Some Approaches to Water Conservation in the Garden

Water conscious gardening is more than just re-using domestic wash-water. The author, an enthusiastic gardener, suggests many ways of looking at water economy.

In a geography class nearly thirty years ago, one of the facts stressed by the professor was that water would be one of the first natural resources to be depleted if action were not taken to insure a conservative use of it. Though difficult to believe at that time, much of California and parts of some of the other western states are in just such a predicament. As a result of critical water shortages, reductions in water use of up to 25% are suggested for residences in many of the coastal areas. Although this sounds reasonable, the actual amount in some areas is based on the number of members in a family and not on a percentage of water used in the past. Thus those who have large gardens or who garden intensively find they have reductions far more than 25%. At our house, we will have to reduce consumption about 80%. This means that we, along with many others will have to conserve water in every way possible in order to keep gardens at a minimum maintenance level. A number of approaches to water conservation are available. Many of them are applicable to saving water in the garden and some of them will be discussed here.

Methods of watering. Of the various methods used in applying water, some use far less water than others. In brief, ditch irrigation uses the most water and should be avoided. Overhead sprinklers use less but may water areas where no plants are growing. Hand watering is probably the best, for the water can be put where it is needed. Also there is less tendency to overwater using this system as contrasted with systems where water is turned on and the device left to be re-positioned at some later time. Soaker hoses also can be used, particularly where plants are relatively close together. When used, they should be placed upside down so the water is not sprayed into the air, allowing for evaporation. Drip irrigation systems are excellent for conserving water and can also be used to water individual plants. Time, effort and expense need to be considered but once in operation it is an easy way to irrigate. Although drip irrigation is most effective in sandy soils, it will conserve water even in the heavier day soils.

Type of plants being grown. There are many lists of plants that can survive low levels of moisture, so most of these plants will not be included here. In general, the larger the plant, the larger the root system to explore for water and the less water it will have to be given. Certain plants such as California natives, most prostrate junipers and many plants native to South Africa and Australia do not need summer water. In the absence of winter rainfall, these plants should be watered in the winter when there is less demand for garden water. Shrubs with deeper root systems will need less water than those with surface root systems, such as rhododendrons, azaleas and camellias. Perennials which can tolerate low moisture levels include columbine, hollyhock, geranium and other Pelargonium species; Liatris spp., Rudbeckia spp., candytuft, Lychnis spp., perennial poppies, some species of Echium, forget-me-not, coral bells, and plants from bulbs, corms or rhizomes such as freesia, daffodil, narcissus, tigridia, gladiolus, agapanthus, watsonia, oxalis, amaryllis, cyclamen, iris, Scilla spp. and sparaxis. Ground covers such as ivy, ajuga, periwinkle, St. John’s wort, Duchesnea indica, Ceratostigma plumbaginoides and ice plant can get by on small amounts of moisture. Some annuals which tolerate low moisture levels include sweet alyssum, marigolds, ageratum, petunias, annual poppies, nasturtium, annual candytuft, mignonette, fibrous begonias, calendula, valerian, portulaca, coreopsis and gloriosa daisies. From your own experience, you probably can add many to this list.

Weeding and pruning. Plants are inefficient users of water and during daylight hours are constantly transpiring water through their leaves. Removal of weeds or any unwanted plants is extremely important. If time is too limited to pull the weeds, a hula or other type of scuffle hoe is suggested. These hoes have a long handle, on the end of which is a knife-like blade which can be pulled just beneath the surface of the soil to cut the roots and thus kill the plants.

Pruning small trees, shrubs and groundcovers also will help. This is a good chance to prune overgrown or poorly-shaped plants. With some plants, it is important not to cut back too far or branches or whole plants may die. For example, when pruning bush daisies or fuchsias, do not prune beyond the last active bud. Once cuts have been made, new buds may be forced and additional pruning then can be done. Many plants can be cut back severely with little damage.

Removal of plants used as ground covers around other plants may be of help. For example, ivy, babies tears or other ground covers sometimes are grown under shrubs such as rhododendrons, camellias, hydrangeas, etc. Such ground covers should be removed as far as the drip line of the shrubs so that water added for them will not be used by the ground covers.

The use of organic material. Organic material in the soil performs many functions, one of which is to retain soil moisture. Organic materials such as leaf mold, decomposed manures or compost can be worked into the soil. In addition, organic materials can be put on top of the soil as a mulch to prevent evaporation. Of the organic materials, compost may be the most readily available, for with the new, rapid, composting method, a new batch of compost can be ready for use every three weeks. There should be no excuses for a lack of abundant compost to add to soils and to be used as a mulch around all plants.

Other cultural practices. There are a number of cultural practices that will help conserve water in addition to those already mentioned. These include such things as scooping the soil away from the bases of plants to make basins that will concentrate the water in the root zones. We have done this to all our rose plants and have filled the basins with compost to prevent evaporation. Plants that tend to be surface feeders can not be treated this way, though a ditch can be made at the margin of the root system that will prevent run-off. On sloping land, soil, rock, brick or wood dams or barriers can be put in to prevent run-off.

Another practice is to lower soil levels of beds so they are not above sidewalks or driveways. This may not always be feasible but if not, the soil should be removed along the edge so that any water running off the bed will collect in the ditch which is formed.

When planting vegetable gardens, make ditches for the rows and then plant into these ditches. This will not only concentrate the water in the root zone and prevent evaporation loss but plants will be less exposed and will lose less water through transpiration.

If winds are a problem, plant rows of vegetables at right angles to, rather than parallel with, the wind. The erection of small windbreaks, even of cardboard will help prevent some water loss through transpiration.

The use of rocks or boards as stepping places in the garden will also prevent evaporation from the soil which is covered. Layers of polyethylene plastic will do the same, but eventually it breaks down in the sunlight and must be disposed of. Compost is better as a mulch.

Concrete retaining walls frequently will draw moisture from the soil. This can be prevented by removing the soil from the wall and painting it with tar or asphalt emulsion. This however, raises the question of whether it is advisable to use one diminishing natural resource in order to conserve another.

Avoid growing plants in containers, for it takes more water to support plants with a confined root system than plants which can explore open ground. Some containers, in addition, are porous and there is evaporation from their surface. If plants must be grown in containers, change to plastic or glazed containers for they allow little evaporation. At the same time, remember that because such containers allow little air exchange, they need to be watched more carefully for they are more subject to excessive moisture and thus root rots may be more common.

Other cultural practices might include watering at night to prevent evaporation, mowing your lawn more frequently to prevent transpiration, and avoiding soil spading prior to planting because this not only destroys soil structure but allows excessive evaporation of soil moisture. Deep spading each year is helpful in removing the roots of large trees near beds because roots tend to accumulate where water is available. Control slugs and snails, for extra water will be required to replace the growth damaged by such pests.

The use of gray water. Gray water, that is, water from the washing machine, dishwasher, shower, bath tub, lavatories or kitchen sink should be saved and used wherever possible. Some cities may forbid this and local regulations should be observed. The main problem from using such water is that detergents are sodium salts of various organic acids and soaps are sodium or sometimes potassium salts of certain fatty acids. Sodium is not used by plants and when it accumulates in soils, may reach levels where it is toxic to plants. Potassium also may reach toxic levels though it is used by plants and also plants are slightly more tolerant of potassium than of sodium in the soil. The use of gray water will depend on how much it is mixed with water not containing these materials. It will also depend on what plants receive it. Acid-loving plants should not receive such water. Members of the monocots and particularly many of the grasses seem quite tolerant of sodium. As an experiment, we are using only the first water from the washing machine to water our lawn. At such time as injury appears, gypsum will be added at the rate of 1 pound per 25 sq. ft. Gypsum contains calcium and it is more active than sodium so will replace it in the exchange reactions in the soil, thus releasing the sodium, allowing it to be leached. Fortunately, soils in this area tend to be high in calcium already and it may not be necessary to add gypsum.

If planning to use gray water, do not use detergents or soaps that have boron, for this material is very toxic to plants. If bleaches or materials containing bleaches are used, allow the water to stand in the open air one day before using it for irrigation. Bleaches are quite toxic but break down in the presence of light and air to form less toxic salts.

Problems that may arise. The main problems from lack of water are obvious. Other problems may also occur. The use of gray water or the lack of enough water to leach the soils may result in the accumulation of excessive salts in the soil and this may result in excessive salts in the plants. Salt damage usually appears as a killing and browning of the tissues around the margins of the older leaves of plants. Plants vary in their sensitivity to this. Salt damage is more likely to occur in container-grown plants than in those grown in open ground. Therefore, when using gray water, do not use it on plants in containers.

Another problem that will occur as a result of low moisture levels will be sun burn. Some plants such as ivy, camellias, rhododendrons, hydrangeas, and fuchsias are more susceptible to sun burn than others. Sun burn appears as a bleaching of the interveinal tissues followed by the death of these tissues. They may remain bleached or sometimes will turn dark depending either upon the plant involved or the colonization of such tissues by fungi which invade only dead tissues.

Wilting may occur but is serious only if the leaves go beyond the permanent wilting point. Sometimes only parts of leaves go beyond this point before water is applied.

When this occurs, the margins of the leaves on the older portions of the affected plants die. They do not turn brown as in salt injury but retain a dull green color and have a crisp, papery appearance.

Benefits. Although it is sometimes difficult to find good in such a serious situation, some good will come of it. Some plants will have to go without water. ‘Such plants as California natives, most of the prostrate junipers as well as some of the plants from Australia and South Africa will thrive far better than when they received too much tender, loving care. Already, one of the live oaks on the campus of the University of California, Berkeley which was on its way out because of summer water, has started to show signs of recovery. One of the more important diseases in California is root rot of the prostrate junipers and particularly of the tams (Juniperus sabina ‘Tamariscifolia’). It will be severely reduced as a result of the lack of water. This may even allow some plant pathologists to work on some new disease problems, maybe even some new ones which will result from the lack of water.