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Which plants can survive drought? And how much to water the others?

Which plants can survive drought? And how much to water the others? This summer, gardeners in water-short communities of northern California are again faced with questions that last surfaced during the drought of 1976-77. How do you irrigate valuable, established landscape plants when water is scarce?

Which plants should get first claim on available water, and which can survive (or even thrive) on less than you normally give them?

We asded horticulturists to identify which of northern California's most widely grown landscape plants (ones usually watered) would most likely make it through summer without any water, and which would need irrigation. What follows represents their best estimates, based partly on lessons learned during the last drought.

Be warned that these estimates could be faulty. Some plants for which we suggest withholding water might, in fact, succumb; we can offer only an informed hunch, not a guarantee. Learn the symptoms of drought stress so you can recognize plants that might be in trouble: look for wilting or dull-looking foliage or leaves that have picked up a grayish cast.

Specific conditions in your garden can make your plants respond in ways that differ from our guidelines. Young plants, for example, are more susceptible to drought than established ones. Plants growing in shallow soil or exposed to strong winds or bright sunlight need extra water. The same is true for plants that have to compete for water with the roots of other plants, such as large trees, or plants that are used to a lot of water because they grow close to a lawn.

We've left out many herbaceous ground covers that are inexpensive to replace should they fail to make it through a dry summer.

For information on plants growing in your garden but not listed on these pages, see the Sunset Western Garden Book.

These plants will need some water

Japanese maple (Acer palmatum). The large unnamed seedling types should be able to get along quite well with no summer water. However, the smaller grafted varieties (usually the ones with the finely cut foliage) are susceptible to drought. They may need monthly waterings.

Azalea, evergreen. Established landscape plants are surprisingly tough, but they're more sensitive to drought than rhododendrons. Use a wetting agent to aid water penetration. If new foliage droops, the plants need water fast.

Birch (Betula). Many could be in serious trouble without at least one deep watering. Drought-stressed trees are also more susceptible to borer infestation.

Camellias. Large, established plants are surprisingly drought tolerant, but younger ones will need some water. Use an organic mulch around plants and watch closely for wilting new growth.

False cypress (Chamaecyparis). Fancy dwarf types, like the one in the picture at right, need consistent moisture.

Citrus. Response will vary depending on kind of citrus, soil type, exposure, local climate, and even the type of rootstock the variety is grafted to. Watch for wilting, discoloration, leaf drop, and foliage sprouting from the rootstock--in that order--as signs of trouble. You can also reduce water needs by cutting back foliage by up to a third (to prevent sunburn, paint exposed branches with exterior white latex paint). If pruning induces new growth, cut it back.

Daphne odora. Typically, this suffers more from too much than too little water. Small plants will probably need monthly irrigation; larger ones need less or noe.

Fatsia japonica. Plants in shade shouldn't need water, but those in sun might. Look for wilting for new growth.

Ferns. Most low-growing type respond to drought by browning, the going dormant. They come back with winter rains or watering. Mulch for added protection.

Tree ferns need more help. As the ultimate, back-to-the-wall measure, try watering with just 2 quarts of water per plant, poured directly onto the crown. (Water runs down the sides of the trunk and gets into the plant's system because the trunk is an aerial root.) When you have water available, wet the ground as far out as the tips of the fronds.

Fuchsia. In mild climates, older plants with woody trunks may go all summer without wilting. Even if established woody trunked fuchsias lose their leaves and go dormant, they often come back. Young fuchsias with succulent stems will need water, especially if grown in hanging baskets.

Gardenia. If you're lucky enough to have an established, big-flowered type, such as 'Mystery' (fairly hard to grow in northern California), you'll need to water it regularly to keep it alive. Fertilize only if you can water as usual.

Hebe. Small-leafed types take drought better than larged-leafed ones, but both may wilt without occasional watering.

Hydrangea. Can get by with surprisingly little water. Leaves may wilt and drop, but stems should stay green and recover when rains return. If some of the stems dry and shrivel, the plant needs water.

English holly (Ilex aquifolium). Probably the most sensitive of the hollies, it will need monthly waterings and a mulch around its roots. Other hollies should survive with little or no water this summer.

Tulip tree (Liriodendron tulipifera). These suffered during the last drought (their roots are big, succulent, and thirsty). Try to provide one or two deep waterings between now and fall.

Magnolia. Most have surprisingly shallow roots. Large specimens will probably survive the summer without irrigation, but smaller ones may need a monthly soaking.

Passion vine. This will probably need water once a month. If vine covers a large area, cut it back to reduce leaf area.

Podocarpus. Carefully observe plants growing in full sun. A drought-stressed podocarpus first loses leaves, then twiglets, and finally branches. Try not watering until you see stress, then water just enough to prevent worsening.

Rhododendrons. They seem to handle drought better than evergreen azaleas, but they can't be called tough or drought tolerant. When rhododendrons need water, the leaves hang and new growth wilts. Foliage will perk up if you give roots adequate water soon enough.

In hotter sections of northern California, expect some sun scald on drought-suffering plants and, if the salt content in the water rises, burned leaf edges.

Roses. Old (and often irreplaceable) plants can probably pull through a summer without watering. Younger ones will need irrigation. Less water will mean fewer blooms. Don't be in a hurry to remove seed heads. Leaving them on could slow growth--an advantage this year. Remove suckers, but don't otherwise prune until next winter.

Big tree (Sequoiadendron giganteum). This generally needs less water than coast redwood, but trees with twig dieback (common in the Bay Area) could be in serious trouble without deep watering.

Coast redwood (Sequoia sempervirens). In the fog belt, there's no reason to worry. Inland, trees less than five years old could suffer in heat, particularly ones that stand alone. Even light waterings could help these shallow-rooted trees. If suckers form, cut them off.

Star jasmine (Trachelospermum jasminoides). As a ground cover, this is inexpensive to replace if it doesn't survive. If you have a large vine or espalier, prune to reduce leaf surface; water when you can. When stressed, star jasmine begins to drop foliage and turn red.

Viburnum. Deciduous types can take drought, but many of the evergreen ones can't. You may have to water them at least twice this summer.
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Title Annotation:includes related article
Date:Jul 1, 1988
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