Posted on by tonytomeo

Real Drought Tolerance

Even native manzanitas, which really are drought tolerant, need water until they disperse their roots.

Nearly every landscaper and gardener brags about using plants that do not need much water. Buzz words like ‘drought tolerant’, ‘native’, ‘sustainable’ and ‘xeriscape’ have become all too common, even though few actually spell ‘xeriscape’ properly. (It is NOT ‘zeroscape’!) Unfortunately though, most gardeners water so frequently and generously that drought tolerant and native plants are less sustainable than plants that want more water.

The difficulty is that drought tolerant plants generally need rather regular watering immediately after planting, while they are still dispersing their roots, but then want to dry out between watering once they are established. Otherwise, they are very susceptible to rot if the soil is constantly moist. Most drought tolerant plants should therefore not be mixed with plants or lawns that want regular watering.

Trees like incense cedar, beefwood, carob, silk oak, olive, California pepper tree and some eucalyptus, pine and oak can be nice shade trees in lawns that are not watered too much, but do not live as long as they would with less water. (Although many are messy in lawns anyway; and carob smells bad when it blooms.) California laurel, African sumac, Australian willow, strawberry tree and most acacia and cypress are less tolerant of lawn irrigation.

Eucalyptus, pine, oak and acacia have sensitive roots, so do better if planted while young instead of as larger specimens. For example, #5 (5 gallon) red ironbark eucalyptus get established faster and grow larger than 24” boxed red ironbark eucalyptus installed at the same time.

Bottlebrush, oleander, cotoneaster, hop bush, firethorn, grevillea, some types of wild lilac and all sorts of juniper can be happy with or without regular watering. Manzanita, coyote brush, rockrose, flannel bush and western redbud really want to dry out between watering. Like many plants from arid climates, wild lilac, coyote brush, rockrose, flannel bush and western redbud are naturally relatively short lived. Western redbud fortunately has an efficient technique of producing an abundance of seed and replacing itself with new seedlings before if finishes.

Lily-of-the-Nile is one of the most useful perennials, and can survive with annual rainfall or nearly saturated conditions. New Zealand flax is nearly as adaptable, but is more susceptible to rot if watered too much. Rosemary and several iceplants are nice ground covers with or without regular watering.

The various yuccas, aloes, agaves and their other relatives are some of the most practical perennials for arid climates, and many tolerate somewhat generous watering if necessary. However, most agaves and yuccas have nasty sharp leaves; and some agaves get too big to keep at a safe distance. Also, their bold personalities are not adaptable to every garden style.

Posted on by tonytomeo

Drought Tolerance Necessitates Root Dispersion

Extensive root dispersion enhances drought tolerance.

Fads certainly complicate gardening. Most are merely marketing tactics. Most are bogus. Many even contradict their justifications! For example, most new, trendy and supposedly sustainable plant cultivars are genetically weak because of extensive breeding. Drought tolerance likewise has potential to be a constructive fad, but is so commonly misapplied.

Incidentally, its terminology is somewhat inaccurate. Drought is an extended but unusual pattern of dry weather. Whether the duration is for one year, or many, it is not permanent. The dry weather that persists through summer locally is normal for the chaparral climate. It is therefore a normal characteristic of climate, rather than abnormal weather conditions.

Drought tolerance is therefore practical here as chaparral tolerance. Most plants that are drought tolerant are naturally endemic to chaparral regions or deserts. Many of the native species naturally exhibit remarkable drought tolerance. Once established, they might not require any more moisture than they get from annual rainfall. Some prefer dry conditions.

Drought tolerance should not imply that such plants are undemanding. In some regards, they are more demanding and less adaptable than plants that require frequent watering. Such plants rely on extensive root dispersion to procure the moisture they require within dry situations. Most do not adapt to confinement, even if watering is enough to cause rot.

Container gardening is therefore a fad that is incompatible with drought tolerance. It only uses less water for plants that use more water. Also, modern drip irrigation, which is very practical for plants that rely on irrigation, requires a bit more effort for plants that use less moisture. To not promote rot, emitters must move farther from main trunks as plants grow.

Many of the most sustainable and drought plants are old fashioned sorts that became too common years ago. Fortunately, some are regaining popularity again. Some of the more compact eucalypti are proportionate to modern gardens. Grevillea, bottlebrush, rockrose, juniper, rosemary, salvia, lavender and New Zealand flax are as drought tolerant as they had always been.