CAPTION: An ancient irrigation method uses ollas, unglazed clay pots, to water plant life. ATTRIBUTION: Sam Howzit (Flickr)
Ollas are ceramic jars, usually unglazed, used for cooking soups or stews, for storing water or dry foods, or for irrigation purposes in gardens. As water is able to seep through the unglazed walls of an olla, these pots are buried underground next to the roots of the plant that needs irrigating. The neck of the olla extends above the soil and is filled with water, which gradually seeps into the soil to water the roots of the plant. Ollas are especially useful in areas of drought, such as California and in desert climates. It is an efficient irrigation method, as no water is lost to runoff or evaporation.
History of the Olla
Chinese agriculture references using ollas for irrigation as far back as 2,000 years ago. Evidence shows that this technique existed and was practiced in places around the world, including Brazil, Zambia, Iran, Mexico, Pakistan, and India. It is believed that the Spaniards brought the practice of using ollas as a water-conserving method to the Southwest region of the United States. It was originally designed for desert or semi-arid regions of the world.
How to Use an Olla
Using an olla is relatively simple and involves burying an unglazed pot in soil, leaving only the neck exposed. Seeds or the plant you wish to irrigate are then planted within 5 inches of the pot. Simply fill the olla with water and let it do its work. Over time, the water gradually seeps through the porous clay, irrigating the plant’s roots. The roots will gradually surround the jar to absorb moisture. The rest of the soil remains dry, reducing weed germination and compaction. Ollas provide a steady flow of water to plants and reduce the need for frequent watering.
Benefits of an Olla
Ollas are highly efficient, as the water stops seeping out of the pot once the surrounding soil has reached a healthy moistened state. Once the soil begins to dry out again, the water then continues to seep out. This means that the soil will always have an optimal amount of moisture without the risk of compacted soil or root rot. As the roots grow to reach the pot, they pull water directly from the pot as the plant needs it. This creates an environment where nearly no water is wasted. Ollas also lessen the amount of work for gardeners: As the olla is underground, the topsoil is able to dry out, creating a crust that most grasses and weeds can’t push through.
Make Your Own Olla
As finding homemade ollas can be difficult, many gardeners prefer to make their own using unglazed terra-cotta pots. Use a water-proof glue to secure the pots together at the mouths. Plug the bottom hole by gluing a scrap piece of unglazed pottery or tile over the hole. Be sure to test your pots before buying them by filling them with water and checking for leaks around the seams and bottom. Once they are buried, use a rock or another piece of tile to cover the top hole. This reduces evaporation further and helps to keep out mosquitoes and other garden pests.