Burying ollas (“oy-yahs”) or clay pots filled with water in the ground is a technique used by early farmers in Northern Africa to irrigate their crops. There is also evidence that the method was also used in early China.
The pots used are made from low fire terra cotta clay and are porous enough to let water pass through when buried. Water flow rate depends on various factors including the amount of plant available water in the soil and the rate at which the plants’ roots absorb water.
The olla irrigation system is so practical that it is still being used today particularly in places like India, Iran and Brazil. It is perhaps the wisest way to water a garden.
Basically, the olla is buried in the ground with only the opening showing above soil level, it is then filled with water. The plants adjacent to the clay pot will then get water from it whenever they need it.
Use Only Unglazed Clay Pots
To make this work, use only unglazed clay pots. The microporous walls of the olla do not allow water to freely flow out. Water will flow outward only when the soil surrounding the clay is less saturated with water. When the soil is fully saturated and there is plant available moisture, the water in the olla will stop flowing outward.
You can check if a clay pot is porous enough. Fill it with water and observe if the surface becomes moist or damp. If it does, then you can use that pot to irrigate your garden plants from under the soil.
Clay pots with bottle or tapered shapes are commonly used.
But you can also use other unglazed clay pots like two planter pots glued together at the mouth.
Eventually, the roots of adjacent plants will find their way to the olla surface and attach themselves to it. They will then draw water from it whenever they are thirsty. When this happens, even less water is wasted due to evaporation because it will go directly to the plants.
When ollas are dug up, they are usually covered in a cluster of roots.
Advantages of Using Ollas
The main advantage of using ollas to irrigate your garden is: less water is used. It uses only half as much water as surface watering which loses a lot of water through run offs and evaporation.
Ollas save even more water than drip irrigation. With drip irrigation systems, some water can still be lost through evaporation. And a drip system is more likely to clog than ollas. Olla irrigation is so effective that it enables adjacent plants to use almost 100% of the applied irrigation water.
Irrigating the garden with the use of ollas solves many problems for gardeners. If you cannot irrigate frequently, that is not a problem. Simply install the clay pots where needed and keep them filled. The plants will be provided with all the water they need when they need it. This method is also perfect for plants that should not be watered frequently.
Ollas are also more environmentally friendly. It is a sustainable way to keep your plants irrigated.
And since the surface soil is kept dry, the growth of weeds is deterred, so less weeding is necessary. But because of this, plants that are being grown directly from seeds cannot benefit from the ollas. You can plant seeds but you have to surface water them until the plants’ roots have grown enough to draw water from the ollas. Transplanted seedlings with established roots will be fine though.
You can add compost tea or liquid fertilizer to the water in the olla and it will be distributed to the plants. Be careful of particles though because they might clog the pores. Also, if you are using greywater or rain water, make sure you filter it first before filling the ollas.
Ollas can be used on raised beds and containers. Just choose clay pots with smaller diameters.+
Size and Spacing
The size of ollas to use will depend on the size of your garden as well as the water needs of your plants. Use deeper ollas for deep rooting plants and use shallow ollas for shallow rooting crops.
An olla can water outwards a distance that is approximately the same as its radius.
So the water spread diameter or the maximum outward distance that water seeping out of the clay jar can reach is approximately two times the diameter of the jar.
Based on this, the space between ollas should be equal to the water spread diameter.
Add water daily or every couple of days depending on the size of the clay pots and on how much water your plants use. Do not let the water level drop too low to avoid mineral buildup on the sides of the ollas that can clog the pores.
Put a lid on the opening of each olla to prevent evaporation and to keep insects like mosquitoes from breeding. Also, mulching around the ollas will further lessen the risk of water evaporation.
Depending on the type of clay the olla is made out of and the quality of water being put in it, an olla should be usable for up to 2 years at least.
Ollas are best used to water herbaceous plants. Woody plants have thicker and stronger roots that might break the clay pot.
You can buy ollas from your local gardening stores or online. If you are handy with the wheel, you can even make your own.
Some Important Notes
- Dig up ollas in the winter. Freezing temperatures can crack and damage buried ollas.
- Do not situate ollas near shrubs or trees or any woody plant with roots that could crack the clay.
Featured image credit: permaculturenews.org