Olla Irrigation for a Market Garden

An olla buried in the garden.Image fromhttp://www.apartmenttherapy.com

An olla buried in the garden.
Image from

It’s January. And it’s cold. And I’m glad… mostly. I’m not a fan of cold weather, but I’m hoping a cold, snowy Michigan winter means a drought-free Michigan summer. Cold weather also means I have some time to create plans for making our 2013 season even more successful than 2012. I’ve been doing research on irrigation systems for our 2013 garden and I’d like to share the results of this research with you this week.

A major component of my irrigation plan is hugelkultur. If you’ve been following this blog than I’m sure you’re sick of me throwing that term around. If you haven’t been following my German-term throwing antics, then I’ll just let you know briefly that hugelkultur (“mound culture”) is a gardening method that has been used in Eastern Europe for centuries and is essentially a sheet-composting method that involves burying woody debris (logs, branches, sticks) and other organic matter under a mound of earth to add nutrients to the soil and retain moisture. For more on my adventures in installing hugelkultur beds, click here.

I sincerely hope that hugelkultur will reduce our irrigation needs but I’m not quite optimistic enough to trust that it will eliminate the need to water. So I’ve set out to develop a sustainable irrigation system that minimizes labor, reduces costs, avoids overhead watering, and stores extra water while maintaining aesthetics appropriate for our suburban setting. I want the system to minimize reliance on city water. And I’d like fries with that too, please.

Ollas and How They Work

The next major component of the plan is the use of ollas (pronounced oy-yah). According to Lori at Dripping Springs Ollas, “an OLLA is an unglazed clay pot fired at a low temperature. This allows the pot to remain porous. The OLLA is buried in the ground with neck exposed and periodically filled with water. The water seeps into the soil at a rate that provides adjacent plants with a constant water source at the roots.” The use of Ollas is an ancient practice. This system has been used in China, Pakistan, India, Iran, Mexico and Brazil. Irrigation with ollas is said to be up to 10 times more efficient than conventional surface watering. Here’s why…

According to Curtis W. Smith (NMSU Extension Horticulture Specialist) “When ollas are used properly, plant roots will proliferate around the moist clay jar, intercepting water before it can move through the soil by capillary action. This water intercepted by plant roots will then be used in the plant transpiration stream. This results in almost 100% of applied irrigation water being absorbed by the plants.”

Benefits of Ollas

Besides simply being an efficient way to water plants, ollas provide the benefit of avoiding overheard watering. Overhead watering can promote the growth of mildew and fungus on plants, especially tomatoes and cucurbits (cucumbers, zucchini, squash, etc.). Because the moisture is applied below the surface (and in many cases directly to the roots) the surface of the garden remains dry. The benefit to a dry surface is that weed seeds that make it to your garden bed are less likely to germinate. And the slow/on-demand wicking of water into the bed means that erosion of soil and nutrients is a non-issue. And lastly ollas can be a more sustainable method of watering than the conventional hose-and-sprinkler system because they don’t rely on water pressure or a city water hookup to ‘operate’.

Challenges of Olla Irrigation

Sounds like a pretty sweet solution, doesn’t it? But there are some challenges. The primary hurdle is cost – Ollas can cost $20-$30 each for a 1.5 or 2 gallon olla. If you need several ollas per bed, that can get to be pretty pricey. Also, I’ve not seen this concern voiced in any of my research, but personally I worry that a buried olla will take up soil space needed by roots in some cases. And lastly, there’s the challenge of how to fill them efficiently. This is probably not a universal concern since those of you with family-sized kitchen gardens can easily spend a minute or two filling each olla with a hose. But because I’m looking at using lots of ollas (nearly 200) and I want to avoid using city water, figuring out how to efficiently fill these puppies is a challenge for me.

Rain Rules and Olla Inventories

Allow me to quantify my challenge. The generally accepted rule is that a garden needs 2” of rain per week. According to the USGS, 1″ of rain per acre = 27,154 gallons. That means 2” of rain is equal to 54,308 gallons.

One acre is equal to 43,560 square feet, which means that 2”of rain is equal to 1.25 gallons per 1 square foot. So to get the generally recommended amount of water per square foot, each of our large garden beds (48 square feet) need 60 (59.84) gallons of water per week. These ratios seem to be supported by ratios listed at this site as well, which says that for every 1” of rain on 1 sqf, you will receive .623 gallons of water. Thus, a 2” rain should provide 1.25 (1.246) gallons of water in the same square foot.

Friends, I’ve never measured how much water I use, but that just seems like soooo much water to me! Can that be right?

For some hands-on perspective on how much water/how many ollas I should be using, I turned to Lori from Dripping Springs Ollas. She recommended that I use 3-4 two-gallon ollas per raised bed and fill them two or three times a week. (Raised beds here at Arcadia Farms are 4 feet wide x 12 feet long x 1 foot deep.) Four two-gallon ollas filled three times a week comes out to 24 gallons of water per week, or about half of the 2 inch “rule.” It’s a rule breaker, but that seems much more realistic to me!

At any rate, to achieve the recommended ratios of rain, each bed would need around 8 one-gallon ollas filled daily. If it takes 1 minute to fill each jug, that’s a lot of labor time (like 22+ hours a week)! I’m hoping to reduce labor, not increase it! Though the alternatives below wouldn’t reduce the amount of time, they would at least compress the time into fewer “watering days” as opposed to spending 3 hours every day.

  •  8 one-gallon ollas filled every-other day: Once in the morning and once in the afternoon
  • 15 one-gallon ollas, filled once in the morning and once in the afternoon, twice per week

Developing a system that can fill 8 ollas at a time would dramatically reduce labor by allowing other tasks (i.e., weeding) to be done at the same time as watering.

Clay olla.Image from http://www.apartmenttherapy.com/olla-gardening-the-original-dr-78565

Clay olla.
Image from http://www.apartmenttherapy.com/olla-gardening-the-original-dr-78565

Minimizing Challenges and Maximizing Benefits

In my research I found a nifty way to reduce the cost of olla irrigation: Re-use gallon milk jugs. By placing pin holes in the jugs you get the same slow-drip, below the surface benefits although the ‘wick away as needed’ benefit is probably lost. With buried milk jugs, the surface stays dry (weed control) and roots get a slow, steady source of moisture. This approach reduces my costs from around $3,800 to $0. Eventually I’d like to change over to using clay ollas exclusively. Starting with milk jugs buys me time to incorporate the real deal into our garden on a gradual basis.

I did a little experiment using a milk jug with four pinholes in the bottom. I placed the jug on a thickly folded beach towel. With the cap on, there was no drippage to speak of at all. With the cap off, there was a slow drip that took approximately 5 hours to empty the container. Sounds good to me! To address this cap-off need, I plan to cut a half- or quarter-inch hole in the cap and line it with mesh from the inside. I’m hoping this will allow for drainage without allowing debris and small animals to climb inside the jug.

All the same, I’m still a bit concerned that burying milk jugs will eat up soil space needed by my plants. And I think the impact of buried ollas on soil space will vary depending on the plant. A tomato plant taking up 2 square feet probably won’t mind a buried olla or two as much as a SQF of carrots. I plan to experiment with both buried milk-jug ollas and above ground versions, using above-ground versions for root vegetables.. To keep the above ground ollas from blowing away, I plan to add a layer of gravel to the bottom. It will also be interesting to see if exposure to sunlight promotes the growth of algae in the containers or if they will drain quickly enough to avoid that kind of build up.

And don’t forget that half of our raised beds are hugelkultur beds. If these hugels retain and distribute water as well as they are supposed to, it should reduce our watering needs. I’ve tried to research how often other growers water their hugels. Most of the claims I’ve found are that they have never been watered or watered just once a season. As I mentioned at the beginning of this post, I’m not going to bet the farm (ha!) on a ‘no-water’ season, so for purposes of this irrigation plan I will assume that the hugelkultur beds need only 1 inch of rain per week. I secretly hope they’ll only need .5 inch (Shh! Don’t tell!).

That assumption (1 inch of rain per hugel per week) should reduce my watering time by 25%.

Automated Olla Filling

That plan leaves yet one challenge: How to fill the ollas. I’m making plans for a rain capturing system that I’ll share about in an upcoming post. I think I could use gravity or a small solar-powered pump with a hose to move water from our rain storage to the ollas. In addition, I’d really like to set up a system that fills 8 (or at least multiple) ollas at once to save on labor.

Our rain catching system will mainly consist of a small shed (don’t know the size yet) with a metal roof that captures rain with gutters and stores it in a 250 gallon tank. That’s a nice amount of rain water, but if each bed really needs 60 gallons a week, 250 gallons isn’t going to go very far. (As in, it won’t even come close to covering one week.)

If anyone has ideas about how to 1) automate filling ollas, 2) automate filling more than one olla at a time or 3) store more than 250 gallons of water without a giant investment (think: less than $400) I’m all ears!


Interested in using ollas for watering your garden? Here are some resources I found helpful.

http://drippingspringsollas.com/ <– Start here




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