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Garden Experiences: Gardening During a Drought

Copyright © 2009-2011 by David E. Ross

Water, water, every where,
And all the boards did shrink;
Water, water, every where,
Nor any drop to drink.

Samuel Taylor Coleridge
The Rime of the Ancient Mariner
(1863 edition)

Background

Southern California (where I live) is naturally semi-desert. We import our water from northern California. A series of northern dams capture snow-melt and slowly release it into the Sacramento and San Joaquin Rivers (and into tributaries of those two), which meet in a delta that empties into San Pablo Bay (a northern extension of San Francisco Bay). Pumps in the delta collect the runoff and divert it into the California Aqueduct, which delivers water to farms and urban areas in the San Joaquin Valley and in southern California.

When this was first written (August 2009), California was in another of its periodic droughts. Of the eight largest reservoirs in the state, one was filled to 80% of capacity (the Don Pedro Reservoir on the Tuolumne River). The other seven were at or below 51% of capacity. The state's entire system of 12 reservoirs were only half full at the beginning of August. Since the springtime melting of mountain snows ended only about two or three months before and would not resume for another seven or eight months, half-full reservoirs were a major concern.

Compounding the drought was the decree of a federal court that limited the operation of the pumps in the delta. The pumps were killing too many small fish that are vital parts of the food chain for the Pacific Ocean fisheries.

The result was a permanent reduction of 15% in water deliveries to southern California water systems (private water companies and government water agencies).

While new gardens should thus be planned and planted for drought tolerance, existing gardens can indeed thrive with less water. This merely requires some gardening practices that should be used even if there were no drought. While the following is oriented towards the soils and climates of southern California, these suggestions can be adapted to other areas.

A river flowed out of Eden to water the garden.

Genesis 2:10

Wise Watering

Even thirsty plants — such as grass lawns and rose bushes — tend to be over-watered. Wise watering involves using the correct amount of water with the correct frequency at the correct time.

The first principle of wise watering is to water deeply and infrequently. This promotes deep roots for most plants. (See mulch regarding plants that are naturally shallow rooted.) Plants with deep roots can survive a temporary moratorium on all watering while plants that are watered daily will suffer or even die if watering stops for even few days in the heat of summer.

However, deep watering does not mean irrigating all in one session. To reduce runoff and make efficient use of water, I water a short period and then stop for 15-20 minutes. Then, I water again for another short period and stop for another 15-20 minutes. Finally, I water a third short period. In the hottest part of summer (95°F or more), I might run my sprinkler system 8 minutes at a time for a total of 24 minutes for each of seven valves; but I do this only once in three days. When the weather is cooler, I reduce the duration of each cycle or even eliminate the third cycle. I use less water than a neighbor who waters her garden daily 10 minutes per valve.

The drip irrigation system for my roses in front delivers water much more slowly than my garden sprinklers. I run the drip system every other day with three cycles of 30 minutes each. My Hill is quite a different situation. I water it every third weekend, running the sprinklers there in the morning on a Saturday and then again on Sunday. In the summer, the sprinklers run 45 minutes for each of four valves on each of those days. This provides deep watering for an area containing drought-tolerant plants; it also allows the surface to dry to a depth of 2-3 inches or more, inhibiting seedling weeds.

Not only do annuals, perennials, and shrubs benefit from deep watering; trees benefit, too. In fact, trees might benefit more than other plants. With deep watering, a tree will have fewer surface roots to break up sidewalks and driveways or to make lawns lumpy, and it will have sufficient deep roots to anchor the tree against a strong wind. Properly watered, some trees will send their roots down 20 feet or more.

But how much water is enough? On the day before watering, dig down about 2 inches. If the soil is slightly damp at 2 inches, you are watering enough. If the soil is quite moist, you are watering too much. Too much water not only promotes shallow roots; it also promotes root-rot and other fungus.

When should you water? A better question is: When should you not water?

• Don't water while rain is falling; you risk over-watering.
• After a rainfall of at least 0.1 inch, don't water within 2-3 days. After a heavier rainfall, wait even longer.
• If the soil surface is wet don't water.
• In southern California, don't water while a strong, dry Santa Ana wind is blowing. Most of the water will evaporate before it hits the ground.
• Don't water so late in the day that foliage remains wet after the sun sets. Depending on the weather and the amount of shade, this might mean not watering after noon. Wet foliage attracts snails and easily becomes infected with fungus. (I water early in the morning, finishing just after the sun rises.)

All day I've faced a barren waste
Without the taste of water, cool water
Old Dan and I with throats burned dry
And souls that cry for water
Cool, clear, water

Keep a-movin, Dan, dontcha listen to him, Dan
He's a devil, not a man
He spreads the burning sand with water
Dan, can ya see that big, green tree?
Where the water's runnin' free
And it's waitin' there for me and you?

Bob Nolan, Cool Water, 1936

Mulch

Watering wisely is not enough. The soil must also be protected from the drying effects of sun and wind. Generally, a mulch should be thick enough to hide completely any bare soil. Mulches can be dead leaves, partially composted vegetation, gravel, small stones, shredded newspapers, plastic sheets, bark chips, nut shells, or wood shavings.

In some of my beds, I use a mulch of leaves from my various trees. This includes the east and circular beds in back. I also use this mulch around my oak (Quercus lobata) in front. Since that location is exposed to winds, I anchor the mulch with poultry wire. Under my guava (Feijoa sellowiana) in back, the mulch is chopped up prunings from that bush. My camellia bed is mulched with the output of my office shredder. I have even used the tiny dead needles from my neighbor's Italian cypress (Cupressus sempervirens) as a mulch for newly planted ground cover.

An alternative to mulch is a dense ground cover. Choose a ground cover that is not thirsty. The west bed in my back yard has cinquefoil (Potentilla neumanniana), and the rose bed has pink clover (Persicaria capitata). Both ground covers are less thirsty than ivy.

Although grass can be considered a ground cover, it tends to be very thirsty. My grass lawn in back — red fescue (Festuca rubra) — is quite small. My "lawn" in front is pink clover with cinquefoil in the parkway.

Besides preventing the loss of moisture from sun and wind, a good mulch will conserve water in other ways:

• A thick mulch inhibits weeds that will steal water from other plants.
• Mulch keeps the soil cool even on the hottest days, eliminating the need to use water for cooling the soil around shallow-rooted plants. (My camellias and azaleas — which are not only shallow-rooted but also require constant soil moisture — get the same once-in-three-days watering as the rest of my garden; their shredded paper mulch provides the right environment without daily watering.)
• Mulch cushions the impact of falling water whether from rain or artificial irrigation. By preventing the soil from becoming compacted, mulch thus preserves tilth and promotes better penetration of water into the soil.
• Mulch also slows the horizontal motion of water, reducing runoff and increasing penetration.
• A readily compostable mulch (e.g., leaves, shredded paper) encourages the activity of earthworms, which improve tilth and thus facilitate deep watering.

A note of warning: With a thick mulch, it is very important to allow the surface of the soil under the mulch to become somewhat dry between watering. Otherwise, surface roots will indeed be at the very surface and even grow up into the mulch. This can defeat the water-conserving purpose of the mulch.

Weeds

Weeds are water thieves! Many weeds have tap roots and consume the results of deep watering. Other weeds — especially grasses — have aggressive surface roots that prevent deep watering.

Do your best to keep weeds out of your garden. Combine both mulching to prevent many weeds and weed-pulling to eliminate those that are not stopped by mulch. Not only is a weed-free garden more efficient in the use of water, but it also looks better. Further, since weeds also steal nutrients and sunlight from other plants, might attract harmful insects, and can be hosts to plant diseases, a well-weeded garden is healthy.

In a dry year, farmers complain of starvation. In wet years, farmers starve.

Folk proverb

Fertilizing

During a drought, be conservative about feeding your garden. Excess nitrogen promotes more foliage, and each extra leaf requires extra water.

Feed your garden in the late winter or early spring, when new growth is just starting. Most plants in the ground will survive quite well without any additional fertilizer later in the year. Grass lawns might not look as nice with only one feeding a year, but they will not require as much water — or as much mowing — as a lawn fed throughout the growing season.

Of course, some plants — such as roses — will not do well without repeated feeding. Containers with a potting mix that drains well will quickly lose nutrients; plants in containers may require frequent feeding.

Tilth

A definition:

tilth

the physical condition of cultivated or tilled soil

Of course, the best time to till your garden is before planting. Once shrubs and trees are established, digging to improve the structure of your soil around and under them becomes impossible. After a garden has been planted, however, it is still possible to improve tilth and thus reduce runoff and increase the penetration of water.

• Two ways in which mulch affects tilth have already been cited. Mulch cushions the impact of water falling onto the soil, thus preventing the deterioration of tilth through compaction. And organic mulch attracts earthworms, whose activities improve tilth.
• Pulling weeds — including their roots — rather than merely cutting them improves tilth by leaving channels by which water can flow below the soil surface.
• Heavy clay soils plague much of southern California. Even after extensive tilling with the addition of organic matter, such soils easily revert back to having very poor tilth. Broadcasting a generous layer of gypsum over the soil at least once a year will improve the tilth of clay soils. The gypsum reacts chemically with the clay to make the latter porous and less sticky, allowing water to penetrate quicker and deeper. The gypsum must be rinsed into the soil, so the best time to apply it is in October, just before the beginning of the rainy season even if the rains are sparse.
• When planting annuals or dividing perennials and bulbs, you have an excellent opportunity to improve the adjacent tilth. Merely dig the planting hole a little deeper and wider than necessary, stir in some compost or peat moss, and then refill the hole to the depth and width actually needed. I also add some more gypsum while doing this.

Pruning

In southern California, most deciduous shrubs and trees are pruned in the winter. Other plants are pruned just after flowering. Very often, this annual pruning can be quite severe; but the plants seem to respond very positively.

However, grooming plants throughout the growing season (e.g., removing dead flowers) is also a form of pruning. Such grooming removes not only dead flowers or other dead growth but also some live foliage.

During a drought, grooming should be more aggressive for many plants. The more leaves removed from a plant, the less water it requires. Even without a drought, I am constantly trimming the growth on my potted dwarf citrus so that the remaining foliage will not place an excessive demand for moisture on constrained roots. When grooming Penstemon, I remove not only the dead flowers but most of the shoot. Not only does this reduce the plant's need for water, but it also causes the plant to grow more sturdy.

All during the growing season, I'm removing stray shoots from many plants. I'm opening the centers of rose bushes to allow better air circulation and prevent mildew. I'm giving the dwarf ivy (Hedera helix 'Hahn's') on my mailbox "hair cuts". I'm cutting the pink clover and cinquefoil away from the walkways in back. While the real purpose of this trimming is to improve the health and appearance of the plants, it also reduces the demand for water.

30 August 2009
Updated 23 July 2011

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