Q. I am a young
gardener (25) in Henderson, specifically Green Valley, near the Pittman Wash. I am interested in the cultivation of plants not only for their
aesthetic value, but their benefit to wildlife as well. This has steered my
interests to pedology and edaphology as well as horticulture and botany.
From what I
have gathered from the USDA soil survey of the Las Vegas Valley (published in
1985), my residence (and therefore garden) lies near a boundary between the
‘McCarran’ and ‘Jean-arizo’ soil series.
From direct observation, it seems I am
situated more so in the McCarran series area. With massive soil in the lower C
horizon, and sticky and plastic qualities throughout, how does this effect
irrigation protocols and amendments types and amounts? The reason I ask
is I recently purchased some premium compost from Viragrow (thanks for the
rec), and want to make sure I use the correct ratio of compost to native soil
to prevent reinforcing any drainage issues associated with clay soils. The
bare, native soil I am about to cultivate drains moderately slowly (some areas
15 minutes, other areas up to an hour). The only plants that have ever been in
there were some poorly pruned Texas Sage (Silver and Green Cloud varieties)
which have been removed. This area was not irrigated for many years, with the
plants subsisting on incidental precipitation and irrigation diffusion from
neighbors’ lots. The irrigation to this area has been repaired, and a large
ornamental and small productive garden is now planned to be planted there. Are
there any good resources, preferably more up to date than 1985, that can
provide more information on local soil series and how to mitigate the
inhospitable qualities of such?
A. You live in
the Pittman area of Las Vegas and Henderson.
 |
| Description of the Pittman soil series in Las Vegas and Henderson, NV. |
classified usually as “heavy” which means they have quite a bit of clay and
smaller silt particles. Water drainage can be a problem in these soils if the
soil is irrigated too often. For this reason, I tell people that if all the
water in a hole on the property drains overnight, it’s okay. If this were
Wisconsin or Iowa then it would be different. Those soils are beautiful
compared to the Mojave Desert soils.
The soils for
subdivisions oftentimes are imported or man-made and may not represent the
native soils in those areas. If you have in imported soil on your property,
then it may not be representative of the soils map. I am very familiar with
NRCS soils maps for Southern Nevada and Northern Arizona, and I know the
McCarran soil series quite well. It represents a huge area. So, make sure you
are actually dealing with the native soil and not one that’s imported. You
should be able to see that from the soil horizons. But overnight drainage for
landscape soil would be okay for most landscape plants. This may not be true of
Mojave native plants. If you are growing Mojave natives then I would suggest
either not using an irrigation controller or using it only to water manually
and not leave it on a schedule.
As far as more
information is concerned, Dr. Dale Devitt (soil science researcher) and I are
in the process of publishing a book that you might take a look at. It’s
available on Amazon in digital form. If you want a hard copy or digital it is
also available from the publisher. Dr. Devitt teaches in the biology department
at UNLV. Dr. Devitt is a “hard” scientist and I consider myself a “soft”
scientist who focuses mostly on transferring difficult information in terms
more easily understood. Together we have published about 40 peer-reviewed
scientific research articles in various journals.
Dr. Devitt is the local soils
expert and knows more than anyone about soils and water movement and plant use
in the Mojave Desert. But honestly the book takes much of this difficult
information from an urban tree perspective and tries to simplify it as much as
possible. It’s really rehashing a lot of the same information but puts it into
one book.
Any of the Cloud series of native plants (Green Cloud, Silver Cloud, etc.) will be sensitive to soils that drain poorly. Their roots will tend to die due to poor drainage. In soils like that, consider planting them on a hill or berm about a foot tall and perhaps about six feet wide. This will give the roots a chance to grow in a raised soil that will drain better.