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Gardening in the Drought: What Makes a Plant ‘Drought-Tolerant’

| August 15, 2014 | 1 Comment
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By Kathy Shield
Intern, Forum

California’s historic drought has lots of gardeners searching for drought-tolerant plants. But what, exactly, makes a plant drought-tolerant? The term is a “catch-all to describe using plants that use less water,” Flora Grubb, the owner of a San Francisco garden store, explained on Forum.

Falling into that “catch-all” category are plants that have evolved different physiological strategies to survive the dry times in California.

When it comes to drought-tolerant plants for your yard, Sunset’s garden editor Kathleen Brenzel has one recommendation: “The best thing you can do is choose appropriate plants for your region.”

Tiny Hairs

Twinberry honeysuckle has tiny hairs that help it collect water. (docentjoyce/Flickr)

Twinberry honeysuckle has tiny hairs that help it collect water. (docentjoyce/Flickr)

Some drought-tolerant plants use trichomes, or tiny hairs, to grab water and hold onto it. These hairs reduce air flow over the leaves of the plant, reducing evaporation. Plants that are native to foggy coastal regions use trichomes to pull water from the air. Some plants can get half of all their water this way. Trichomes cover the flowers and leaves of Twinberry honeysuckle (Lonicera involucrata), which grows along the coastline from Alaska all the way to Mexico.

Waxy Surfaces

The waxy surface on the agave helps it retain water. (John Loo/Flickr)

The waxy surface on the agave helps it retain water. (John Loo/Flickr)

All plants have a thin waxy cuticle, but many drought-tolerant plants grow thick coatings as a barrier against the environment. Plants in limited water environments develop these coatings to help retain water by limiting transpiration. Agave plants, such as the Southern Californian desert agave (Agave deserti), have thick waxy layers on their leaves, which insulate the plant from the hot desert sun.

Lateral Roots

The California oak's roots extend far and wide. (Josh Mazgelis/Flickr)

The California oak’s roots extend far and wide. (Josh Mazgelis/Flickr)

Plants native to different regions have evolved different root structures. In general, trees grow a single, wide tap root deep into the ground, which gives the tree dependable moisture. In regions with dry summers, trees also grow lateral root systems along the surface, which give the tree stability and the majority of the moisture and the nutrients it needs. The California oak tree (Quercus agrifolia) has a root system that extends as far as 90 feet beyond its branches, adapted to wet winters and long, dry summers throughout the state.

Water Storage

Succulents can store water in their leaves to hold them over during dry periods. (FarOutFlora/Flickr)

Succulents can store water in their leaves to hold them over during dry periods. (FarOutFlora/Flickr)

Succulents are particularly drought-tolerant. They contain tissue capable of storing water, so they can survive for short periods without water. They often have thick, fleshy leaves, like spiral aloe (Aloe polyphylla) a non-native plant that does well in regions with variable water supply, including the Bay Area. Some succulents can also store water in their stems and roots, including certain bulbs.

For tips on creating a drought-friendly garden, listen to the full Forum episode:

 

 

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KQED Science brings you award-winning science and environment coverage from the Bay Area and beyond by the flagship Northern California PBS and NPR affiliate.
  • http://www.PlantRight.org Merry Weather

    Thank you KQED, for inviting these experts to help our community make even better plant decisions in these very dry times for California. In addition to looking for drought tolerant plants (in your region), it is important to choose non-invasive plants. Visit PlantRight.org to make sure your water-wise plant is a truly wise choice.
    Recent examples of invasive plants that have been unfortunately recommended as ‘favorite’ drought tolerant choices for California landscapes include: Mexican feathergrass (Nassella or Stipa tenuissima), and Green Fountain Grass (Pennisetum setaceum). Don’t be fooled by these deceptive beauties.