Ollas: Irrigate Your Garden With Ancient Tech

Ollas are unglazed clay pots you bury in the garden to water your plants. Learn all about this ancient technology in our complete guide!



Ollas (pronounced “oh yahs”) are an old mode of irrigation that originated in China and North Africa over 4000 years ago. Clay pot irrigation was described in writing then but was most likely used in gardens centuries before that. The basic premise is the water would leach slowly from the clay pot and reach a plant’s roots. 

Today, ollas are all the rage, especially in dry, arid places (like Arizona) where the need for efficient ways to conserve and save water is crucial. Not only do ollas provide root systems with the water they need, but they are also a low-tech water source for plants that’s easy to understand and set up. They address issues of soil surface evaporation and irrigation waste directly!

Before we get into the nitty gritty of what ollas are and how you can use them, I’ll say that we at Epic Gardening recommend you purchase the olla we sell in our online shop. While there are plenty of brands to choose from, these ollas are small enough to adapt to many different pot and raised bed sizes, and they have a really cute happy face on them!

What Are Ollas?

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We already established that olla irrigation is a clay pot irrigation method that uses deep watering to provide moisture to your plants and the surrounding soil. No matter the type of olla, unglazed clay pots are filled with water and buried in the garden to release water throughout the growing season. 

Historically, the term ‘olla’ refers to a clay pot. Everyone from the ancient Greeks to the people of China and Africa used clay pots for storing food, and they had varying symbolic significance. Native Americans in the southwest United States and Mexico employed ollas to keep plants watered during hot summers in the desert. 

And today, ollas are employed all over the world for all of these reasons. They’ve been important to many contemporary gardeners as a gradual and cost-efficient way to water directly at plant roots rather than at the surface level. 

How Do Ollas Work?

While you may already know how these work, let’s discuss the topic in more detail. The olla is buried in a garden or container with the top above the soil. The olla is filled with water, and the unglazed clay container walls allow the water inside to move through the pores of the reservoir into the soil as a slow seepage. 

Suction is created through the soil moisture tension around the pot, which pulls water from the olla faster when the soil is drier. On the flip side, if the soil is exceptionally wet from rain, the water remains within the pot until the soil dries again and water is needed. This means plants don’t go through intense cycles of wet and dry, which protects them through times of drought.

The shape of your olla has an effect, too. Most have a tapered neck that reduces evaporation near the ground’s surface. While a DIY olla may not be as optimally-shaped, it can still work, but you may need to fill it more often.

An olla doesn’t just help you save water which might be subject to evaporation before it can even get to the plant roots you’re watering. It also reduces surface irrigation, which promotes weeds. So you’ll see a boost in the production of your tomatoes, leafy green plants, and overall produce quality, and a reduction of weeds too! 

Best Climates For Ollas

Kevin with ollas
Ollas come in many shapes and sizes.

Ollas are great for arid regions of the world with hot summers and very little rain water. That’s right! If you live in a desert climate, a dry mountain climate, or even a humid hot environment, ollas will work very well in your irrigation system and keep your plants watered even through a drought cycle. 

While these low-rain-water climates are most suited for watering the garden with ollas, you can definitely use them in other climates. Gardeners can use ollas to avoid wasting water or precious time, as they provide a self-watering mechanism to plants that might otherwise receive less water. This is perfect for areas that periodically go through high heat and low rain seasons. It’s also great if you’re about to head on vacation and want a little extra water on hand for plants to access!

The only weather an olla may not be suited to is a consistently cold or frozen region, where it can’t withstand the freeze-thaw cycles that make soil swell and contract. We’ll get into this a little more when we discuss the maintenance of your ollas. 

Plants Most Suited to Olla Irrigation

Some plants are better suited to olla irrigation. Usually, these plants have large fibrous roots, like tomatoes, melons, squash, and chiles like jalapenos. Young trees and more mature trees benefit from olla watering too. 

You may also discover you’re growing the most lovely greens after ollas are introduced into your garden. These heavy feeders require a lot of nutrition and water in their growth process, and providing them with an olla will take care of half of that for you. 

Beans and grains like wheat, especially on a large scale, don’t do as well as the aforementioned crops with ollas because they cover a lot of the soil surface. Therefore, if you’re deciding whether or not to use ollas for these crops, at the very least, provide some supplemental irrigation from hoses if you do.

Finally, some root crops like carrots or parsnips may have a rough time with an olla as their primary irrigation source. This is because the shape of the olla typically widens out as it goes downward, which can cause long, straight root vegetables to bend or curve outward. This won’t make them inedible, but it might make them harder to stack up in the fridge later. For these crops, you need to space them so that the plant is not right up against the olla and instead just outside the widest diameter of your vessel. This prevents you from getting those oddly-shaped root veggies.

Adding Ollas To Your Garden

Using ollas in the garden can reduce water usage by 50-70 percent.

Now that we’ve covered what ollas actually are, let’s discuss how to install them in your garden. Especially for those in arid regions with high heat, much more lush and substantial growth will occur when there’s a switch to gardening with them.   

Olla Size

Start by surveying your garden. How much space are you growing in, and how much water is needed? If you’re growing container plants, the olla in our shop is a perfect size. Larger ollas are great for gardens that have a lot of ground to water and tons of plants that need access to the olla irrigation system. 

Of course, there are options. You can purchase ollas from many different distributors, or you can install DIY ollas made from a basic terra-cotta pot with the drainage hole filled in. Fill with water, cover with a terra cotta saucer, and bury it in the garden. You can even connect two pots together to create a taller vessel!

The basic rule for knowing which olla to choose for your raised bed, in-ground garden, or containers is this. A 1-quart olla provides irrigation to plants in a 1-foot diameter. A 3-quart-sized olla provides water to plants in a 1.5-foot radius. Finally, a large olla that holds about 7 quarts of water provides for plants in a 2-foot radius. 

Where To Place Ollas

Olla water radius
Each olla has a circular radius where water will seep out to.

When you’ve selected your olla size, it’s time to “plant” it in the garden. Whether you’re working in raised beds, in-ground beds, or containers, the process will be the same. Start by digging a hole large enough to place the olla in. Place the olla in the hole, so the top few inches of the neck is exposed above ground. 

Pack the soil around the olla, ensuring there aren’t air holes in the soil. The olla won’t emit moisture into an area that doesn’t have packed soil. Then, space your plants so that they’re in the appropriate radius from the olla, depending on its size. Plant them and fill the olla up, with the water level to almost full. 

Place the lid over top to prevent the entry of runoff and evaporation. You can even fill it with a combination of water-soluble liquid fertilizer and water, although we don’t recommend that often as it can clog the terracotta’s pores. Then let the watering begin!  

Spacing multiple ollas appropriately is important for ensuring that every plant has access to a water source. If you’re working with a long gardening space, you’ll have more room to install more ollas at once. Provide only one olla per smaller single container. You’ll give plants all the water they need when you space small and medium ollas through a raised or in-ground garden at a rate of 2 to 3 feet apart. Large ollas can be spaced 3 to 4 feet apart.

For additional information on developing a placement strategy, watch our video above to see how best to plan out olla spacing!

Refilling Ollas

As your olla sits in the garden, it will water the soil around it, and some will also be removed from the clay pot through evaporation. While the rate of evaporation within the olla is not nearly what it would be on the soil surface, you’ll want to check your olla regularly to ensure it doesn’t need refilling. 

When the clay pot olla has an interior water level of 50% or less, it’s time to replenish the water source. Most of the time, this will occur every five to seven days, but your soil type and weather conditions have an impact on the refilling frequency as well. Once you’ve refilled a few times, you’ll get a sense of when the refilling generally occurs. 

Of course, in summer, you will fill more often than in temperate seasons. Additionally, those in dry Arizona climates would likely be refilling more than those in humid North Carolina. As long as you keep up with it, you’ll notice the difference in your plants from the beginning.     

Olla Maintenance And Troubleshooting

Jacques planting an olla
Jacques is setting an olla in place before backfilling with soil.

Ollas are pretty low maintenance, but there are some issues you might face when you work with them. Here’s some information on how to handle olla maintenance and long-term care!

Cracked Ollas

With anything made of unglazed pottery, there are a few risks. Regular freeze/thaw cycles can cause an olla to crack. Similarly, the roots of trees or shrubs can work their way into the porous terracotta and potentially cause cracks. 

Hairline cracks may not require any repairs at all, but your olla will potentially be weaker and at risk of being cracked by a persistent tree’s root or additional freeze and thaw cycles. For more severe cracks, a water proof epoxy can be used to seal the crack. A large crack in the olla’s base can also be covered with a piece of tile glued in place to stabilize it, although this method is best used on the base; the tile can get in the way of moisture distribution if it’s on the side.

Another method for sealing cracks is to use a silicone putty to seal the crack; this method will fill some of the pores in the unglazed pottery, so this technique is best if done on smaller cracks. It can, however, prevent a smaller crack from becoming much bigger.

Removing Ollas In Winter

Remember who we just talked about freeze/thaw cycles? If you’re in a climate that gets regular freezes and thaws throughout the winter, removing your olla from the ground during those cooler months is one of the best techniques you can implement. Typically, there’ll be quite a bit of rain or snow during those colder seasons, so the olla is not as necessary then. 

Gardening with ollas year-round is an option in warmer climates such as southern California or parts of Arizona or Florida. But if you know you’re in a cold climate, carefully loosen the soil from around the olla. Remove it by lifting it straight out of the hole, and dust off any clinging dirt. Fill the hole with your planting medium, and add mulch on the soil’s surface to help retain moisture and to insulate the soil below. You can then clean your olla and store it until after the final frost.

Cleaning Your Olla

People with hard water may find that their olla begins to get clogged over time as the minerals in your water fill the pores of the unglazed clay. Saving your olla from this fate is doable, however! 

Installing a filter on your water source for your hose water can reduce some of the mineral build-ups, but it won’t prevent all of it. At least once a year, it’s good to remove your olla from the ground or containers and give it a good thorough soak and rinse in distilled water. A bucket works great for this process.

If necessary, you can use a soft-bristled brush like a dish brush to gently scrub any water scale off the surface of the clay. This should remove any loose dirt from the surface as well. Use the same brush to gently scrub the interior of the olla as well to eliminate the whitish buildup from hard water.

This same technique can save your olla if you’ve used it regularly with liquid fertilizers. Over time, particulate matter in the liquid fertilizer can build up, spreading throughout the interior of the olla. This can block the porosity of the terracotta and reduce moisture transfer. Occasionally check to see how well the olla is doing its job of spreading water, and if needed, remove and do a cleaning. Again, distilled water is best for this.

Finally, if your water has high salinity, it will act much like hard water does and eventually plug up the porous surface of the olla. High salinity can also cause problems with plant growth in the soil, so in situations like this, you may want to filter your water or use rainwater in your garden instead.

If your olla has been in a location where a diseased plant was located, you may want to sterilize it. To do so, add a little bleach to the distilled water (but no more than 1 part of bleach to 10 parts of water – it doesn’t take much!) and then place your terracotta in it to soak for a little while. Usually, soaking it for a few hours is enough to sterilize it. Remove the olla from the bleach soak and soak it again for another few hours in plain distilled water to allow any excess bleach to transfer away from the terracotta. It’s now ready for use in the garden again.

Olla Concerns

In hot climates, particularly dry and drought-stricken areas, the summer may cause you to fill your olla much more frequently. This is to be expected, as water evaporates out of the growing medium much more regularly during those times. This isn’t the end of the world, but you will need to keep a regular eye on the water inside to ensure you’re not running low.

Another common issue is that ollas don’t always work with other garden techniques. People who grid off their gardens using square-foot gardening methods may find that an olla won’t reach all parts of their grid sufficiently. With olla irrigation, the best planting location is where the roots of the plant will easily reach the pottery or where they’ll be within range of the transfer of water through the soil. This doesn’t eliminate the possibility of square-foot gardening with ollas, but you will have to plan accordingly.

Finally, seed starting with an olla is problematic. Remember, seeds need consistently moist conditions, and they’re usually up near the surface of your growing medium – and the level of water in the olla may be below that. It’s much more efficient with seed starting to irrigate your seeds and very young seedlings to get them started off right. You can gradually wean them off the supplemental watering as they get larger.

Frequently Asked Questions

DIY olla
You can make a DIY olla out of terracotta pots, but it may not be as effective.

Q: What do ollas do?

A: They provide irrigation to plants via osmosis, leaching water from a buried unglazed clay pot toward roots. 

Q: Does olla watering work?

A: It does! Those in appropriate climates irrigating certain plants will notice a boost in production. An olla may not be necessary if you’re in a location that typically gets lots of rain throughout the year, but those in dry climates will find them beneficial.

Q: What plants are ollas good for?

A: They’re particularly suited to cucurbits, tomatoes, and leafy greens. They aren’t as suited to grains and legumes.  

Q: How long does water last in an olla?

A: Usually anywhere from a few days to a week, depending on weather conditions. 

Q: Do ollas crack in winter?

A: They can! That’s why it’s recommended you dig them up and move them indoors for winter. 

Q: How many ollas do I need?

A: It depends on your garden space and how many plants you’re growing. Ollas have a limited radius that they can water, and more garden space will require more olla coverage.

Q: How big should an olla be?

A: See the question above. Larger ones have a wider watering radius. 

Q: How much area can an olla water?

A: The radius depends on how big the olla is. 

Q: Can you add liquid fertilizer to an olla?

A: While you can do so, liquid fertilizers are typically thick and filled with particulate matter. That particulate can build up on the inside of your olla and clog the pores of the terracotta, reducing your olla’s ability to water consistently. The largest particulates may never pass through the terracotta and into your garden where they could do the most good. As a result, we prefer to recommend watering and fertilizing separately.

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