Olla irrigation: water below the surface

How it works

An olla is an unglazed clay vessel buried with its opening accessible above the soil. Water moves through its porous walls into the surrounding soil. The University of Arizona describes it as an option where conventional irrigation is impractical. It still needs monitoring and refilling. [1]

Set up a small trial

1. Choose a sound, unglazed vessel that holds water without an open drainage hole.
2. Bury it with the filling opening exposed. Firm soil gently around it so the walls contact soil.
3. Fill it and cover the opening to reduce evaporation and keep debris and insects out.
4. Water seeds and new transplants separately while their roots establish.
5. Check water level and nearby soil moisture frequently at first.

These steps draw on university extension guidance. Refill needs vary; a fixed promise such as “once a week” is not reliable for every garden. [2]

Measure the useful wetting zone

Our suggested local trial is one small bed before a larger purchase. After filling, inspect soil at several distances and depths without disturbing the crop’s roots. Record which plants remain adequately supplied.

Use a notebook with five columns: date, litres added, rainfall, soil observations and plant condition. Compare with a similar bed using your usual watering method. Keep crop, mulch and exposure as similar as practical. This is a learning exercise, not a guarantee of a particular percentage saving.

Understand the limitations

Pots occupy growing space and may crack. Salts can obstruct their pores, and woody roots may damage them. Seedlings can need supplementary watering before reaching the moist zone. Arizona’s guidance also notes that ideal spacing is not firmly established for every situation. [1]

For a large area, compare the time needed to refill pots with other irrigation options. Base that decision on your measured labour, water use and crop response.

Sources & further reading

1. University of Arizona — Irrigating with Ollas
2. University of California ANR — Olla Irrigation

The supplied Olla Pots PDF is a video pointer. This draft uses the accessible university guidance below; it does not claim to summarise the unreviewed video.