Native Plants and Drought Tolerance
Native plants give our landscape a sense of place and link us with the natural world. We also use them because they are known to be drought tolerant. They have adapted to thrive in California’s annual dry season, which can last six months or more.
How do we encourage drought tolerance?
Native plants are not drought proof. You cannot place any native in any situation and expect it to thrive without irrigation. For drought tolerant landscaping, you need the right plant in the right place, with the correct initial care. With good selection and placement, along with an appropriate establishment period, natives can grow in your landscape with little or no irrigation.
Choose a palette of plants that should grow at your site with little or no irrigation
The first option is to evaluate your landscape conditions and see what is growing in your area. Choose a native plant community that you think would grow in this situation. By trying to recreate a natural plant community, your are matching the plants to the site. This is the system we use in designing restoration projects, and is a great way to reduce the need for long term maintenance and irrigation. If you get it right, the plants, once established, will grow and perform as they would in a natural setting. However, even with knowledge, experience and good observational skills, you may or may not be correct in your plant choices. Be ready to adjust your plant palette according to what works or fails. We are constantly surprised when a plant species will not grow where it should, and also when a plant grows beautifully where it shouldn’t. The site determines what works, and you need to work with it.
The second option is to develop a native plant community that is different from what previously existed on your site. This can still be a ecologically valid choice, because there are usually at least two distinct plant communities that can grow on any given site. They can represent various stages in succession, or they can be different climax communities. As a general rule, it is easier to grow shrubs, grasses and perennials in a opened woodland site than it is to grow a woodland in a former shrub or grassland site. Changing the plant community can work beautifully, however, once you depart from the predominant community in the area, your level of risk may increase, along with your need for outside inputs (eg - water, soil amendments, fertilizer).
Train the roots for drought tolerance
There are two important rules to foster drought tolerance. The first rule is to irrigate deeply, so that the water penetrates down through the root system, and hopefully meets with the stable moisture supply below. The second rule is to irrigate as infrequently as possible.
The best way to water is with a drip irrigation system, which allows you to bring water to the root system of each individual plant. For most purposes, we use 1/2 gal per hr or 1 gal per hr emitters. If the root system is relatively narrow, one emitter is good enough. If the root system is wide, as for 5 and 15 gallon stock, you may need to space two or more emitters across the root ball. If you don’t want to install a drip system, you can use a garden hose, and make it run as slowly as possible. It’s more labor intensive, because you need to keep moving the hose, but it works great. Leave the system on long enough that the water penetrates at least two feet into the ground. This can take two to three hours.
By contrast, overhead sprinklers. use a great deal of water, but only irrigate at the surface. The only time to use overhead sprinklers is for patches of small plants, in which case, you use low volume, small sprinklers.
You will be tempted to water two or three times per week, especially during the summer. You will also be tempted to use an automatic timer. Regular, frequent irrigation is great for conventional landscaping but not for drought tolerant landscaping. If you water often, the plants will appear very healthy and vigorous, but they will be totally dependent on continued irrigation. They will decline as soon as you stop watering.
To encourage drought tolerance, the plants must be forced to grow deep roots, so they will find a stable water source. This means watering as infrequently as possible. Depending on the plant, the location, the soil, etc., the interval can be anywhere from two weeks to three months. Carefully monitor the plants for stress, such as wilted leaves, poor color, etc.
Some plants will perform beautifully. Others will die, or continually appear on the edge of failure. Rather that trying to nurse them for too long, consider replacing them with something else that might work better.