by Gaston Tessier
Water makes up over 90% of every plant we grow. It keeps leaves and stems turgid and prevents them from collapsing. Wilting is the result of this collapse when the source of water stops. After the hot and dry summers of the last few years, we may have to review our gardening situation and amend our soil to absorb and retain more water. We waste a tremendous amount of this precious and exhaustible resource. A very scary fact is that normal yearly rainfall replaces only 75% of the groundwater reserve that we utilize. Studies estimate that half of this water is wasted. By 'wasted', they mean that it is applied unnecessarily, lost to evaporation or contaminated by runoff.
These facts explain the rise in the cost of water and the watering restrictions imposed on residents in different communities. Using less water is the only solution available to the homeowner determined to control the cost of this essential utility. This does not mean that we have to confine ourselves to planting cactus and yucca. Nor do our yards have to be become concrete, gravel, or plastic sheeting. We just need to be more discriminating about when and how we water and what we plant in our yards.
Water-holding Capacity Test
We should be aware of our garden bed's water-holding capacity. The following easy test is a much better way to figure out when to water than waiting for plants to wilt. It should be done after a few days without any rain.
- First, soak a 12-inch-diameter spot with a hose for about two minutes.
- After the water has had a chance to settle, thrust the head of a trowel into the spot so it reaches 3 to 4 inches below the ground level.
- Pull the trowel toward you to make an opening, and then reach in with your hand to feel the soil at the bottom of the hole. When watered well, the soil should feel cool and damp.
- Dig a new hole in the same spot every day and note the number of days that elapse until the soil at the bottom of the hole feels warm and dry. That is the number of days that you can go without watering during a dry period.
Remember that weather conditions also play a part in determining a watering schedule. Be prepared to adjust your original findings throughout the growing season. Soil that remains moist for five days during the spring and fall may become dry after 3 days during the hot summer months when surrounding shrubs and trees have leafed out and are taking much of the surrounding water.
Type of Soil
Soil type is really what determines water needs. Some soil drains too quickly and others too slowly. In sandy soil, the space between the grains of sand allows water that is not immediately absorbed by the shorter roots of annuals and perennials to go deeper in the soil where it is immediately taken by the roots of shrubs and trees. On the other hand, the tightly packed, fine-textured particles of clay soil, hold moisture so well that the water will displace the air in the root zone and cause roots to rot and plants to die.
The happy balance is loam. A loamy soil holds moisture in the ground and permits just the right amount of air to penetrate and maintain it in a crumbly state. The structure of your soil can be altered to retain just the right amount of moisture by adding peat moss and compost. In most areas, topsoil is only 3 to 5 inches deep. Disturbed areas like those around our houses have even less. Even in well-established gardens, loamy soil should be amended with organic matter annually to keep it healthy and absorbent.
Slope and orientation can also affect a soil's water needs.
You can determine if your soil has a drainage problem by doing the following test. Dig a 12-inch wide by 18-inch deep hole in your garden and fill it to the top with water. Let the hole drain and fill it with water again. If the water drains away within a few hours, your soil is excessively well drained and will require frequent watering. If the water drains out in 12 to 24 hours, your soil is well drained, and you can grow almost anything without a problem. If the hole still has water after 24 hours, your soil is poorly drained. Amend it or grow wetland plants. An alternative would be to build a raised bed over the area. Most plants need an 18-inch depth of well-drained soil to achieve their potential.
Knowing how much water an area can absorb is very important. If the absorption of your soil is poor, whenever we get a downpour of rain, or if you water, most of the water will end up in depressions away from your plants and too often directly into the sewage system. A simple way to test infiltration rate is to water an area and note how long it takes the water to run off onto surrounding areas or begins to puddle in depressions. For a thorough watering, soil should be moistened to a depth of 4 inches. If the run off occurs before reaching that depth, it may be necessary to water in several shorter periods to achieve the desired depth of moisture. Note that clay soil can become so crusty on top that it will not be able to absorb water in its pores as quickly as the rain or hose will provide. Water will at times bead up and simply run off if applied too quickly. I found that by first wetting the surface it opens the way for the rest of the drops to follow. In my case, applying 2- to 3-inches of mulch or organic matter has created a sort of sponge that can quickly absorb and hold moisture to later ration it to the roots as needed.
After these dry summers, I am considering re-grouping moist or dry requirement plants together. For new gardeners, I would recommend planting species in a group according to their water needs.
A form of drip irrigation to get water down to the plant roots and in the right amount is also important. Once installed, a drip irrigation system reduces the time spent watering and the amount of wastedwater nearly to zero. Covered by a light layer of soil or mulch, it reduces the amount of water used by at least a third. At the current price of water, one can recover the cost of drip irrigation material in only a short time. Another great advantage of drip watering is that leaves remain dry because water is applied at or just below the soil surface, eliminating many plant diseases. Weeds do not thrive because there is less water on the soil surface.
Most homeowners water lawns once a day or every second day, wasting a huge amount of water. A thorough watering once every five to six days should be sufficient if your grass is growing on the proper amount of topsoil. Lawns need at least 4 to 6 inches of topsoil to allow grass to grow deep root systems in order to survive during drought periods. Those of us living in new communities have lawns growing on 3 inches or even less. Amending your soil is almost as important as keeping it well watered.
The choice of grass can also determine the amount of water required for a green lawn. Kentucky bluegrass, the favoured lawn grass, produces a beautiful lawn, but it requires almost 40 inches of water each year. Native grasses can thrive in their growing conditions with only the water that naturally falls from the sky. Native plants have that advantage too.
On a personal note, I am eliminating more lawn each year; ince I cannot justify using the amount of water needed to sustain this greenery which, the more I water, the more it grows and therefore has to be continuously mowed.