This low-tech irrigation system you can make yourself lets plants draw only the water they need. That means less wasted water (and time) and better gardening results.
Porous capsule irrigation is a modern adaptation of buried clay pot irrigation. Water is distributed automatically and continuously by gravity in direct proportion to water use by the plant, leading to very high efficiency. Typically set up to run off a storage tank, bucket, bottle, or pressurized water line, porous capsules can be networked more easily than pots and completely buried. Though you cannot see the water level inside the capsules, burying them reduces the risk of damage, helps keep dirt and bugs out, and minimizes evaporation. Porous capsules can improve soil and allow for agricultural development in areas where climate and soil quality have prevented the use of conventional irrigation methods.
Most porous capsules have a volume between a quart and a gallon, and they can come in many shapes and forms: pots, ollas, pipelike sections, vertical cylinders, bottles, and flasks. Each porous capsule may have one to four connectors. The pipes and connectors tend to be relatively large in diameter so that they require little or no filtration. If capsules are used in a series, the water readily moves down the line as water is introduced.
Not only are porous capsules useful in greenhouses or in the field, they can be excellent for plantscaping interiors as well. A large reservoir can offer a very long refill interval for a plant. A wide range of capsule systems for small plants have been developed and sold over the years, manufactured in China, Vietnam, Thailand, and the United States. These are often called plant sitters, plant tenders, water spikes, or ceramic waterers. Some attach to a wine or water bottle and some use a glass sphere as a reservoir, making it easy to monitor water use. Others include tubing that connects to an exterior tank. You can ask for these at local garden shops or find them online. Even Chia Pets, in their many varieties, are a form of porous capsule or clay pot irrigation.
Porous capsules are more costly to make and install than buried clay pots or deep pipes, but in arid environments they will pay for themselves in yield increases, water savings, and reduced weeding time.
Garden with Porous Capsules
Porous capsules work very well in the garden. Dig a hole for each capsule much like for a buried clay pot. The top of a capsule may be buried 2-4 inches, but with a taller capsule made of two pots, I may leave the top near the surface.
The capsules can be attached to bottles or outfitted with refill funnels. However, creating a network of capsules will reduce management time for rows of plants. To do this, simply attach a T-fitting to each pot so that it can be connected by tubing to other capsules in a continuous line. The crop will determine spacing, perhaps 2 feet with non-spreading plants and up to 6 feet for melons and squash. If you place the capsules on a slope, water delivery will be greater at the low end, so set them along the contour line to keep them as level as possible.
With another barbed plastic fitting, connect the capsules to a reservoir (such as a 5-gallon bucket) with, perhaps, zero head at the start of the season. The reservoir can then be lifted up to about 18 inches during the maximum growth period to increase water flow. The reservoir can be refilled using a hose or set up with a float valve or timer valve to fill automatically. At the end of the line of pots, an open vent should be made with tubing or hose. This should extend above the soil to the height of the reservoir to vent air from the system.
Although porous capsules are not as sensitive to clogging as drip emitters, they may eventually clog from sediment or bacterial, fungal, or algal growth. If possible, use a simple 500-mesh filter on the reservoir line or water line to prevent debris from getting into the capsules.
Low Pressure or No Pressure?
Rainwater from a roof catchment system is ideal for use with porous capsules, because capsules work well at low pressure and the rainwater is salt free. A nice gravity-fed system can be created by connecting a line of porous capsules to a rain barrel.
Capsules used on greenhouse benches or in raised beds can be run at negative pressure, with the reservoir sitting below the capsule. These systems have to be sealed, and the pots are filled the first time by lifting the reservoir (such as a five-gallon bucket) above the capsules until they are filled.
Making Porous Capsules
Standard red clay garden terra-cotta pots and pot bases make good porous capsules when glued together. Test the porosity and durability of pots and pot bases before ordering or making a large number of capsules.
- Terra-cotta pot and base
- ½-inch threaded-to-barbed plastic fitting
- Polyurethane glue or epoxy
- Lightly sand the rim of the pot and pot base on a full sheet of sandpaper (100 to 200 grit) to create a flat surface that will make a watertight joint.
- Glue the plastic fitting into the hole in the pot (follow directions and precautions on glue label). The threads should fit the hole. If the hole in the pot needs to be increased, you can enlarge it with a masonry bit or sandpaper wrapped around a dowel. If the hole is too large, use glue to fill small gaps, or use the rubber stopped method described in Alternative Methods.
- Spread a layer of glue on the rum of the pot and glue the pot and pot base together.
Alternative Methods: You can also use two pots of the same size, glued together, with rubber stoppers to seal the holes. A drip-tubing connector will fit snuggly into a 3/16-inch hole drilled through a rubber stopper.
Text excerpted from Gardening with Less Water © 2015 by David A. Bainbridge. All rights reserved.