Features and Occasionals

In the Garden: The Hows and Whys of Water

By Kay Denton

In the arid high desert, planning ahead will help you make the most of your precious water.

Despite the fact that many of us have watched animals stroll two by two toward a large boat in the west desert over the last few months, we actually live in high desert country and are entering a dry spell. July is usually the driest month in Salt Lake City with an average of .72 in. total precipitation for the 31 days. Utah is the second driest state in the nation, bested only by Nevada. Given these facts, it’s increasingly important to become water-wise if you’re not there already.

Here are practical pointers that will help you make the most of your water resources—and, if you really want to know what’s going on out there—a microcosmic peering into the cellular life that’s raging in your very own plot.

What plants do with water

Plants have evolved a slick push-pull system to move water into their cells and around their interior. Osmosis (“a push” from the Greek osmos) is the pro­cess by which water tries to equalize its concentration on both sides of a cell membrane after it crosses into a root’s cells.  They protect themselves through selective permeability that allows the inward, but not outward flow of dissolved substances.

The plant stores water inside little sacs in their cells, where the water expands and presses the cytoplasm (the living substance of a cell excluding the nucleus) against the cell wall. Voila, a turgid plant!

That’s the push, which works well in my penstemon, but not so much in my 60-foot Austrian pine. Getting water that high requires transpirational pull, essentially suction in which one source of internal water replaces another lost to the process of transpiration, vegetation’s form of sweat. We feel transpiration’s positive effects when we appreciate the coolness under a tree on a hot summer day—the result of higher moisture content derived from transpiration. Botany for Gardeners author Bruce Capon says a large maple can transpire 58 gallons per hour. Plants transpire 98% of the water they absorb.

All living beings require some level of moisture, including drought-tolerant plants.  Xeriscaping is about being efficient with a limited resource.

Plants break water down into its component atoms through photosynthesis, which uses energy from the sun plus hydrogen from water mixed with CO2 to create carbohydrates like glucose. Only plants have this ability.

Plants use water as we use blood—as a vital transport method. Water dissolves soil nutrients to enable uptake by the roots. Plants rely on water-based mixtures to move manufactured compounds such as carbohydrates, pigments and hormones from their point of creation to be used or stored.

Turgor is such a sturdy, hefty word. It sounds substantial when you say it (go ahead, say it). It’s the fullness or tension or pressure generated by plants taking up water through their roots and distributing it to the cells and tissues. Low water equals floppy plants.

Water also performs as a passive coolant, especially on hot summer days. As it moves from roots through the vessels and tissues and out the stomata (microscopic pores on the surface of plants) via evaporation, water keeps the plant from frying.

Plants aren’t the only water users in the garden. Microbes that help break down organic matter and free up nutrients are aquatic. They live in water coating the surface of soil particles. Earthworms, millipedes, and beneficial insects living in the garden all need moisture to live.

Ye honorable rainbarrel

I was astounded to realize last year that collecting rain water or snow melt was an illegal usurpation of the state’s water. Fortunately, the Utah Legislature saw the error of this way and passed SB 32 (2010) which allows the collection and use of precipitation from your own property without having to obtain water rights.

Rain barrels are sold commercially, or you can scrounge a 55-gallon drum (not previously used to store oil or hazardous waste) and set it on a sturdy base. (Soda bottling companies here in SLC have a waiting lists for empty 55 gallon syrup bottles. Coca Cola: 801-816-5300, Pepsi: 801-972-2732. Utah Barrel Supply has new 55 gallon drums for $50: 801-363-1933.)

You can channel the rain from your house’s roof using the rain gutters. Place a screen over the top to keep out debris and birds looking for a nice bath, and add a tap at the bottom for a hose connection.

A surprising amount of water, even in arid SLC, can be collected. Our driest month, July, sees an average of 0.77 inches—which works out to be about 480 gallons for a 1000 square foot roof (see www.watercache.com/resources/calculators for a rainwater catchment calculator).

Practical tips

• Different plants need different amounts of water. When planting, think of your yard like a house with rooms catering to various needs. Mine is set up with five- to seven-day watering areas near the house and 10-day tracts further out. The latter outnumber the former. Obviously, a prolonged dry spell would require additional watering.

• Watering in the morning allows the plants to use the water for photosynthesis. Later in the day, water evaporates rather than being absorbed. Evening water sets up conditions that contribute to mold and fungal diseases. So get up and get outdoor early, for the good of your garden.

• Sandy soil drains water quickly, which can mean more frequent waterings are necessary. Clay’s lack of porosity can result in water-logged soil that keeps air needed for photosynthesis from reaching the roots. The solution for both these types of soils is to mix in humus (decomposed organic material) and silt (very fine inorganic components) to create a balanced compound that holds the water and allows air flow.

• When to water depends on the vegetation’s needs, the weather and soil type. Young transplants require more frequent watering. This is especially true for trees, which can take up to a year to establish themselves.

•A simple method for determining if it’s time to water: Stick a large screw driver or a knitting needle into the ground. If it reaches less than six inches, turn on the sprinklers. Most roots grow six to 18 inches deep, and that’s the depth the water needs to reach. This method allows you to make watering decisions based on soil conditions rather than an arbitrary time schedule.

• Garden plants require about an inch of rainfall weekly, the result of evolving in temperate zones. If you use overhead sprinklers, place a shallow container in the middle of the garden area and water the space evenly. When an inch is reached, you have an idea about how long to water each time.

• Another trick is to water a section evenly for five minutes. Dig a small hole 24 hours later to see how deeply the water penetrated and then divide the number of inches into 60 to get the minutes of watering required. Thus, if the moisture has penetrated two inches, 30 minutes of watering is needed each time.

• You can estimate water needs by calculating an approximate amount of evaporation loss. Fill a flat, deep pan with six inches of water and place it where the sun’s rays are the most intense. Measure the level after 24 hours to gain a rough estimate of the potential loss rate.

• Water when the garden seems to need it for the length of time that seems right. This takes some willingness to experiment with your vegetation, but it does enhance your intuitive sense of gardening.

• Mulching is all about the water. Well, mostly. It’s most important during the hot, dry months of July and August. Replenish the areas that are looking a little thin.

• Weeds may be pretty, but they suck up the water at an astounding rate because of their deep roots, depriving the plants you want to cultivate of nutrients and coolant. Pull them up and compost them.

• Choose a watering method that suits your needs: Drip irrigation offers slow and even application of water by using low volume emitters, micro­bubblers, microsprays, or long, flexible plastic tubes, with either an automatic or manual operating system. It lowers evaporation rates, aims the water where it’s needed, and provides a steady amount of water. They require maintainance, however.

• Sprinkler systems with automatic timers ensure that a given amount of water is released in specific areas. The two major disadvantages are damaged sprinkler heads and improper pressurization. Old school sprinklers allow more flexibility in placement, but require the gardener to turn them on and off and to move them from spot to spot manually.

• Hand-watering is garden expert Fred Montague’s choice, which he feels emulates a gentle rain better than anything. He recommends a watering wand or a Haws watering can, which has a long spout for better balance.

Kay Denton writes and gardens in Salt Lake City. She is a longtime Catalyst contributor.

This article was originally published on July 21, 2011.