This may look like a plain old clay jar to you, but it’s really an Olla (pronounced oi ya), an unglazed clay pot, buried among plants and filled periodically with water. This ancient watering system was brought to the Southwest by Spanish settlers and was adapted by Native American gardeners. Here’s how an olla works: Water seeps through the clay, and plant roots grow around the urn, clasping the container to absorb its leaking moisture. The open end of the olla extends above ground so the urn can be refilled as water is absorbed. You can place a small rock in the neck of the ollas to avoid evaporation.
Olla irrigation virtually eliminates runoff and evaporation, allowing
the plant to absorb nearly 100 percent of the water. Modern systems, including drip irrigation, lose water to evaporation, and they tend to clog. Olla gardening also helps gardeners who can’t irrigate frequently because of water conservation ordinances or time constraints. We are happy to offer these for sale at Southwest Gardener. A big thanks to Donna at the Arizona Herb Association for connecting us to a terrific supplier.
Ollas will work in the ground, raised beds or in pots. Here are pictures of them being used in an urban garden setting.
Curtis W. Smith, an extension horticulture specialist at New Mexico State University makes these recommendations.
- Choose low-water-use, non-woody herbaceous plants. Woody plants can break clay urns as their roots grow in diameter.
- Match olla size, and shape to plants’ water needs, root size and root distribution.
- Cluster ollas and plants to maximize water-use efficiency.
- Match olla diameters with the diameter of plant clusters. Use shallow, broad ollas, for clumps of grasses and annuals.