In brief
Irrigation with an unglazed clay pot buried up to its neck and filled with water, which seeps slowly through the porous wall into the soil around the roots.
What is olla irrigation?
Olla irrigation is one of the simplest ways of bringing water to plants: an unglazed clay pot is buried next to them up to its neck, filled with water and closed with a lid. The fired clay is porous, so the water seeps slowly through the wall into the surrounding soil. There it forms a moist zone around the pot, from which the roots of the neighbouring plants drink. The surface of the soil stays largely dry. The name comes from the Spanish word for pot; in English the method is also called buried clay pot or pitcher irrigation.
The force behind it is the difference in moisture between the water in the pot and the soil around it. Dry soil draws water through the pores of the clay; moist soil draws less. The release therefore adapts, within limits, to how much the plants take up. That is the main difference from a watering can or a hose, which deliver a fixed amount at the surface regardless of what the soil needs.
The method is old. David Bainbridge, who in 2001 published an overview of buried clay pot irrigation in the journal Agricultural Water Management, described it as little known but very efficient, and in a later interview spoke of its use for more than 2000 years. He gathered reports and trials from several continents.
What the studies show
The evidence on water savings is real but thin, and it has to be read carefully, because results depend heavily on what the pots are compared with. In the same interview Bainbridge cites a trial with melons in India in which buried pots achieved yields of about 25 tonnes per hectare with only about 2 centimetres of water, while flood irrigation achieved 33 tonnes with 26 centimetres. The yield was lower, but each litre produced far more.
A more recent controlled trial comes from Rwanda. Hatungimana and colleagues compared buried clay pots with drip irrigation for cabbage and published the results in 2023: the clay pots used about 40 percent less water than drip irrigation, and their water productivity, the harvest per cubic metre of water, was clearly higher. Even here a single trial with one crop on one soil stands behind the figure.
From such studies one can conclude that ollas can use water very sparingly. A general percentage of savings for every soil, climate and crop cannot be derived from them, and claims of fixed savings in gardening literature should be read with that caution.
Limits in practice
An olla waters only a limited volume of soil around itself. It therefore suits single plants, young trees and small beds, not whole orchards or fields. Every pot has to be refilled by hand, in hot weather every few days, in milder weather about once a week. The clay can crack, and frost destroys pots that still hold water. Fine roots grow towards the moist wall and can wrap tightly around the pot, which can make it hard to remove later. Only unglazed clay works, because a glaze seals the pores. On a large scale, the cost of the pots and the labour of filling them quickly become the limiting factor.
How Terra Humana understands it
For Terra Humana the olla is a tool for the establishment phase. On a slope with five dry months a year, the first and second summer decide whether a young tree takes root. An olla next to it, under a layer of mulch, can carry it through this time with little water, especially where water has to be brought by hand.
At the same time the olla should remain a bridge. The goal of drought-tolerant planting and rainwater harvesting is land whose plants live on the winter rain stored in the soil. An olla that is still needed after years shows that the site, the species or the soil are not yet in balance. It helps most when it makes itself unnecessary: when the roots have followed the moisture down into the depth and the pot can stay empty.
Frequently asked
What is an olla?
An olla is an unglazed, porous clay pot that is buried up to its neck in the soil next to plants and filled with water. The word is Spanish and simply means pot. Because the fired clay is permeable, the water seeps slowly through the wall into the surrounding soil, where the roots can take it up. The opening stays above ground and is covered with a lid or a stone, so that little water evaporates and no animals drown in it. The method is also known as buried clay pot or pitcher irrigation.
How does olla irrigation work?
The water moves through the fine pores of the clay towards the drier soil. The drier the soil around the pot, the stronger this pull; when the soil is moist, the flow slows down. Descriptions of the method therefore say that the release follows the water use of the plants to some degree. The water arrives below the surface, directly in the root zone, while the surface itself stays largely dry. That reduces evaporation and gives weeds less moisture than watering from above.
How much water do ollas really save?
The evidence base is small, and the figures depend heavily on what the pots are compared with. In a trial with cabbage in Rwanda, published in 2023 by Hatungimana and colleagues, buried clay pots used about 40 percent less water than drip irrigation and achieved higher water productivity. David Bainbridge, who reviewed the method in 2001, cited much larger differences compared with flood irrigation in a 2010 interview. Such results come from individual trials with particular soils and crops; a general saving percentage cannot be derived from them.
What are the disadvantages of ollas?
An olla waters only a limited volume of soil around itself, so it suits single plants or small beds rather than whole orchards. Every pot has to be refilled by hand, depending on weather and size every few days to once a week. The clay can crack, especially when water in it freezes, and fine roots can grow tightly around the pot. Only unglazed pots work, since a glaze seals the pores. For large areas the cost and the labour of filling quickly become a limit.
When are ollas useful in a dry climate?
Ollas are useful where a few plants have to be carried through a critical period with little water: young trees and shrubs in their first summers, a small vegetable bed, a planting far from any pipe where water has to be brought by hand. Combined with mulch, which keeps the soil surface cool, they make every litre count. For a planting meant to become independent of irrigation, an olla is a bridge rather than a permanent solution: the aim is for the roots to grow down to deeper moisture.
Related terms
See this in practice
Sources
- Bainbridge, D. A., Buried clay pot irrigation: a little known but very efficient traditional method of irrigation, Agricultural Water Management 48(2) (2001) 79 to 88
- Hatungimana, J. C., Niyigaba, J. B., Kwitonda, T. S. and Tuyishimire, P., Water saving and water productivity under buried clay pot and drip irrigation systems for cabbage in Rwanda, African Journal of Food, Agriculture, Nutrition and Development 23(3) (2023)
- Bainbridge, D. A., Beyond drip irrigation to water fields in dry land areas, interview, Resilience.org (2010)
Last updated: 2026-10-12