Castles and Moats for Smart Drought Irrigation

Jessica Dowell

Plant Basin-flat3

Diagram of a “Castle and Moat” plant basin by Jessica Dowell.

Have you tried dumping dish water on your plants just to watch the water flow away from the plant? If so, try using the castle and moat plant basin method. Whether watering your garden by capturing water from your kitchen sink or installing drip irrigation, good plant basins make a big difference. Basins capture water, rain or otherwise, and allow it to sink in around the plant’s roots. It is conceptually similar to mulch basins used for “Laundry-to-Landscape” grey-water systems or rain gardens. With the continuing drought it makes sense to give our plants all the tools we can to make the best of the little water available.

Example of a Castle-and-Moat plant basin on a slope by Jessica Dowell.

Example of a Castle-and-Moat plant basin on a slope by Jessica Dowell.

When working with people unused to building basins when installing plants, I like to compare the structure of the basins like a castle surrounded by a moat. The moat is then backfilled with mulch. The mulch leaves space for water to fill up and soak into the soil around the roots. Basins can take a variety of forms depending on your soils and slope. For example, if you have heavy clay soils then your plant should be set on a hill about one inch overlooking its moat above the surrounding soil. For most soils though, the plant should be set at the same elevation as the soil around it and the moat is dug 3- 12 inches from the root ball depending on the size of the plant and your soils. I like to dig my moats wider than deeper but adjust to the space available and your site. Castles and moats work for sandy soils too. In that case, the organic matter backfill ends up being the source of moisture holding. The most important thing is to avoid putting your plant at the bottom of a bowl. Even with the little water available, it can rot your plant. The same is true if your soils are poorly drained and are left to create a berm, impeding water flow.

For illustrations of this method, I like Caltran’s details for plant basins (2010 Standard Plan H3 ). They are simple and available to the public.  You can also find out more at the Arbor Day Foundation  and from Master Gardeners. In fact, here is an El Dorado Master Gardeners slide presentation  (link opens as a large pdf) on harvesting rainwater and greywater use from CNPS El Dorado Chapter president Alice Cantelow.

As always, experiment and adapt to your site and needs.

Ever wonder where Irrigation Management data comes from?

CIMIS logo

Introducing CIMIS – which is the California Irrigation Management Information System.

CIMIS plays a big, hidden role in our gardening lives – and in the future you will hear more about it. It is a statewide program in what is called the Office of Water Use Efficiency (OWUE). This “efficiency office” is part of California Department of Water Resources (DWR), which in turn is part of the Natural Resources Agency.

CIMIS manages a network of over 120 automated weather stations all over our state. It was originally organized by the water resources people and UC Davis  to assist California’s big water users (agriculture) to manage their increasingly controlled and limited water resources. 

The idea was to figure out how much rainfall a particular area received. The farmer, knowing how much water a particular species needed over a year-long period, would be able to calculate supplemental irrigation needed to keep the plant at optimal health without wasting water.

When we started to help homeowners reduce turf areas and plant with natives, this data was invaluable in making comparisons between native plant needs and the natural rainfall of an area. Match your plant to your rainfall and happiness ensues. It reminds me of the Dickens character, Mr. Micawber defining his life view, “Annual income twenty pounds, annual expenditure nineteen pounds nineteen and six, result happiness. Annual income twenty pounds, annual expenditure twenty pounds nought and six, result misery.”

So, annual CIMIS data rainfall twelve inches, annual irrigation need for Ceanothus eleven inches, results happiness. Annual CIMIS data rainfall twelve inches, annual irrigation need for Kentucky bluegrass thirty-six inches, result misery.