Written by: Di Graski, Colorado Master Gardener
My husband and I first learned about olla pots during a garden tour in Colorado Springs several years ago: an urban farmer used olla pots in her tomato planter to deliver water steadily to her massive, productive plants. We vowed to try this irrigation technique, and we are so glad we did! We’d like to share our experiences over the past three growing seasons with our fellow Pueblo gardeners.
What is an “olla pot”?
“Olla” (pronounced OY-ya) is the Spanish word for “pot” (so saying “olla pot” might be redundant?). In a horticultural context, “olla pot” means any unglazed clay vessel that is buried in garden soil and then filled with water to irrigate plants. Clay is porous, so the water inside the olla pot will seep through the walls of the pot until equilibrium with the surrounding soil is achieved (yay, osmosis!). Essentially, olla pots provide your plants with an underground reservoir of water they can tap. Not too much water and, as long as the olla pot is replenished, not too little. As Goldilocks would say, “Just right.”
Where can you find olla pots?
You can spend a bundle on fancy-pants olla pots from a variety of online vendors – just search the internet for “olla pot” – but you probably already own most of the materials you need to make your own:
- Unglazed clay pots.
- Small flat rocks, or tiles, or what-have-you, just a smidge larger than the diameter of the drain hole in your clay pots.
- Ideally, food-safe caulk, but any waterproof caulk will do. Or maybe you have an aquarium-repair kit laying around?
We chose to construct our olla pots by wedding two seven-inch clay pots, meaning we plugged one drain hole, then glued the two pots’ rims together, leaving the top pot’s drain hole to serve as our fill hole. Others choose to use a single clay pot, so they simply plug the drain hole and then use a waterproof cover to retard evaporation and to prevent soil, mosquito larvae, debris – and, as Master Gardener Bob Frederick discovered years ago, toads – from taking up residence inside the pot. Upside-down plastic planter saucers are perfect olla-pot covers.
What are the advantages of using olla pots?
Each of our olla pots can deliver about a gallon of water to the roots of our plants: one seven-inch-diameter terra cotta pot holds about a half gallon of water, and our olla pots are comprised of a pair of pots.
Olla pots and raised beds are a match made in Gardener Heaven! Those of us who use raised beds know that keeping our garden soil moist during Pueblo County’s hot, dry, often windy summer days can be a real challenge. Mulching helps, but many days simply require morning and evening irrigation . . . and sometimes not even that is enough. Especially for big, thirsty vegetable plants like tomatoes and squash, whose fruits suffer blossom end rot when water is not steadily available, olla pots are an amazingly effective irrigation technique.
During the growing season, I fill each of our olla pots every morning using a watering can with no sprinkler cap on the spout. When we’re lucky, we have an ample supply of rain water in our barrels to supply the water for our olla pots. Other folks might choose to use a garden hose to refill their olla pots. Some have even rigged drip irrigation systems to replenish their olla pots: our neighbors with the Riley County, Kansas, Extension Office show such a system in their article about olla pots. See Eyestone.
2025 will be our olla pots’ fourth growing season, so not only are they effective, they are durable.
Any disadvantages?
We cannot recommend olla pots as an irrigation method during the germination of seeds sown directly in garden soil, because the area of moist soil surrounding an olla pot is limited: research published in 2017 reported that 20 centimeters (roughly seven inches) was the maximum reach. See Nickel and Brischke, May 2021. For the same reason, shallow-rooted vegetables like spinach and lettuce would not be a good match for olla-pot irrigation.
Olla pots are not a sufficient irrigation method for new transplants, either: your young plants will need supplemental water for a few weeks, while their roots detect the olla pot as a water source and then grow to it.
Olla pots do take some space. And as our plants mature, gaining access to the olla pots’ fill holes can get tricky: last year, my husband rigged a tube and funnel system that allowed me to fill an olla pot where an indeterminate tomato plant’s branches blocked my watering can.
Maintenance of olla pots
After our growing season ends – and definitely before any hard freeze – I remove the olla pots from our raised beds, empty any water left in them, set them in the sunshine until they are completely dry, brush off any soil or roots still attached, and then store them in our garden shed through the winter.
In May, when it is almost time to transplant our seedlings to their summer homes, I pull the olla pots out of the garden shed and give them a vigorous brush to remove any debris and minerals. A good soaking with diluted bleach would be a good preventive measure, also.
Want to learn more?
Gregg Eyestone, “Olla Irrigation,” K-State University Research and Extension – Riley County, https://www.riley.k-state.edu › docs › lawnandgardenandother › olla.pdf .
Carrie Knutson, “Olla Watering,” North Dakota State University Extension – Grand Forks County (August 2023), https://www.ag.ndsu.edu/news/columns/dakota-gardener/dakota-gardener-olla-watering .
Amy Nickel and Andrew Brischke, “Irrigating with Ollas,” University of Arizona Cooperative Extension (May 2021), https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1911-2021.pdf .
Regarding the connection between irregular irrigation and blossom end rot, please see Plant Talk Colorado™ #1826, “Water Related Problems in the Vegetable Garden,” https://planttalk.colostate.edu/topics/vegetables/1826-water-related-problems-vegetable-gardens/ .
Lots of “how to make an olla pot” videos are available online.