The nifty water delivery system of an olla was introduced in last week’s Gardening for You column (July 19). An olla (OY-yah) is a porous clay pot that supplies water directly to a plant’s root zone. Water molecules pass through the pores of the clay into the surrounding soil; it is passive movement, not requiring an external energy input.
Water moves from a higher concentration in the pot to a lower concentration in the soil, seeping slowly into the soil until the water concentration in the pot is the same as in the soil. Water movement ceases when this equilibrium is reached. As surrounding soil dries, water movement from the pot resumes.
Shape and size.
The classic olla shape is ovate: think egg-shaped with a chimney funnel on the top that becomes the neck. Tapered necks reduce ground surface evaporation; ollas with larger necks are still effective but may need more frequent refilling.
Small ollas are used for container-grown plants; larger ollas that deliver larger quantities are used in raised beds and in-the-ground gardens. Small ollas that hold a quart of water are about 5 inches in diameter and 7 inches in length; an olla of this size delivers water 18 inches to 2 feet in diameter. Larger ollas that hold up larger quantities deliver water up to a 3-foot radius.
Placement.
Ollas discharge water in a circular radius. Dig a hole large enough to submerge the olla keeping the neck exposed. Tightly pack soil around the pot to ensure there are no air holes as water moves by passive capillary action soil particle to particle. Since the pattern of the water as it moves into the surrounding soil is spherical, overlap ollas in raised beds 2 to 3 feet apart and large ollas for in-the-ground gardens 3 to 4 feet apart.
Best crops.
Crops with fibrous root systems benefit the most when irrigated with ollas: melons, peppers, squash, tomatoes and spring greens. Plant lettuces and other salad greens to encircle the olla to make the most use of the moisture as it seeps into the soil. Crops with taproots like carrots and beets are difficult to irrigate with ollas. Space plants in the appropriate radii from the olla.
Sources.
Local sources are difficult to find. Mary Lee’s Gardens on 82nd Street has carried them but is sold out for the season. Several online sources: Dripping Spring Ollas, The Olla Company, Epic Gardening, Territorial Seed.
DIY.
Choose unglazed terra cotta pots that hold the quantity of water needed for its use. Deep pots work better than shallow, wide pots. Small pots for smaller areas, large pots for larger areas. Two pots can be stacked to provide deeper moisture. Fill drainage holes with non-porous material like Gorilla glue or corks set in with caulking. Bury the pot within a foot of where plants will be grown, keeping the neck above the soil surface. Cover with a terra cotta saucer.
This makes for a good summer project!
Ellen Peffley taught horticulture at the college level for 28 years, 25 of those at Texas Tech, during which time she developed two onion varieties. She is now the sole proprietor of From the Garden, a market garden farmette. You can email her at [email protected]
This article originally appeared on Lubbock Avalanche-Journal: Gardening for You: DIY ollas