DIY Ollas for Water Conservation

What is an olla?

An olla (pronounced oh-yah) is an efficient system for irrigation that has been in use in desert regions for thousands of years. It is thought that they originated in Northern Africa, and were brought to America by the conquistadors. Traditionally they are an oval shape with a long neck and made from low-fired clay. It is used to provide water for roots, decreasing excessive evaporation and water runoff.

How do they work?  
An olla is buried in the ground with only the top opening visible and then filled with water.  The water is then distributed to the soil due to capillary action created by soil surface tension. As plant roots use water, the water will be released from the olla into the surrounding soil. When the soil is dry, water will be released faster and when the soil is wet, the water will remain in the olla.   

Why would you use them?  
Use them to promote deep watering which promotes dense root growth, and to promote even watering which prevents cracks in tomatoes and melons. Ollas allow the surface soil to remain dry while providing water to plant roots which may decrease weed growth. Ollas work best for plants that have fibrous root systems such as squash, melon, tomatoes, and chili peppers but can also be used to provide even watering for young trees, vines, and bushes. 

When would you not use them?  
Ollas are not recommended for use with grains or legumes. Ollas are not recommended for use in clay-based soils as the water will not distribute evenly.  

Types of Ollas 
There are several types, a hand-built clay pot such as the above picture, olla bottles (cylindrical shape), olla drip ball irrigation systems or DIY terracotta pots. 

How to Make Your Own Olla from Terracotta Pots 
This project will only take a few minutes of your time.  You will need the following:  

• 2 terracotta pots   
• Something to cover the hole on the bottom pot (I used a piece of shale) 
• Something to cover the top of the pot (I used a cork from an empty bottle) 
• Silicone (exterior grade)   

Step 1: Cover your work surface with newspaper or cardboard 

Step 2: Use the silicone to attach a flat object to cover the hole 

Step 3: For extra assurance, I filled the bottom of the hole with silicone 

Step 4: Place a bead of silicone around the top of the pot 

Step 5: Place second pot on top

Step 6: Let silicone cure 24-48 hours

Test your olla for leaks by filling with water.  If there are leaks, let dry and add more silicone.  

Now you are ready to use your olla in the garden or in a large pot!   
 
Tips for Using Ollas 

• A saucer can be placed below the olla to encourage water to seep outwards rather than downwards.  
• The olla needs to be buried into the ground BUT you should leave 3- 5 cm (1-2 inches) above ground to prevent dirt or mulch from entering the opening. 
• Space small ollas 60-90 cm (2-3 feet) apart, and large ollas (2 gallon capacity) 90-120 cm  (3-4 feet) apart.  
• Use a stick to check the water level in the olla and add water as necessary.  
  

I used the ollas in my tomato patch. To experiment, I planted some tomatoes with ollas and some without. The ollas provided moisture at ground level and the plants that were near the olla were a little larger than the plants without ollas!

References: 
https://wateruseitwisely.com/olla-irrigation/ 
https://www.acmesand.com/rainwater-harvesting/ollas/  

This article, written by SHS President Nancy Hanson, originally appeared in the May 2020 SHS Newsletter, with an update in the March 2021 newsletter.