What Are Some Methods Plants Use to Deal With Drying Out?

Short-Term Drought Response

• During periods of drought, plants release a hormone that signals the stomata, tiny pores on the leaves that release water vapor, to close to prevent the loss of moisture. If water is not replaced, the plant wilts and photosynthesis slows and eventually ceases. Plant growth slows down to conserve energy. Herbaceous plants wilt quickly, but woody plants, such as trees and shrubs, usually withstand drought longer by storing energy in their roots and stems.

  Plants use different short-term strategies to conserve moisture. During hot, dry summers, some deciduous trees and shrubs drop their leaves to reduce water usage. The rose bay rhododendron (Rhododendron maximum), which grows in U.S. Department of Agriculture plant hardiness zones 4 through 9, rolls its large leaves into tight cylinders to conserve moisture. Many grasses go into dormancy during dry spells, turning yellow and dry. Dormant grass may appear dead, but quickly revives when rain returns.

Water Storage

• Succulents, such as cactuses, survive arid, desert conditions by storing water in their leaves, stems or roots. A thick, waxy cuticle covers their leaves and stems to prevent water loss. Most succulents have shallow root systems that enable them to absorb rainfall quickly. These plants tend to have few or no leaves and many have spines which help dissipate heat. Succulents reduce water usage by conserving energy. For example, they often perform photosynthesis during cooler nighttime temperatures. Succulents usually have slower metabolisms and consequently slower growth rates.

Root Systems

• Phreatophytes are plants that survive dry conditions by developing deep, extensive root systems. For example, the honey mesquite tree (Prosopis glandulosa), which grows in USDA zones 6b through 9, has two types of roots: wide-spreading surface roots to absorb soil moisture and a tap root long enough to reach the water table. This tap root can grow more than 40 feet long. The creosote bush (Larrea tridentate) uses a combination of a deep tap root, surface roots and small, waxy, bitter-tasting leaves to survive desert conditions. This plant drops its leaves during dry spells and can survive up to two years without rain. Cresote bush grows in arid regions of USDA zones 8 through 10.

Drought Avoidance

• Ephemerals are annual plants that avoid drought by completing their life cycles when moisture and temperature conditions are favorable. These plants germinate, bloom, disperse seeds and die within a short period of time. Many ephemerals live in regions that experience regular seasons of drought and rain. Ephemerals produce extremely hardy seeds that can sometimes lie dormant for years until rain stimulates the seeds to germinate and grow.