By Guest Author Mary Kathryn Dunston
No matter how much we know about gardening, there is always something new to learn. And sometimes the newest ideas hail from years gone by. What I’m talking about here is clay pot irrigation, a technique which originated thousands of years ago. We know this because clay pots, called ollas, have been found in archaeological digs around the world.
What is an olla pot and how does it irrigate you garden?
An olla is a low fired terra cotta pot that is buried neck deep in garden soil, a raised garden bed or container. It is then filled with water and plants are planted around the olla.
As the roots of the plants dry up the soil, a phenomenon called soil moisture tension is created. This causes the dry soil to literally draw the water through the walls of the porous clay pot. The most efficient ollas have a bulbous bottom and a neck that is wide enough to make filling and checking the water level easy. A lid of some kind is important because it keeps the water in the olla from evaporating and keeps out frogs, mosquitoes, and other unwanted visitors.
What is soil moisture tension?
We know that an olla pot waters your garden by soil moisture tension, but what is that exactly? The best example is to picture a dry paper towel touching a puddle of water. Without you doing anything, the dry paper towel will start absorbing the water, until the paper towel is saturated. In the case of the water-filled olla, the soil is the dry part, and it will pull the water out of the olla until the soil has all it needs – the soil won’t be saturated, but it’s sufficiently watered. And since the roots of a plant are steadily absorbing the water from the soil, the soil replenishes its water supply by continually pulling from the clay pot. That is perfect supply and demand. Your job is to check the olla every 3-7 days to see if it needs water. Now that’s simple!
You now know about filling ollas and having the dry soil pull the water through its porous walls. Yet, if your weather forecast is threatening rain, rain and more rain (which can split tomatoes and melons), don’t put water in the olla. From above, the empty olla pot is just a hole in the ground, and since water always runs downhill, gravity will refill that olla with excess rainwater.
The benefits of olla pots
The benefit of ollas is that they conserve water – up to 70% compared to topical watering since they are buried up to 1 foot in the ground (the bulbous part). For folks on city water, that is a money saver. The saving occurs because the water-filled olla is so deep it greatly decreases the evaporation rate. This also encourages plants around it to grow a large root base, since the roots get water as they need it.
Another plus is that this deep watering system does not feed surface seeds, so weed growth is greatly decreased. By how much? That depends on personal garden maintenance. I think of weeding like dusting a house. Some people don’t mind a little dust (or weeds), others like a super tidy house (or garden). But no matter how you like things, less surface water means less weeds can grow, and that’s a good thing! Having said that, many people plant starter plants around their olla pots, but if seeds are planted, it would be necessary to water your seeds until their root system can benefit from the clay pot irrigation. That usually takes several weeks, depending on the plant.
How much of your garden can an olla pot water?
How far an olla waters depends on its size – the larger the olla pot, the further out it can water. Ollas range from 1 quart/liter to 2.9 gallons/11 liters and traditionally, smaller versions were for smaller plants, since the roots of small plants don’t grow very deep. But today, smaller ollas are often used in containers and the larger models are used in the ground, raised beds, and large containers. The largest olla will water a 3 foot circle in many soil types. The watering radius decreases as the olla’s size decreases.
What plants can I water with an olla?
Any plant can be watered with an olla. Larger vegetables, such as tomatoes, need plenty of room to grow, so most people put 3 tomatoes and one companion plant (basil, for example) around one large 2.9 gallon/11 liter olla. Newly planted trees and shrubs can also benefit from olla pots. 2.9 gallons of water will last for days next to a new tree, helping it get through that first year. After the first year, dig up the olla and relocate it.
A well made, thick-walled olla pot will withstand extreme temperatures and can be left in the ground through the winter (but make sure it’s free of water before the first frost). Some ollas are more delicate, so if you live in a cold region, take note of the limits of the olla you purchase.
Olla pot maintenance
Ollas are really easy to maintain. If you hand till your garden, you can bury your olla next to peppers or tomatoes, or tuck them into squash hills and call it a day. Thick walled olla pots are tough enough to withstand some sloppy shovel action, but a tiller bland is asking a bit much of terra cotta. If you machine till your garden, it would be wise to pull your ollas up every season, or carefully till around them.
If your water is heavy on minerals, as some wells are, every few years you may need to soak your ollas in a mild vinegar solution for a few hours and then scrub the outside. Then soak with clear water to rinse.
If you see debris in your olla, overfill it with water, and allow the debris to flush out or dig it up, turn it on its side and wash it out.
I have personally left my ollas in the ground (35 of them), filled them with well water and hand tilled around them for over 5 years, and they perform without trouble. I am in Zone 7a. I have heard many stories of olla users from Canada to Southern California, and Washington State to Florida, who have enjoyed the simple watering system of clay pot irrigation. They have discovered this ancient way of watering and benefited from this simplistic, organic system. If you have a busy life, want to ease up on watering time, or just enjoy making life simpler, try gardening with an olla. You won’t be disappointed. Happy Olla Gardening!
For more information, see:
- Action sheet on buried clay pot irrigation from the Pan African Conservation Education Project.
- This article on Ollas from PermacultureNews.org
- This research study on buried clay pot irrigation
Author bio: Mary Kathryn Dunston has helped develop the company Dripping Springs Ollas She has been gardening since the Hippie movement (she was very young), and gets great joy from teaching people a healthy, organic, water-wise way to grow food for themselves, and their neighbors! She can be reached at mk@drippingspringsollas.com.