May 28th, 2009

Dueling Vegetable Beds: Experimenting with Ollas

The area of Central Texas where I live is under severe drought restrictions. Our well draws water from an underground lake called the Edwards Aquifer which requires rain to fall in a specific recharge zone for it to refill. Because of the dry conditions over the last few years, the aquifer is drastically low.

To help ensure there is enough water to go around, our water conservation district is limiting ground water users to 3,000 gallons per person each month along with other restrictions such as watering plants by hand only. To help lower our water usage, I’ve started experimenting in the garden with ollas.

Ollas

Ollas (pronounced oh-yahs) are one of the oldest and most water efficient irrigation techniques available. Ollas are unglazed ceramic water pitchers buried near the root zones of plants. Instead of watering the plant directly, you fill the olla. The water slowly seeps through the clay walls of the olla as the roots take it in. Unlike traditional irrigation techniques, very little water is lost to evaporation and runoff.

As a small experiment, I planted two beds this spring with identical vegetables – one with ollas and a control bed without. As ollas are hard to find locally and are a bit pricey with shipping, I made my own out of terra cotta pots and silicone.

Making Ollas

Olla supplies

Olla-making supplies: Unglazed terra cotta pot (2 per olla), tile, silicone.

Olla with tile over hole

To seal the bottom hole, I used a peice of broken tile glued in place with silicone.

Olla with tile over hole

Two pots are then glued together for each olla leaving the top hole open for filling.

Ollas vs. Hand Watering

Both beds in the experiment consist of three different tomato varieties with bush beans in between. Both beds were dug and prepped the same way and I’ve added organic fertilizer to both identically.

When I first planted the tomatoes, I hand-watered all of them during the first week to get them established. Depending on rain, I now fill the ollas and hand-water the rest of the tomatoes about every ten days. I’ve never watered the bush beans.

Olla in the vegetable garden

Olla buried in the garden. The shell covers the top hole to help prevent evaporation – you can also use a flat rock.

The ollas take less time to fill (and therefore less water) than it does to water the rest of the tomato plants. I don’t see any real difference in the health or size of the plants – in fact, the tomatoes on the non-olla row are a bit taller. Both seem to be producing about the same amount of fruit.

Fortunately, we’ve had a decent amount of rain in the last month and I haven’t had to water much. I think the real test will come during the longer dry spells that we typically see in July and August. Despite the recent rain, the drought is expected to continue.

More Information on Ollas

Where to Buy Ollas in the U.S.