Use of low-fired, clay ceramic vessels (ollas) is an ancient technique for the efficient irrigation of crops. Used in regions of China and North Africa more than 4,000 years ago, the technique has spread throughout arid regions of the world. The use of ollas (pronounced oh-yahs, the Spanish word for “pot”) can save the gardener time, energy, and water. Plants watered in this way do not undergo stress cycles due to water.

A clay pot is buried with only the opening on top visible above the soil surface and filled with water. The porous walls of the unglazed earthenware allow water to dissipate into the soil as needed. Because the pores in the clay pot are small, the water does not freely flow out of the pot. A suction force is created by “soil moisture tension”. If the soil is dry, the water inside the olla will release faster as the dry soil and thirsty roots “pull” water out. Likewise, if there is a saturating rainfall, the water in the olla will remain until the surrounding soil dries.