Drought-tolerating ornamentals are effective in integrating the surrounding natural dry-type landscape. They require little water or maintenance and include both native and introduced plants from similar dry climates. Drought-tolerating plants are either drought resistant or drought evading, with drought resistant plants remaining green during dry periods through traits like small, thick leaves and deep roots, while drought evading plants reduce water needs by shedding leaves or storing chlorophyll in stems.

1. Drouaht-Toleratina Ornamentals
U u ~ ~ ~-~ -
natives and introductions from like climates require little
water o maintenance and are adaptable to rural landscape
r
Robert 5. Deering
Drought-tolerating plants are useful pending upon the climatic conditions and Many ornamentals-both native and
for landscaping areas which do not nor- what percentage of available soil mois- those which have been introduced from
mally receive irrigation water. They are ture is present. A plant which grows well similar climatic regions-are drought re-
especially adaptable to the rural home in a coastal habitat, for example, may sistant. These plants differ physiologi-
landscape because there is usually suf- not survive in the hot-dry interior valley. cally, in many respects, through the man-
ficient space for them to grow in areas Heat and desiccation by frequent hot-dry ner in which they survive the drought
which will not receive summer water. winds discourage all but the toughest and period.
They can be valuable as windbreaks and hardiest of plants grown with little or A true drought resistant plant is a
screens for buildings and machinery. no water. The tender and succulent foli- perennial-ither woody or herbaceous
Native woody plants-often colorful age types rapidly dehydrate under these -which remains green or in a vegetative
and useful as ornamentals-have not conditions and have considerable diffi- state during the dry season. Such plants
been fully appreciated as landscape culty in surviving. generally have small, thickened, leathery
plants. Frequently, of course, because A number of factors-such as depth or waxy leaves, such as the native Cali-
they have adapted themselves to extreme of water table, salts and alkalinity, soil fornia lilac-Ceanothus species. Large
drought conditions-and are conse- types, maximum and minimum night and broad-leaved types are uncommon.
quently susceptible to fungus diseases day temperatures, precipitation, evapo- Drought-resistant plants usually have
when the soil is warm and moist-they ration rate-determine the adaptability deep penetrating root systems, low rates
are incompatible with other garden of a plant to an area. Plants come through of transpiration, and perhaps a greater
plants. Under natural conditions, how- the drought period either by resisting capacity to use dew for additional mois-
ever, diseases of this kind are less likely the adverse conditions or by evading ture. Experiments have shown that
since the plant receives little or no water them. Many plants commonly considered drought-resistant plants also have special
during the warm season, and conditions drought resistant may actually be genetic characteristics which enable them
for their spread are less favorable in the drought evading. Actually most annual to survive under adverse conditions. The
cold rainy season. plants are drought evading but these are Eucalypti-introduced from Australia-
Drought-tolerating plants are either of little importance in permanent land- are good examples of foreign plants well
drought resistant or drought evading, de- scape plantings. adapted to California conditions.
Drought evading plants may have few
Drought-toleratingornamentals are effective in integrating the -if any-leaves which they may retain
surrounding natural dry-type landscape. only during the wet season or when there
is sufficient soil moisture. Those with few
leaves-or none-often carry the chloro-
phyll in other parts as well. The cacti,
for instance, carry the chlorophyll pri-
marily in the stems and trunk; and the
Jerusalem thorn-Parkinsonia aculeata
- c a r r i e s it in the rachis of the leaf and
in the bark of branches and trunk.
Also in the drought-evading group are
broad, thin-leaved plants, such as the
California Buckeye-Aesculus calijor-
nica-which have developed special
methods for survival. The large hand-
some leaves of the Buckeye are produced
in early spring and remain only until
midsummer when soil moisture is not
sufficient to support this type of foliage.
The plant then goes into an early dormant
condition until the following spring.
The water requirements for both
drought-resistant and drought-evading
plants are small relative to the climatic
area in which they grow. Perhaps their
greatest virtue-aside from the saving
of much valuable water-is that they re-
quire little in the way of maintenance.
Robert Deering is Assistant Professor 01
Landscape Management, University of Califor-
nia. Davis.
CALI FOR N I A A G R I C U L T U R E , SEPTEMBER, 1956 15