprinklers back on. Clay soils hold water for a long time, even up to a week, so you won't have to water but once or twice a week if you're watering deeply.

It takes awhile to learn how your soil and irrigation system work together to determine just how long to water in your yard. And there are variables, for instance, the north and east sides of a house are more shaded and won't need as much water as the hotter south and west sides of a house. Areas under trees or shaded by a fence won't dry out as quickly as areas in full sun. Places that have had the soil amended will infiltrate water faster than areas that haven't been prepared. Slopes allow water to run off and barrier layers underground like hardpan (caliche) or bedrock interfere with drainage and root development.

A few clues that you aren't watering correctly are: water running down the curb, your shoes making sucking sounds as you cross the turf the next day after an irrigation, any need for hip waders in the yard (flood irrigators you're exempt), or a soil so hard, dusty and dry that you bend shovels and your neighbors call your place "Little Sahara."

That plants grow as well as they do in this "must water" region amazes me. It reminds me of the woman who had just moved into the Treasure Valley and asked me what kind of plants would grow in her yard that didn't take "any water or care." When I pointed at the foothills and said, "What you see out there," she gave me the strangest look. I expect she was from Illinois.

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