Master Gardener Monthly: Why Your Garden Needs a 2,000-year-old Water System

By Julie Knapp

When most people think of watering in a low-desert landscape, thoughts go to drip lines or flood irrigation. Both of these require continual access to water, which limits where and how much you can plant.

Unless you live in older city sections or you are near farmlands, you probably don’t have access to flood irrigation. This type of watering is only successful with lawns and orchards, anyway. If you want to grow a vegetable garden or plant flowers and groundcover other than lawns, you have to seek other means.

A successful choice for the Southwest low desert is an olla (pronounced OY-yah). Irrigation ollas can be traced historically 2,000 years ago in China, but no one really knows when the first olla was used. When you don’t have a drip system in a planting area, an olla can save the day.

An olla is simply an unglazed clay pot with a neck or hole at the top to add water. Because the pot is unglazed, water will seep through the clay underground. It was a great way for indigenous people in China, South America, Africa and North America to irrigate crops. The pots were buried in the ground next to the plants with only the small opening above ground. The plant roots reached out to the water seeping from the olla. This system allowed people to haul water to the crops less frequently and to use water more efficiently.

Horticulturists in Texas and New Mexico have tested ollas and found that crops and urban gardens flourish because the plants take water whenever they want and only the amount they need. Unlike irrigation that has dry times in between watering, the plants have a constant flow that allows them to continue growth without stress. The results have been phenomenal with healthier and more productive plants, less evaporation and water use, and lower weed growth. What more could a grower ask for?

An additional advantage is that you aren’t reliant upon where your irrigation and drip lines flow. You can grow plants anywhere you would like. Simply bury the ollas in the ground next to your plants, refill it when its water level is low, and let your plants thrive.

You can purchase ollas for $20.00 to $50.00, or make your own for about $3.00.

Automated ollas

As I added a raised bed that was not on my drip line, I wanted to automate the ollas so that I didn’t have to fill each one individually. To build it, place a large 5-gallon bucket on the raised bed edge a bit higher than the soil level. If you don’t have a wide edge, place a second bucket upside down as a platform for the bucket reservoir. Drill a hole near the base of the bucket and seal a half-inch drip tubing in the hole, then run the line down the center of the bed. Attach a spaghetti line (1/4-inch lines) and an emitter to each olla, then insert the other end into your half-inch tubing.

When making your own ollas, place the emitter at the end of the line inside each one and seal the spaghetti line at the top hole with silicone so it will stay secure. You can also buy premade systems online.

Simply fill the bucket with water and it will flow to each olla. Since the ollas are sealed, the water won’t flow out. It is a simple gravity-fed system that has been used for centuries. It’s also how rainwater catchment systems work.

Whichever olla system you choose, you will cut back on watering frequency, save more water than a drip system, and create a much healthier environment for your plants.

How to Make an olla

You will need:

  • 2 identical 6-inch unglazed terra cotta pots (for small planting pots, use two 4-inch pots)
  • 1 4-inch terra cotta base plate (you will use it as the lid, but some people simply use a large flat rock)
  • 1 large marble or broken tile piece (any smooth non-toxic, non-porous item to plug the hole in the bottom of one of the pots)
  • Gorilla Glue
  • Waterproof caulking silicone adhesive
  • Caulking gun

To make the olla

  1. Caulk the marble into the bottom hole. I use those big shooter marbles for the 6-inch olla. Make sure that it is sealed both on the inside and the outside of the pot. It won’t be pretty, but it will be below ground.
  2. Wet the lip of one of the pots, then apply Gorilla Glue. Turn the other upside down and press it onto the top of the glued pot to adhere the two together. Place several heavy books on top of the pots and let the glue dry for a few hours.
  3. Now caulk the outside seam with silicone and run your finger lightly around the edges to ensure a tight seal. (Gorilla Glue is the tightest connection but it tends to create small porous bubbles. The caulk will fill that in.) Then, put the books on top of the pots again so the seal can cure overnight.
  4. The next day, fill the olla with water to test the seal. If it still leaks, touch up the seal around the sides with caulk again. Make sure that the plugged hole in the bottom is sealed properly.

Julie Knapp is a Maricopa County Master Gardener and Certified Agriscape Designer. She helps people combine their ornamental landscaping with edible plants so that the two blend aesthetically. Julie is a writer, a blogger and an instructor at Scottsdale Community College, where she has designed a future Native American demonstration garden.

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