2016 Silver Nautilus Book Award Winner for Green Living & Sustainability Are you facing drought or water shortages? Gardening with Less Water offers simple, inexpensive, low-tech techniques for watering your garden much more efficiently — using up to 90 percent less water for the same results. With illustrated step-by-step instructions, David Bainbridge shows you how to install buried clay pots and pipes, wicking systems, and other porous containers that deliver water directly to a plant’s roots with little to no evaporation. These systems are available at hardware stores and garden centers; are easy to set up and use; and work for garden beds, container gardens, and trees.
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About the Author
David A. Bainbridge is professor emeritus of ecology and agroecology at Alliant International University in San Diego, California. He is the author or co-author of many books, including The Straw Bale House (Chelsea Green, 1994), A Guide for Desert and Dryland Restoration (Island Press, 2007), and Passive Solar Architecture (Chelsea Green, 2011). He lives in San Diego and has been researching dryland restoration and irrigation since 1981.
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Buried Clay Pots
Buried clay pot (also called pitcher or olla ) irrigation is one of the most efficient systems known, thought to have originated in China thousands of years ago. Filled with water, a buried, unglazed, porous clay pot provides controlled irrigation by capillary flow to plants planted near it.
They come in various shapes and forms: round pots with narrow necks, cylinders, or standard terracotta nursery pots. Because the rate at which water seeps through the pot wall is determined partly by how much water the plant is drawing from the soil, this system is up to ten times more efficient than conventional surface irrigation. Clay pots can be used without pressurized or filtered water and can be made with locally available materials and skills almost anywhere in the world. They are much less likely to be damaged by animals or clogged than drip systems.
I was introduced to clay pot irrigation through a 2,000-year-old Chinese agricultural extension book by Fan Shengzhi, a skilled agronomist and scientist who prepared his book at the behest of the Emperor to help farmers with limited resources. After reading excerpts from his book, I headed out to the garden at the University of California, Riverside, to install some clay pots. Sure enough, they worked — and worked well — with very little water. In a subsequent test in the California desert, I found that all the trees on buried clay pots were alive and healthy after eight months, while all of the trees receiving the same amount of water with conventional basin irrigation had died.
The following spring I started exploring the use of buried clay pots for growing vegetables. I found that melons and squash grew very well and had minimal weeds, despite an appalling level of weed seeds in the university community garden beds. I also grew some Hopi corn (Zea mays) in my shaded back yard with only one-tenth the conventional water use for corn in California.
Meanwhile, I learned that buried clay pot irrigation was still being used on a limited basis in the drylands of India, Pakistan, Iran, the Middle East, and Latin America. The yield of melons grown this way in India, for example, was almost 20 times higher per gallon of water than flood irrigation in California. (I also met a Mexican farmer who put his son through college with clay-pot irrigated melons!) In Ethiopia's semiarid northeast, tomato production was 50 percent higher than with furrow irrigation. In another study, buried clay pots allowed farmers to grow two crops of corn a year, enabling a family to meet their corn needs with only one-tenth of an acre.
Buried clay pot irrigation has been used successfully for a wide range of perennial plants, including citrus, fruit, and nut trees, from pistachio groves in Iran to dry orchards in India to forests in Pakistan. Many of my desert restoration projects in California have been successful with this technique too.
The consistent water supply of buried clay pots improves germination, increases crop growth, speeds maturity, reduces diseases, and increases yields, even in places with very high temperatures, low humidity, and desiccating winds. They can also be effective in sandy or gravelly soils that drain very quickly and with salty or alkaline water or soil. Finally, both water and soil amendments can be placed more specifically to benefit crops rather than spread over an entire plot, resulting in fewer weeds and less fertilizer use. In one trial, the weed weight was only 200 pounds per acre with buried clay pots, as opposed to a gigantic 8.5 tons per acre with flood irrigation.
The size of the buried clay pot, the porosity of the clay (a factor of clay mix and firing temperature), pot wall thickness, water quality, and the water demand of the plants all influence how often you will have to refill the pot, but larger ones can afford you a week or more between watering. This makes this technique a good choice for the suburban or urban gardener who may be able to work in the garden only on weekends.
You can choose to keep your pots filled or to fill them periodically. For our desert work, they would often be completely dry when we returned after two or three weeks — but the trees and shrubs were still alive. In the garden or container, some plants seem to like the added oxygen they get when the pot is nearly empty. This can be especially helpful in fully glazed or plastic containers that don't breathe. Other plants prefer the pots to provide more consistent water, perhaps with a continuous feed line or refilling when they fall to half full. Watch your plants and see what they like best.
Specially manufactured irrigation ollas are now being made and sold in the United States and Australia. Many unglazed pots made in Mexico will work well, and similar pots can be found or made around the world.
Buried clay pots have great potential to aid tree establishment and environmental restoration projects. During tests in the very hot and dry low desert of California, plant survival with buried clay pots often ranged from 78 to 100 percent when all the plants on traditional basin or surface irrigation systems (including drip) died.
Install the pot as in the garden and refill as possible. If you use a rubber stopper, you can pull it out after a year and water deeper into the soil. Pots can usually be pulled after two to three years.
Preparing Clay Pots
Clay pots must be porous, not glazed, and free of wax, paint, or other impervious coatings. They can be tested by spraying them with water and making sure that the surface becomes damp immediately, or by placing them in a bucket of water and making sure the water wets them fully. I use standard red terra-cotta clay pots because they are available in a wide range of sizes and can be found anywhere. Half-gallon to one-gallon pots are convenient, but smaller and larger pots can be used as well. I have found that the 8-inch diameter, 10-inch-tall pots are a convenient size. The bases that are sold with these pots make excellent lids as well.
terra-cotta pot and base
rubber stopper, size 5 for a typical 8-inch pot (see Appendix for a chart of stopper sizes)
(optional) drill with ceramic bit
1. Seal the hole in the bottom of the pot with a rubber stopper. For a shrub or fast-growing plant, put the stopper in from the top so you can pull it out later to encourage deeper root growth. For annual plants, put the stopper in from the bottom so you don't have to worry about it being dislodged.
2. Once the pots are sealed, you can compare porosity by filling them and either measuring the drop in water level or weighing them repeatedly for a couple of days with a good scale — my kitchen scale is accurate enough. Most terracotta pots are very consistent, but occasionally you will find some that are over-fired and impervious in some areas. These areas often appear as an irregular lighter blotch on the clay. After a while, you can recognize this and leave those pots on the nursery shelf.
3. Rest the pot base on top of the pot to create a lid. You can simply lift the lids to fill your pots by hand, but if you want them to collect rainwater, you can drill a small drain hole with a ceramic or glass cutting bit.
4. If you'd like, paint the rims and lids of clay pots with non-toxic paint to reduce evaporation and make them easier to see in the field.
Alternative Methods. To seal the hole, you can also use silicone caulk, epoxy, hot melt glue, or polyurethane glue. Put masking tape on one side of the hole and fill the hole from the other side with the glue or other material.
Pie tins or ceramic plates from thrift stores make good lids if you don't have pot bases. The lid should fit snugly over the top of the pot. For narrow-necked pots, a stone, tile, or small cup will work as a lid.
Handmade Clay Pots
Clay pots are handmade for irrigation in many parts of the world. The clay mix and firing temperature can be adjusted for ideal porosity. Potters are likely to know how to manage grog (broken and crushed pieces of pottery), clay, sand, and other additives to adjust porosity. Increasing the amount of grog in the terra-cotta will increase porosity. Wall thickness, type of clay, and many other factors may affect porosity as well, so test-fire some samples before starting major production.
Firing temperatures can be adjusted to provide suitable porosity and good durability. Do not fire the clay above 1832°F (1000°C), or the porosity may be reduced. On the other hand, if the pots are too low-fired the clay may break up in very saline or alkaline soil as a result of chemical reactions. Permeable pots can also be made of other materials, including concrete, by adjusting the percentage of fine aggregate and sand.
The best shape for a pot depends on its use. A 1- or 2-gallon pot is a convenient size, but pots of 4 or 5 gallons can be used for trees. An olla with a narrow neck and a small hole is easier to cover and plant around, but a pot with a wider top is easier to fill and can catch more rain. A handle makes it easier to lift the lid. For watering plants grown in containers, a slender pot with a taller neck is easier to fit in the container. You can glaze or paint the rim of a pot to increase durability, improve visibility (reducing damage), and just to add some color or character.
Using Double Clay Pots for Container Plants
Double clay pots work well for landscaping and kitchen gardens and are excellent for propagating cuttings in the nursery or field. I have used double clay pots for a wide range of herbs, flowers, and shrubs. They are helpful for plants such as roses that demand considerable moisture but are sensitive to mold and fungus if the leaves are wetted. Indoors, clay pots in containers can reduce problems of water-logging and rapid drying and make damage to floors and carpets less likely.
Try it yourself with a double-clay-pot herb garden. Use an 18- to 24-inch clay pot with an 8-inch watering pot in the center.
1. Seal the hole of the smaller pot and place a screen over the hole in the bottom of the larger outer pot.
2. Place pea-sized gravel or coarse sand in the bottom of the outer pot.
3. Fill the outer pot with planting mix to within about 6 inches of the surface. Make a hole in the soil and place the smaller pot inside the larger one (you can offset it to one side of the container to allow easy access for refilling) so that the top edge of the small pot will be slightly above the rim of the larger pot. Put the lid on to keep soil out, and fill in around the pot.
4. Water the mix and fill the inner pot with water. Let sit overnight.
5. Using a trowel, make planting holes near the outer pot rim, and place the plants, cuttings, or seeds in the moist soil. Leave a space between plants on one side to make it easier to lift the lid and refill the pot with water.
6. Sprinkle the plants or seeds with a watering can to reduce shock and add a bit more moisture to the surface soil. Keep the inner pot filled with water.
Clay pots can also be used to improve soil aeration in glazed, impermeable containers. These containers can cause problems for many species because of lack of oxygen for the roots. An inverted unglazed clay pot can be set in the center of the container to provide oxygen to the soil mix.
Garden with Clay Pots
Most plants are very compatible with clay pot irrigation. Fast-growing water hogs such as squash vines will need big pots or more frequent refills. With some sensitive species, the constant moisture can lead to disease problems in damper climates when rain adds extra moisture to the garden. Usually, however, diseases are much reduced because leaves and stems are not wetted and plants are not stressed.
In his book, Fan Shengzhi describes intercropping with buried clay pots. Garlic or onions, with their small plant heads, go well with slower-growing, "spreadier" plants such as tomatoes or cilantro. Buried clay pots also make it easier to grow vegetables under trees such as eucalyptus that have aggressive and active root systems near the soil surface.
Placing buried clay pots in the garden is simple:
1. Dig a planting hole about three times as wide and two times as deep as the pot. Use a garden fork to break up soil at the bottom of the hole, and break up any clods in the soil you have removed. Mix in one-third compost or aged manure, plus amendments and fertilizers as needed. In very heavy soil, mix in some sand and organic matter; in saline or alkaline soil, add gypsum or calcium as needed.
2. Partially refill the hole with soil mix so that, when placed, the top of the buried clay pot will be about an inch above the surface of the surrounding soil. The rim on standard red clay pots makes a good soil-line marker. Then set the buried clay pot in place with the lid on.
3. Fill the space around the pot and firm it by tamping or pressing on the soil with your hands. Scoop any dirt out of the pot.
4. Fill the buried clay pot with water, add a little to the soil outside the pot, and let the soil moisten overnight. This will help you see how close to the pot the seedling or seeds should be placed. In coarse, fast-draining soils they may need to be very close to the pot. With ollas, the wider profile and narrow neck of the pot means the plants will be set further from the neck.
5. Place additional pots as needed. Pots may be placed 24 to 36 inches apart in most soils, depending on the size of the pot. Place them closer in sand and farther apart in clay-rich soil, again using the wetted area from your first pot as a guide.
6. Now you can place your seeds or plants in the wetted soil. In many soils, the seeds or plants should be placed within 1 to 3 inches of the edge of the buried clay pot. Leave a space between plants on one side of the pot to make it easier to reach the lid for refilling when the plants are fully grown.
7. Refill the buried clay pot as needed. Small pots may need to be refilled every two to five days, but larger ones only once every two to three weeks. The time will vary over the growing season. For many plants, you can let the water level drop to the bottom of the pot before refilling, but the terra cotta should remain moist.
Maintenance and Storage
Snails and slugs are easy to manage with clay pot irrigation. They tend to collect at the pot/soil seam or crawl into the pot as it dries out and can easily be removed and fed to the ducks. Fertilizer should not be included in the pot water as it may clog pores and lead to algae growth. Apply liquid fertilizer or manure tea outside the pot.
After the season is over, scrub the pots clean and stack them upside down for the winter so they do not trap water and become insect breeders. If calcium starts to build up, they can be soaked in vinegar.
Self-Filling Pot Systems
Buried clay pots are usually filled individually, but if you will be away often or don't want to bother filling them by hand, they can be connected to a reservoir or water system.
half-inch PVC pipe and fittings to connect to water line, faucet, or reservoir
half-inch pipe riser
manifold with quarter-inch connectors
quarter-inch drip tubing
flag emitters (or tubing connectors)
wire ground staples to hold tubing in place (can be made from coat hanger wire)
drill with quarter-inch ceramic bit
1. Install a ½-inch PVC pipe feed line from a manual or automatic control valve on a reservoir, pipe, or faucet to the center of the bed.
2. In the center of the bed, install a ½-inch pipe riser and a manifold with ¼-inch tubing connectors. These are commonly available at your garden or home supply stores.
Excerpted from "Gardening with Less Water"
Copyright © 2015 David A. Bainbridge.
Excerpted by permission of Storey Publishing.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.
Table of Contents
Introduction: Running Out of WaterPart 1: Super-Efficient Irrigation Systems Buried Clay Pots Porous Capsules Deep Pipes Wicks Porous Hose Buried Clay Pipe Tree SheltersPart 2: Taking It to the Next Level Water-Wise Gardening Tips Rainwater Harvesting Landscaping for Water Catchment Developing a Plan for Your Patio, Garden, Home, or Farm Our Water Future Appendix Acknowledgments Suppliers Index