-
- Articles
Index : Landscaping Design
-
-
- 9. Plant Hardiness Zones - Top
The first step in determining what garden and landscape plants grow in the Tucson area is to look
to the plant hardiness zone maps. We have two to choose from. One is the U. S. Department of
Agriculture Hardiness Zone map, used by much of the country. The other is the the Sunset
Western Hardiness Zone map, which includes the area west of the Rocky Mountains.
The USDA hardiness zone map is based on winter minimum temperatures and little else. This is
fine for relatively flat areas of the country, where topography has little effect on climate. It also
works well where average annual rainfall tends to be rather uniform. But in the western region of
the country elevations and rainfall amounts fluctuate radically, even within the same localized
area. This has a major effect on temperature ranges, length of growing seasons, and plant
adaptability. For this reason, Western climate zones were developed by Sunset Publishing in
cooperation with the University of California.
Using the Sunset Western climate zone map, Tucson is in zone 12, described as the intermediate
desert. The elevation range in this zone begins where the low desert ends, at 1500 feet, and
extends up to 3300 feet, where the high desert begins. This zone is considered semi-arid, with
annual rainfall supporting lush desert growth. Growing seasons are long, averaging 8 months
between frosts, and 9 months between killing freezes (28 F).
The Sunset Western Garden Book lists over 6,000 species of garden and landscape plants and
their hardiness zones. There is also a CD version of the book, in which a plant search can be
conducted by hardiness zone.
Most plant reference books do not list Western hardiness zones. However, by cross-referencing
with the Sunset Western Garden Book, the hardiness zone for any given plant can be determined.
Mail order garden catalogs almost exclusively use USDA hardiness zone designations. Here in
Tucson we are in zone 9, which distinguished by average minimum temperatures from 20 to 30
F. A common mistake in ordering plants is to select from colder hardiness zones, 8 or lower.
These plants would be able to withstand our cold, but not our summer heat and drought. Plants
in colder hardiness zones also often have cold dormancy requirements. For instance, certain
fruiting plants, such as raspberries, must have a minimum number of chilling hours during the
winter. If they do not receive this cold, they will not produce fruit and the plants will eventually
die.
Select fruit varieties adapted to our climate. Many varieties of apples are advertised to grow in
zone 9, but only two, Anna and Dorsett Golden will adapt to the Tucson area. Other deciduous
fruit trees such as peach, apricot, plum and pear have a limited number of varieties which will
grow in our zone 9 conditions.
Some plants may have they cold dormancy requirements met in zone 9, but still may be unsuited
to the desert. An example is the red maple tree (Acer rubrum). It is advertised for zones 3-9, and
will grow in eastern regions of zone 9 where rainfall and humidity is high. It will not grow
successfully in our zone 9 desert!
Some plants listed for zone 9 may not be adapted to our soil conditions. Mountain laurel and
gardenia are listed for zone 9, but both require an acid soil. Our very alkaline soil causes these
plants to turn yellow from iron and other micro nutrient deficiencies. Both need rich, moist,
organic soil and lots of moisture and humidity. Again, a bad choice for Tucson.
In determining a plants adaptability to our climate, rely on local reference sources. Books written
by authors and about plants of our region can be used. Visiting at local garden centers and
nurseries is always a help. Garden clubs and plant societies can suggest varieties in certain plant
groups, such as roses, herbs, cacti, etc. Recommended plant varieties can also be seen at the
Tucson Botanical Garden, Tohona Chul Park, and the Sonoran Desert Museum.
The Pima County Cooperative Extension operates Master Gardener Plant Clinics in Tucson and
Sahuarita were information on recommended garden and landscape plants can be found. Master Gardeners are available Monday through Friday from 9:30 am to 3:30 pm in Tucson by phoning 626-5161 and Monday, Wednesday, and Friday from 9:00 am to 1:00 pm in Saharita by phoning 648-0808.
- Updated: July 26, 1998
-
-
[e-Mail me
the Articles] - [Search
the Articles]
-
|
