Irrigation secrets of the ancients

Don’t hestitate, irrigate

The newest techniques for conserving water in the garden are actually more than a thousand years old.

American Indians survived for centuries in the desert by harvesting rainwater to grow crops. And while today’s water supply may not be as scarce, gardeners still can tap into ancient water-saving strategies to make the most of every drop.

“Trends in water conservation are becoming more accepted because people are realizing water resources are limited,” says Joel Glanzberg, a designer with an environmental planning firm in Santa Fe. Glanzberg, who has written about water-harvesting traditions in the Southwest, says these systems can offer today’s gardeners lessons in conservation.

Dryland farmers, for instance, needed to collect moisture and hold on to it for as long as possible. The two main techniques used were to sink the planting areas and to mulch with rock.

The Zuni in New Mexico used sunken beds called waffle gardens for growing high-value crops like tobacco and chiles. Modern kitchen gardens can benefit from this prehistoric technology.

“Waffle gardens work just like a waffle, with the plants placed where the syrup would go,”

Glanzberg says. Ground-level berms surround each 2-foot-square planting area. The berms are several inches high and built with unamended soil. The depressions catch and hold water close to the plant’s roots.

Grid gardens are similar, with 10-foot-square grids bordered with rocks. Larger versions of grid gardens have been used in the Southwest and also for dryland farming throughout the world.

Both waffle and grid gardens are mulched with gravel, sand, or rock. Rock mulch conserves water by shading the soil and slowing evaporation. Gravel-sized mulch is most effective during a hard rain because it allows water to be pulled down into the soil and reduces runoff.

“Unlike organic mulching materials that absorb a lot of rain water, gravel mulch lets all the water flow through to the soil below,” says David Salman, president of Santa Fe Greenhouses.

To be effective, he says, gravel must be 2-3 inches deep.

“Contrary to what is commonly believed, gravel mulch is highly beneficial to plants and the reflected heat is not a problem, particularly when planting in the fall and spring,” Salman says.

Glanzberg estimates gardeners could save half of their garden water with these techniques.

“There was a study done at one Pueblo where two beds of corn were planted adjacent to one another. One bed wasn’t mulched, and it was watered once a week. The other bed was covered with rock mulch and received no irrigation. There was no discernible difference in the two crops at the end of the growing season.”

The gravel mulch acts as a dew trap to capture condensation. Gardeners can see this firsthand, he says. “Just pick up any rock in your yard. It’s likely to be wet underneath.”

Dark gravel mulch functions like Wall-o’-Water plant protectors by absorbing heat from the sun to keep plants warm at night and extending the growing season for tomatoes and eggplant. It also allowed cotton to be grown in the southwest, where it was normally too cold to grow, Glanzberg says.

Glanzberg also recommends another way to conserve water: Follow nature’s lead by using cluster plantings. When plants with similar needs are placed together, a microclimate is created and less water is used.

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“Plant form is important here, so crops like cabbage and carrots have different structures of roots and leaf growth that complement one another. Fruit trees with berry bushes below and a ground cover of strawberries and flowers is another example.

In nature we can see the pinon growing in clumps with juniper, shrubs such as currants grow beneath with cacti, desert four-o’clocks, and grasses. This is what we are copying.”
A variation on cluster plantings is companion planting. American Indians understood the benefit of planting corn, beans and squash together. These vegetables are called “three sisters” because they complement each other in the garden. Corn provides tall stalks for the beans to climb. Beans help replenish the soil with nutrients. Squash leaves act as living mulch.

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The three sisters can be planted in a waffle garden with corn in the middle of the planting hole, beans surrounding the corn, and squash planted in one or two corners.

Buried clay pot irrigation is another ancient water-saving method used in places of perennial drought like Mexico, Central America, Asia and Africa. It’s estimated to be two times as effective as drip irrigation and 10 times more efficient than conventional surface irrigation. While large earthen jars were used 2,000 years ago, today, red, unglazed clay pots work as well.

Cover the hole at the bottom of the pot with masking tape and seal it with silicon caulk. When dry, bury the pot to its lip in the garden. Place plants or seeds close to the pot. Fill the pot with water and cover with a simple lid, such as an aluminum pie tin. Fill the pot as needed. The water will seep through the pores of the pot, keeping the soil moist.

Delivering water directly to the roots has two advantages: plants receive a constant supply during the growing season and weeds are kept to a minimum. Buried clay-pot irrigation can be used to grow annuals, perennials and container gardens.

The Anasazi at Mesa Verde also were skilled at wringing water from dry lands. Kenneth Wright, a consulting engineer with Wright Water Engineers, studied the prehistoric public works structures at Mesa Verde since 1995, working to discover how ancestral Puebloans created a water supply on a riverless mesa.

“The early people of Mesa Verde were good engineers,” he says. “They knew how to harvest water where modern engineers would judge there to be no water.”

Wright is a paleohydrologist – one who studies the ancient use and handling of water.

In his book, “Water for the Anasazi: How the Ancients of Mesa Verde Engineered Public Works,” Wright details how inhabitants created a water system that sustained the population. Small dams and diversions collected rain and reservoirs stored the water.

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“They knew how to harvest water, store water and pass that knowledge on.”

That knowledge was essential during long periods of drought, one lasting more than 50 years. Wright suggests that Coloradans look at drought historically and prepare for it.

“One thing we can learn from these ancient people is that you can make do with little. We should be willing to pay more for our water and do with less.”