I learned about olla gardening last year when an irrigation system wasn’t an option and I needed a long-term alternative to watering with the hose (which, in my garden, ends up being either a death sentence for plants or a waste of water). It turns out that a lot of other people have also just recently been learning about gardening with olla pots, even though this effortless, resource-saving watering technique has been in use for more than 4,000 years.
Their resurgence in popularity in the United States comes at a time when water conservation and convenience are top priorities in our gardens. Unfortunately, these are two things that don’t always go hand-in-hand. It’s all too easy to waste water with automatic irrigation systems, but the more time we’re forced to spend tweaking them, the less convenient they become.
An olla (pronounced “oy-yah,” known as an olla pot or olla jar) watering system is nothing more than an unglazed clay pot that is buried under the soil, preferably near a thirsty plant. The clay that ollas are made of is porous enough to allow water to slowly move from the jar into the dry soil around it. The roots of nearby plants grow toward the olla, and they eventually form a dense mat around it, drawing water as needed from the surface of the clay.
There are many shapes and sizes available, but they’re often shaped somewhat like bottles with wide bottoms (the wider the better, for the most efficient watering radius) and long, tapered necks. Their tops are left slightly above the soil line when ollas are buried, allowing for easy refills. A cap or rock over the top helps to keep water from evaporating. The neck and lip can be glazed to prevent water from wicking up and above the soil line.
A modern version of this ancient watering system is also available. One company in Tucson, Cutting Edge Ceramics, has a patent pending on olla balls that are attached to irrigation lines, allowing many smaller ollas to remain filled from a single water source. The more traditional olla pots drop water use by an astounding 50-70 percent, and users of the olla ball system are reporting even deeper water savings.
Ollas reduce water waste by delivering water directly to roots below the soil surface, eliminating water loss from evaporation and runoff. A plant growing on olla irrigation is able to draw just the right amount of water whenever it wants, rather than receiving a set amount of water on a schedule that often doesn’t match its needs. Water needs can vary by the plant, the day, and the season, so applying the perfect amount of water is nearly impossible. Because the water supply is constant and steady, ollas keep fruits like tomatoes and peppers from getting disfigurations, cracking, or splitting, all of which often occur when they’re watered erratically or allowed to get too dry.
Another benefit of this subsurface water delivery system is that it helps reduce weeds. Seeds have a hard time germinating with no water at the soil surface. Those that do germinate have a hard time getting their roots deep enough to reach the olla. This means that when you do want seedlings to find your olla, you’ll need to help them along with regular watering until their roots reach the subsurface moisture, which extends out about the same distance as the olla’s radius.
Plants can be fed through an olla by adding water-soluble fertilizers. Compost tea can also be used, or graywater, but an olla will only work as long as water can pass through its pores, so make sure that anything you add to the olla is extremely well-filtered with no solid particulates floating around. It’s also important to keep your olla pot full rather than allowing the water level to get too low. Salts and other minerals can build up on the surfaces of the clay as the water line slowly drops, so it’s best to keep the water level above 50 percent as often as possible. You’ll get many more seasons of use by keeping those precious pores unclogged.
Once the growing season is over, dig up the olla along with all of the tired veggies. Scrape off any roots that are attached to the clay and give the jar a good scrub before storing it or planting it with the new season’s crops. Store it over the winter if you live in an area where the ground freezes.
There is one downside to working with ollas; they’re made of clay that is fired at low temperatures and, while the result is very porous, it’s also fairly brittle, and will naturally deteriorate with repeated use. You have to be extra careful when moving, storing, or digging around your olla jar to prevent cracking or breaking the clay. After about five years you’ll probably need to purchase or make a new jar, even if you’ve taken excellent care of it.
Since fast-growing, woody roots can easily crush an olla, you have to pay attention to what’s nearby before deciding where to plant it. If a thirsty tree or shrub is in the vicinity, it may be best to limit your olla use to raised beds or large planters. That said, savvy gardeners have been known to make inexpensive ollas to help get trees or shrubs established, knowing that they won’t be able to dig up the ollas to use them again.
Growing interest means that it shouldn’t be too hard to find ollas for sale. Ask at your local nursery to see if they carry ollas, or if they can order some for you. Many garden centers and large retailers are also beginning to regularly stock ollas. Detailed step-by-step instructions for making several different types of ollas are posted online for those who like to DIY. Check out the chapter on olla pots in David Bainbridge’s new book, Gardening with Less Water (Storey 2015). And as you’re saving yourself all kinds of water with your new ollas, make sure to stop and muse over how our favored irrigation methods have come full circle. ✜
Those at the highest elevations of Baja Arizona (above 4,500 feet) can continue to plant onion sets through the beginning of February, and it may warm up enough by mid-February to begin planting horseradish, kale, and spring peas.
If you live between 3,000 and 4,500 feet there’s not much going on in January (though dry onion sets can still be set out through the winter months and into mid-March), but the garden really gets going in February. Endive, horseradish, and kale can be planted early in the month, and pepper seeds can be started, too. Around mid-February you can plant asparagus, cabbage seed, Swiss chard, garlic, kohlrabi, leeks, head lettuce, mustard, green onion, parsley, spring peas, pepper plants, and spinach.
It may still be cool enough between 2,000 and 3,000 feet to get some last-minute winter crops in the ground. Plant Chinese cabbage, collard greens, leeks, head lettuce, parsley, and parsnip before mid-January. Cabbage, cauliflower, endive, horseradish, kohlrabi, mustard, and green onion can be planted by the beginning of February if temperatures remain cool. Kale and onion sets can be planted by mid-February. You can also plant asparagus, beets, carrots, Swiss chard, leaf lettuce, radish, rhubarb, rutabaga, spinach, and turnips through the end of February. Meanwhile, tomato seeds can be started from mid-January to mid-February, spring peas can be started in early February, and pepper seeds and potatoes can be started by around Valentine’s Day.
Gardeners between 1,000 and 2,000 feet have time to plant green onions, dry onion sets, rutabaga, spinach, and turnip by early February. By the end of February plant asparagus, carrots, leaf lettuce, Swiss chard, and tomato and pepper seeds. Beet and radish can be planted through the end of February and beyond. Early in February eggplant, potatoes, and summer squash can be started if temperatures are warm enough. By mid-February you should be able to plant bush beans, lima beans, cantaloupe, sweet corn, muskmelon, tomato starts, and watermelon.
The very lowest elevations of Baja Arizona (below 1,000 feet) are still able to plant beets, cantaloupe, cucumber, muskmelon, radish, summer squash, and watermelon through the end of February. Potatoes should be planted by mid-February, and asparagus, rutabaga, spinach, and turnip can be planted until around the end of January. Green onion, dry onion sets, parsley, pepper seed, and tomato seed are usually best if planted by around mid-January. Tomato plants can be started as early as the beginning of January, and by the middle of that month you should be able to plant eggplant, and spring peas. Around Feb. 1 you can begin planting bush beans, lima beans, and pepper plants. Look to plant sweet corn as early as mid-February if temperatures are warm enough. ✜
Amy Belk is a garden writer and photographer, a certified arborist, and a certified nursery professional who has been learning from her garden for 15 years. She and her husband homestead on a little piece of the desert in the heart of Tucson.