How to plant successful gardens with California native plants
|By Greg Rubin|
A long-time California native landscaper explores the misconceptions and intricacies of turning a backyard into a beautiful extension of nature.
Few subjects in landscaping engender more controversy than California native plants. Most designers avoid them like a bad case of the measles. Often this is based on experience; nearly every native they’ve ever planted has died quickly, or at best lived a short, pitiful life. Drought tolerant plants that are not native to the area seem to be easier, less fussy. There may be liability issues involved as well when plants die, so it’s understandable that our own native plants take a back seat to the tried-and-true cast of characters typically seen in most drought-tolerant landscapes.
This was the state of the art that I found myself confronting in the mid-1980s. Forty to 60 percent mortality was considered normal and even acceptable. Most of the time it was blamed on the plants themselves. Everyone knows Ceanothus is short-lived, right? Okay — so then, why do they live to 100 years in the wild?
An unlikely path
I came to native landscaping from a different background than most. I was a budding aerospace engineer, still attending university but already designing native landscapes for friends and family. It was a hobby that grew into an obsession.
As an engineer, trained in logical problem solving, it didn’t make sense to me that natives were thriving on the hillside behind my house, but dying in my landscape. There was a logical disconnect there, and even while working as a successful engineer, I made it my mission to figure out why indigenous plants seemed to be such a pain to work with.
I was fortunate enough to encounter some extraordinary mentors as I began my education, chief among them the late Bert Wilson from Las Pilitas Nursery in Santa Margarita, California.
The great disconnect became quickly apparent. We in the landscape industry were attempting, often unsuccessfully, to apply traditional ornamental horticulture principles and practices to native plant landscapes. It seems that nearly everything we were taught to do with ornamental horticulture species was expressly designed to kill native plants.
700-plus native landscapes and 23 years later, we’ve found success by emulating native ecology in our installations rather than working against it. A mortality rate that once ran as high as 60 percent is now less than 10 percent. Sixty percent plant losses did not make for a viable business model, believe me. However, the emulation approach has yet to achieve universal acceptance in the landscape industry. Instead, many myths have persisted. Here are some of them.Myth #1
Drip irrigation is the best form of water delivery for all drought-tolerant plants, including natives. This is probably the one item that engenders the most controversy. Non-overhead drip irrigation, originally developed in Israel for agricultural use, might be the single greatest contributor to native plant failure. If one looks at emulating the natural ecology of native plants, clearly the only analogy to this localized hyper-saturation is marsh or streamside ecology.
Interestingly, plants that naturally occur in these conditions, such as spike rush, sedges, seep monkeyflower and others do just fine on drip. On the other hand, the more drought tolerant upland species, which form the majority of plants in low-water native landscapes, evolved over millions of years being irrigated by nature’s sprinkler — rain.
Native plants are organized into plant communities (think chaparral, coastal sage scrub, oak woodland, etc.), and are highly symbiotic within these communities. In other words, they help each other survive. Their roots are connected by mycorrhizal fungi, which, among other things, pull nutrition from inorganic soil and store water, moving these items around to where they are most needed in the community.
The fungi are adapted to receiving moisture more or less evenly over an entire area. Some of the fungi also pull nutrition from the duff layer that forms as rainwater infiltrates through this natural mulch.
Therefore, the closest way to emulate this system is with low volume, high efficiency, overhead irrigation, not with isolated zones of soil saturation that never penetrates the mulch nor washes off the leaves, which happens in nature and helps hydrate the plants.
Even grid-type drip systems don’t do this; all you do is you move from localized hyper-saturation to generalized hyper-saturation. Instead, we’ve found great success utilizing rotary nozzles such as MP rotators and similar nozzles by other manufacturers. These wash off the leaves, retard evapotranspiration, infiltrate the mulch and cover areas more or less evenly at a rate similar to a gentle rainstorm.
We use 12-inch pop-up sprinkler bodies with 30- to 40-pounds-per-square-inch pressure regulators because we need the spray to reach higher than a typical lawn sprinkler would over foliage and ground covers. We also learned not to position shrubs directly in front of the heads.
One of the limitations of rotary systems is that they’re not good at irrigating small areas and planters. We usually compensate for this by putting striptype micro sprays between any two plants in a planter. This avoids spray blockage and allows for more even watering of the containerized plants.
Micro spray heads are a great way to convert existing drip systems to overhead delivery. In the narrowest planters, we use Vortex or other multistream emitters on 6- to 12-inch stakes.
In general, watering frequency should approximate the amount of rainfall that the native plant community would naturally receive. However, in Southern California, we tend to exhibit a bias toward the high end of water tolerance to help the plants look their best. During normal winters we don’t water much, except for new plantings during the first day of a Santa Ana condition with its hot, dry winds.
In this region, we do most of our supplemental irrigation in the summer (especially in the inland areas). The amount of water deposited, normally about 0.25 to 0.5 inches, is similar to a summer thunderstorm happening about three times a month and is well within the tolerance limit of most native plant communities. Plants that evolved in the wetter, more northern areas of California may require more water.
One last note on overhead versus drip irrigation. Many exotic plants, fruit trees and vegetables do just fine on drip systems as they are not in their native environments and are immune to most of the pathogens and pests that native plants succumb to. But neither are they as potentially drought-tolerant or low maintenance as a truly native landscape is, nor do they convey a sense of regional identity or have as much value for wildlife.Myth #2
All soils must be amended, native or not.
We’ve been taught that all garden soils must be “improved” regardless of the plant species that will be deposited in it. Sandy soil? Add organic amendments. Clay soil? Add organic amendments. But if we look for natural analogs, the only type of environment that regularly experiences disturbance and high levels of organic matter is, once again, a marsh or streamside ecology. Upland, drought tolerant, mycorrhizal plant communities evolved in the absence of organic matter and fertility.
The worst thing you can do to a native plant bed is to add lots of organic matter and fertilizer to it, no matter how bad you think the soil is. One of the remarkable aspects of native plant communities is that they can tolerate a wide range of soil conditions. The key factor is drainage. With heavy clay soils, most often all you need to do is make certain that water has a path to escape so it doesn’t just sit there.
There are many exceptions to what I’ve said here, but in general, natural soils aren’t terribly restrictive, even under fill conditions, as long as the levels of toxins such as boron or salt are low. The mycorrhizal fungi, if given the right conditions to promote development, should do all the work of metabolizing the nutrients required by your native plants. Adding fertility only causes the plants to drop their fungal partners, and the soil biota convert from fungi-based to bacteria-based almost immediately.Myth #3
One need not be concerned about what plants to put together nor what mulch to use. Since native plants naturally exist in symbiotic communities, it is important to pay attention to what plants you are putting together. However, through experience, it has become apparent that the most important consideration when grouping plants is what form of mulch they prefer. Well, you have two basic choices: organic or inorganic.
Organic mulching occurs naturally when the plant communities are densely packed with evergreen, summer deciduous species and leaf litter is constantly dropping and forming a duff layer. Think chaparral, oak woodland, mixed forest or coastal sage scrub. (In fact, coastal sage scrub can take mulch or leave it; you would do just as well to put a 6- to 12- inch boulder right on top of its roots.)
Inorganic mulches consist of sand, rocks, pebbles and gravel. This predominates in plant communities that are rather open, with the plants somewhat thinly branched or in communities where the plants are small and lack substantial biomass. Desert plants would fall into the first category; coastal strand and grasslands in the second. Interestingly, you can even mix these plant communities together, as long as you give shade to coastal varieties when planting them inland or in the desert.
One type of mulch common to virtually all plant communities is rock. Nearly all native plants, regardless of the type of community they belong to, seem to love having 6- to 12-inch boulders placed right on their root balls — not in a campfire-type ring, but with just enough space for the trunks to grow. Coastal sage scrub is sort of in-between on mulch preference, but we’ve had great luck putting rocks right on its roots and then mulching between the rocks.
Rocks are a great way to keep mulch from impinging on shrub trunks and potentially rotting stems by holding moisture against them. The rocks can also provide micronutrients to the fungal grid at a very, very slow rate. In fact, mycorrhizae can secrete compounds that slow the decomposition of mulch, thus limiting the nutritional loading.
Not all organic mulches are created equal. We have found, short of grinding up chaparral, that shredded redwood bark, aka “gorilla hair,” is one of the best top dressings. Its biochemistry and slow rate of decomposition imitates the natural duff layer that forms over time, but which needs to be artificially supplied in the sort of chicken-and-egg scenario that is inevitable with new landscapes (where the plant community creates the mulch and the mulch helps determine the plant community). Gorilla hair is pricey, but well worth the investment, especially given its longevity.
The next best organic mulch is clean tree trimmings (especially if they don’t contain a lot of pepper tree). Ground oak and pine are the best in this category. The last type of mulch we would ever use is dump mulch, as it potentially contains unknown quantities of chemicals, pathogens, weed seeds and trash. Even composted, dump mulch can contain so much nitrogen from lawn clippings as to act almost like fertilizer, which is the last thing your native plants need or want. It also breaks down so quickly that it can overload plantings with nutrition.
Since the relationship between the mulch and the soil organisms is so crucial, we normally avoid using landscape fabric to control weeds. Studies have suggested that the volatile organic compounds contained in it can deter the ability of plant roots to signal mycorrhizal fungi that it’s okay to colonize them.
Regardless, the interface between the mulch and the soil substrate works better when it’s unhindered. Instead of using fabric to control the annual weeds in a new landscape, we often use pre-emergent herbicides, anticipating that additional pulling or spraying may be required for the near future. Once a native landscape achieves approximately 60 to 80 percent canopy coverage, it often develops a natural weed resistance, since the fungal ecology and lack of free nutrition often discourages weeds.Myth #4
Native gardens must look dead or dormant for half the year. The mistake most designers make is to rely solely on colorful flowering perennials and sub-shrubs. But it’s sort of “Landscaping 101” that every landscape should have a strong evergreen backbone. To avoid the dead/dormant appearance, we include about 75 percent evergreen plants of all habits and sizes with colorful leaves for texture and contrast. The other 25 percent will be color-spot perennials planted next to paths and flatwork where the color can be easily seen and maintained. Finally, we mix in perennials with different flowering periods so that something is always in bloom.
Bottom line for success
When I first started out in native landscaping, following all the usual practices — applying fertilizers, soil amendments and inappropriate mulches and installing drip irrigation — my results were as bad as everybody else’s. However, as I learned to better emulate the natural ecology, plant mortality dropped closer to 5 percent. My mantra has always been “clean, lean and mean” — clean water, lean soils and mean conditions. The result will be an easy care, truly drought tolerant, bird-and-butterfly-attracting piece of California heaven.
The author is founder and president of San Diego-based California’s Own Native Landscape Design Inc. and was recently named the 2018 Horticulturist of the Year by the San Diego Horticultural Society. He is a licensed landscape contractor who has been working with California native plants since 1985 and can be reached at email@example.com.