A Guide to Watering California Native Plants
By Josh Williams
Understanding how to water California native plants is one of the most important and least understood aspects of creating a healthy and flourishing native garden. We get asked about irrigation nearly every day: Do I water my natives once a week for their entire lifetime, or, since they’re drought tolerant, should I leave them alone as soon as they get in the ground? Hopefully, this guide will help answer some of your questions.
Adaptation to California’s climates
Much of traditional Western Gardening traces its roots to Northern and Central Europe, where plants received ample summer rain. Throughout our horticultural history, we’ve been trained to desire a lush and verdant landscape with species that require regular irrigation. These old habits can be difficult to break.
Most of California’s native plant species are adapted to a Mediterranean climate, where winters are cool and moist, but summers are warm and dry. When we keep our natives too hydrated in the summer, the combination of warmth and excessive moisture can cause microbes in the roots and stems to flourish, inhibiting the uptake of water. What is essentially happening is your plants are not absorbing enough moisture, which is why a drought stressed plant can look similar to one that is overwatered. In winter, when the weather is cooler and species are accustomed to receiving regular rain, this problem is much less likely to arise. This is why it is important to water established plants on cooler days in the summer, either in the evening or the early morning.
Cool and moist = happy!
Warm and wet = dead!
Of course, there are exceptions. Plants that grow along streams or along our coastline are adapted to having regular access to moisture and will require that in your garden.
It’s helpful to know where your plants came from so you can replicate those conditions in your own garden, while possibly adding a little extra water for aesthetics and fire safety.
Timing: Water Determines When to Plant
The golden time to plant is fall, when the days are shorter and cooler, and there is a greater chance of rain. Winter is still excellent, though in colder weather, plants may be slower to establish. Spring is good for somewhat cold sensitive species and those which need a little babying at first, such as sages (Salvia spp.) and California fuchsia (Epilobium spp.). While summer is the least suitable time to plant, it can be done, especially with smaller perennials, if a close eye is kept on the irrigation.
Autumn and Winter Planting
When planting during the rainy season, minimal irrigation is usually required. However, during dry spells you will probably need to do some watering. Most of our native plants have adapted to moist winters. This is the time of year they expect to receive a good dousing. Even established plants like oaks can benefit from deep watering during winter droughts, since they’ve evolved to get that winter rain. Mimic a wet winter!
Warm/Dry-season planting
Regular water is needed at first when planting during our long summers. Plants will need irrigation until the winter rains begin. Water on cooler days, early in the morning, or in the evening. Pay close attention to the soil around the root ball and make sure it doesn’t get too dry.
How to Water When Planting
When installing a new plant, make sure to water it well in the container before transplanting. It’s also advisable to fill the planting hole with water and let it drain completely before placing your plant in the hole. Once you have planted your specimen, water it thoroughly to settle it in.
Sculpting a circular berm around your new plant creates a reservoir to hold water in place and allows for easier and more thorough watering. This is particularly important when your plant is new and needs attentive hand watering. Fill the basin at least two times to ensure the water absorbs deeply into the ground.
A layer of mulch around your plants helps to keep the soil cool and moist. Gravel mulch works particularly well for species native to dry, rocky soils, and allows for the application of wildflower seeds. It’s also a firesafe option. A wood chip mulch helps to keep weeds down, but should be kept at least 6 inches away from the base of woody plants to prevent rot.
Establishing New Plants
Newly installed plants will require more irrigation than established ones since their roots have yet to expand into the surrounding soil. You will need to begin by watering them very frequently. Hand watering is the best way to irrigate new plants. For the first couple of weeks, try the finger test: stick your finger into the soil around the root ball up to your first knuckle. If it’s dry, water!
As time progresses, the new plants will need less and less water. There is not a “one size fits all” formula for establishing newly installed gardens, but here are some general guidelines:
When first planting, you will need to water as often as every day during warm weather.
Over time, deeper soaks will be required to reach the new roots as they grow downwards and horizontally, but you won’t have to water as frequently.
For many drought tolerant perennials, you might start by watering every other day and after two weeks decrease to once every 3 or 4 days.
A month after planting, you might only be watering once every 7 to 10 days. For example, if you are installing in spring, your new plants might only need once a-month irrigation by the end of summer.
Drought tolerant shrubs take longer to establish and may not be fully drought tolerant for up to 3 years. After the first year, once a-month irrigation will probably be required during the dry season.
When you are watering your plants, make sure to water for a longer duration. This allows the water to sink deep into the ground where it will reach the plants lowest roots and help to make the plant more drought tolerant. In a way, it helps pull the roots deeper into the soil so they can reach water when the surface soil is dry. Not only will this make plants more drought tolerant over time, but with deeper and less frequent soaks, the surface roots will remain drier and less prone to disease.
Long Term Irrigation: Water Needs for Established Plants
Irrigation needs for your plant depend on various conditions such as sun exposure, soil composition, and location (distance from the coast). Because of this, you may see multiple water requirements listed on our signs for a given plant due to these different factors. Even though we list multiple watering categories, that doesn’t necessarily mean they will all be tolerated in your locality or garden.
For example: If you live in a hot interior location with fast draining soil and full sun, most plants you choose will require more moisture. If you reside in a cooler more coastal area with heavy soil and a little shade, less irrigation will be needed.
Here is how we categorize our water requirements at the nursery. Keep in mind, this refers to established plants. Most plants take one to three years to become established.
Regular: This plant requires water every 3-7 days
Moderate: This plant requires water every 7-14 days
Occasional: This plant requires water every 2-4 weeks
Infrequent: This plant requires water every 4-6 weeks
Dry: This plant survives on rainfall once established, except during periods of prolonged winter drought
Irrigation Systems and Techniques:
Many gardeners choose to use automated irrigation systems instead of hand watering, especially for larger areas. These have the advantages of being thorough and regularly scheduled, but one still needs to periodically check to make sure they are functioning and to see if the plants are getting the irrigation they need. Moveable sprinklers can be a happy a medium, allowing one to keep a close eye on what is being watered, but still irrigating a larger area in one fell swoop.
Microspray: These systems are made up of a series of overlapping emitters on stakes which produce a fine spray over the planting area. Many native plant enthusiasts prefer microspray for its even coverage and rain-like qualities that are especially good for spreading plants. However, drip emitters are better at conserving water and will be beneficial to certain temperamental plants that dislike getting their leaves wet.
Since water is spread out over a broad area with microspray, you will need to make the watering duration longer than it would be for drip irrigation. Durations of at least 45 minutes will be needed for new plants, while established plants will need at least an hour. Emitters can clog and need to be checked regularly.
Drip Emitter Systems: This system utilizes button-like sprinklers which slowly release water from a network of spaghetti poly tubing. Since drip emitters are very localized and focused on a particular spot, less time will be needed for irrigation. New plants should be watered for at least 30 minutes while more established plants should need about 45 minutes.
Some landscapers prefer to use inline drip emitters which are embedded into larger tubing and laid out in a matrix through the garden. While it does irrigate the ground more evenly, it uses a lot of plastic and is harder to unclog. For large specimens such as shrubs and trees, several emitters will be needed, running for about an hour so the water can reach all the way down to the lowest roots.
When first installing drip, make sure to place the emitters on top of the root ball. After a year or so, you will need to move them away from the trunk to reach the spreading roots and add more emitters. As with microspray, emitters do get clogged easily and should be checked regularly.
MP Rotators:
This very low maintenance system is set up like traditional lawn sprinklers, with underground pvc pipes supplying a matrix of pop-up sprinkler heads. Unlike typical lawn sprinklers, the heads produce a high arching, low volume flow with larger droplets to reduce water loss to the air. The low pressure requirements mean quite a few heads can be installed on one line, allowing for coverage of large areas and use on properties with weaker water flow. Run times typically should be for about 2 hours. While installation does take some work, the system is surprisingly trouble-free once it’s up and running. Generally only suitable for somewhat larger gardens since the sprinklers have a spray radius ranging from 8.5’ to 30’.
Moveable Overhead Sprinklers:
Good old Rainbird sprinklers on tripods and the classic “Pound of Rain” are very serviceable and affordable ways of making your life a little easier in the garden. They are simple to move and provide a nice, rain-like dousing. Depending on the style and the placement, they should generally be left on for 1 – 3 hours. Consider adding a timer to your hose bib so you don’t have to remember when to turn them off.
Hand Watering:
When you really want to keep a close eye on your plants or you’ve just gotten them into the ground, nothing beats just doing it by hand. Just remember it can take quite a while to water thoroughly enough to soak all the way down to the lowest roots. For established shrubs or trees, consider placing a hose at their base and turning it on at a trickle. Leave it there for an hour or so for good saturation.
Sonoma County sources for irrigation supplies:
Harmony Farm Supply in Sebastopol: Excellent for home gardeners.
Wyatt Irrigation Supply in Santa Rosa: Good for large installations.
A note about dry gardens: Health and Fire Safety
A truly dry garden which doesn’t receive any supplemental summer irrigation can work very well for some people, but can have some drawbacks. A once a month soak on a cool morning can help to keep plants looking a little healthier and more verdant, especially during drought years and hot summers. Infrequent irrigation can also aid with fire safety, helping plants to retain a little extra moisture and make them a little more fire resistant. Most natives, even those from naturally dry areas, appreciate a little water in the dry season.
