Pittman Area of Las Vegas and Managing its Soil

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.

Most native soils in that area are 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.