FROM THE BORDER / OCTOBER 2009

100 WORDS FOR DROUGHT TOLERANT
by Hilary Gordon
Photos by Blair Randall

As a schoolgirl I learned that Eskimos have 100 different words for snow. That made sense, since snow could be what you build your house out of, or what blinds you in a life- threatening storm, or what the seal you are hunting is surfacing through, or 97 other meanings, each different, each very important.

As a college student in the (then) Ornamental Horticulture Department at SF City College, I only learned one word for drought-tolerant plants in 1984. In plant ID class we had to memorize the names, common and botanical, and the characteristics of plants. Each plant was either drought-tolerant or not drought-tolerant.

Twenty-five years later as water policies and practices have come under more and more pressure from increased demand and shrinking resources, we need one hundred words for drought-tolerance. Part of the task of the Garden for the Environment is to refine what this word can mean, and experiment with real world plants, soil, weather and exposure, to find out which plants can thrive with little or no reliance on summer irrigation. (PHOTO: Zauschneria at the GFE, 2009)

Our first task was to create ‘hydrozones’ in the garden. This meant that instead of watering the entire garden every time we watered, some garden areas, where vegetables, fruit trees, roses, and other tender plants lived would be watered twice a week, while the drought-tolerant demonstration areas would be watered twice a month in dry weather. Some garden areas, where native plants were well established, actually needed no summer water.

The next step was to observe the success of plants in the drought tolerant areas of the garden. It turned out that many of the plants from the original plantings in the 1990’s were not actually capable of performing with really limited irrigation. One important plant in the original drought tolerant areas of the garden is Miscanthus sinensis. This is a large, arching, variegated grass which flowers beautifully at the end of summer with silky, bronze blooms shooting up over the clump of leaves. These blooming grasses were a big part of our loveliest cut flower bouquets the first Fall I worked in the garden. But it turns out that these grasses are not actually able to bloom without regular watering. They grow, but don’t bloom on the twice a month regimen. They may be more drought-tolerant than water-hogs like roses or Japanese maples, but they don’t actually belong in the drought-tolerant garden display. (PHOTO: Miscanthus at the GFE, 2009)

According to the Sunset Western Garden book they need “moderate to regular water.” They do make it into the East Bay MUD book Plants and Landscapes for Summer-dry Climates, which lists only plants appropriate for our Mediterranean climate. This authority says that they need “moderate” water. According to the Dry Gardening Handbook, by Olivier Filippi, “if they are to give generously of their foliage and flowers, they really do need water”, all except one cultivar, Miscanthus sinensis ‘Yaku-jima’.

So which is it? Are they appropriate for a summer-dry climate? Do they need moderate water? Or regular water? What about if they are planted in poor, sandy, soil? They would probably need more. How about right near the ocean? They would probably need less. If planted in a hot location, like the east side of Bernal Heights, would they bloom with only occasional water if given part shade during the middle of the day? (PHOTO: Yarrow at the GFE, 2009)

To completely muddy the waters, Plants and Landscapes for Summer-dry Climates gives the following six warnings to go with their water recommendations for plants in our dry climate. First, plants that prefer seacoast conditions must be planted near the coast. Drought-tolerance on 33rd Avenue in San Francisco or in Walnut Creek would be a completely different story. Second, that the previous winter and spring have provided “normal” amounts of rain. Third that plants are already well established. During their first and sometimes second years in the ground, even very drought-tolerant plants require extra irrigation. Fourth, when irrigation is used, plants are watered deeply. Superficial watering will cause even a drought-tolerant plant to develop a superficial root system which will never stand up to prolonged dry soils. Fifth, soil is well-mulched, and finally that drainage is adequate.

So is my newly-purchased plant drought-tolerant or not? The answer comes in many shades of grey. I can’t yet offer 100 words for drought-tolerant, but here is a beginning.

Summer-Dry Climate: Our normal climate in the Bay Area generally provides no rainfall from June until November. There are many regions of the world with similar climates, known as “Mediterranean” climates. Plants from these regions often do well in the Bay Area.

Drought: A year, or series of years, in which winter rainfall is below normal, resulting in dry soils, small snow packs, and low reservoirs. Little or no water is available for garden irrigation.

Drought-tolerant once established: A phrase traditionally used by gardeners to describe plants that can thrive in dry soils for some period of time. How long? Ask the gardener. Better yet, ask the plant.

Not drought-tolerant: A plant that needs continuously moist soil for good results.

Best with occasional watering: An irrigation regimen that calls for several deep irrigations during our dry summers, such as 3-4 times a year. These plants might become dormant and stop blooming if they do not receive any summer water.

Moderate watering: An irrigation regimen that calls for regular but infrequent deep irrigation during our dry summers, for example, every other week, or 10-12 times a year. These plants might actually wilt and die if they do not receive any summer water.

California native plants: Careful! Some California natives are streamside plants, like willows or big-leaf maples, that actually expect lots of summer water.

Xeriscape or Raingarden plants: Plants that require or prefer no summer water once established. Many, but not all, sun-loving California natives fit this profile.

In the San Francisco Bay Region we don’t really need more than one word for snow. But we could use much more specific language about drought-tolerance. Sometimes a slight shift in language can reflect a sea-change in awareness.

Hilary Gordon is Perennial Plants Collection Manager at the GFE.  A life-long gardener, trained at the City College Horticulture program, she has worked as a professional landscape gardener from 1984 until the present.  

Have a question for Hilary? Meet her in the garden Wednesdays 10-2 and Saturdays 10-4.