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Irrigation in Restoration Projects

The irrigation schedule is determined primarily by the landscape type (conventional landscape vs restoration). The schedule is further modified by the types of plants used (perennials, woody plants or grasses and sedges) and the site conditions (cool and foggy along the coast, warm and dry inland, etc.).

"Restoration" means that you are trying to recreate or restart a fully natural plant community. This implies that irrigation will eventually be ended. The plants should eventually live by natural moisture alone.

Local Soil and Hydrologic Conditions
One of the best lessons I ever received was from Rod Arkley, a professor in a soils class. He told us "If you want to know about the quality of a soil, look how tall the weeds grow." You can, and should get soils tests, but the best indicators of soil quality are the plant species that grow there and their vigor.

Before designing a plant community or irrigation system, you should start to learn the local soil and hydrologic conditions, in order to understand where certain plants or groups of plants can thrive. Restoration planners try to do this as they prepare restoration plans, but this is often impossible to do in a short period of time. We find that it takes us a year or more before we begin to understand the intricacies of a given site. We need to see it perform during all four seasons of the year. Restoration plans are performed with the best of intentions, but with limited on site experience. As a result, restoration plans get some things right and others wrong. Don't be too fixed on the restoration plan. It is a starting point. Be ready to change and adapt to the actual conditions and plant responses.

Root Training and Depth of Watering
If you water multiple times per week, you maintain moisture near the surface. This encourages feeder roots near the surface, which is great as long as the plant remains irrigated. Such a plant, however, becomes totally dependent upon irrigation, because it will not have enough deep roots, where the moisture level is stable late into the summer. These plants will show moisture stress if irrigation is interrupted.

When irrigating a restoration project, it is better to water infrequently but deeply. This will encourage deep rooting, as the plants' roots will seek a stable water supply. The more infrequent the better. Many people water every week or two, but you will find that you can wait one or two months between waterings. When you do water, make sure you encourage the water to go deep into the soil rather than spread at the surface. This is accomplished with a drip system or an open hose that applies water at a slow rate (1/2 - 1 gal per hour), but is left on for a number of hours. Overhead irrigation by sprinklers will not work for this purpose.

Acceptable Level of Mortality
If you water infrequently, many plants will perform poorly or die. You will be tempted to increase the level of irrigation or to amend the soil. This works great for landscapes, but is ultimately self defeating in a restoration. If the plant is performing poorly with limited irrigation, it is likely to perform poorly in the future, when you eventually cut off the irrigation. Adjust your plantling layout, rather than the amount of irrigation.

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