The ancient garden watering system is still the best

I’ve appreciated drip technology for many years and used it extensively in California, where an historic drought created ultra-dry conditions for years until finally breaking last winter.

Drip systems were invented in 1959 at an Israeli kibbutz. They’re inexpensive and easy to install. But there’s another watering technology that’s even easier to use, been around for millennia and saves just as much water. It’s called the olla pot (pronounced “oh-ya”).

I spoke with Benita Middleton, a professional gardener for more than 20 years who received her Royal Horticulture Society training at Sparsholt College in the United Kingdom. She and her team of gardeners use olla pots routinely.

I also consulted with Bryan Clayton, CEO of the lawn care company Greenpal and a self-described advocate of olla pots. Here, these experts explain how and why olla pots work.

What Is an Olla Pot?

A classic olla pot is an unglazed clay pot with a rounded shape that tapers to a thin neck. You bury it in the ground up to the neck, fill it with water, then covering the opening to prevent evaporation. Because clay is porous, water seeps at a controlled rate into the surrounding ground, nourishing the roots of plants close to it.

Olla pots come in various sizes. A good-sized one with a 12- to 18-inch diameter holds two to three gallons of water and will nourish plants within a three-foot radius. When planting a container garden with limited space, you’re better off with a smaller pot. Just be sure your plants are close enough to the pot to benefit.

“Olla pots can cut down water usage by up to 70% compared to traditional watering methods,” Clayton says. “That’s significant!” Adds Middleton: “If growing plants where there’s very little rainfall, then olla pots are an efficient, environmentally friendly way to water plants.”

Who Invented the Olla Pot?

It’s not clear who invented the olla pot.The Latinized name suggests it originated in Mesoamerica, or perhaps Southern Europe. Not so, according to Middleton. “Olla pots originated from North Africa and China more than 4,000 years ago,” she says, “and the technique has spread throughout arid regions of the world.”

Olla pots are mentioned in the Fan Sheng-chih Shu, the world’s first agricultural text that dates back 2,000 years to ancient China. But the text doesn’t use that name. The Romans established the term “olla,” referring to a rounded pot normally used for cooking and carrying water.

How To Use an Olla Pot

Burying an olla pot is easy. The largest ones require a hole about 18 inches deep by 18 inches wide, which takes only a few minutes to dig with a shovel. You can bury smaller ones with even less effort.

Leave the neck protruding a few inches above the ground to make it easy to see. Fill the pot with a garden hose or watering can, and place a clay plate or some other cover over the opening.

Soil moisture tension pulls water through the porous sides of the pot and keeps the soil around the pot wet. An olla pot stops releasing water once the soil is saturated, so the plants you group around the pot never get over-watered.

You’ll need to monitor the water level in an olla pot and refill it as needed.

“Refilling the ollas depends on the soil type, planting density and weather conditions,” says Middleton. “The frequency can vary from once a week to every other day.”

It’s a good idea to add water when the pot is half-full instead of empty, because that prevents salts in the water from clogging the pores. If the pores should clog, simply fill the pot with vinegar, let it sit for a few hours and rinse it thoroughly. Plants don’t like vinegar.

Where Can You Use Olla Pots?

“The best climate zones to use ollas are hot dry regions where there is very little rainfall,” says Middleton.

You can use ollas in containers as well as in the ground, but keep in mind they work best in loamy, absorbent soil. If there’s too much clay, or the soil is loose and sandy and drains too quickly, moisture won’t spread to nearby roots. In some cases, amending the soil with compost or adding several inches of topsoil may be necessary for a healthy garden.

Where To Buy an Olla Pot?

Olla pots are sometimes difficult to find in garden centers, but they’re readily available online. They typically cost between $15 and $40, although the largest ones might run a little more.

Make Your Own Olla Pot

Here’s how:

Seal the drainage hole in a terra-cotta pot with epoxy, invert a second terra-cotta pot over the first and affix together with epoxy or silicone caulk. Be sure to make a completely watertight connection. Then bury the pots, leaving the drainage hole of the second one open to add water. Don’t forget to cover the pot once it’s full.