How to have a Native Plant Garden
Part 2: Site and Soil
Article and photos by Peyton Ellas
In December I wrote about the first step in planning your native plant garden. Since successful gardens are always changing, planning never really ends, but this dedicated time when you first begin, and again periodically, can really help budget time and material resources. Even if you have an established garden, it's good to periodically revisit the idea of the garden and determine if everything is still working or if changes need to be made.
Concha Ceanothus and Lilac Verbena (Verbena lilacina de la Mina) both love the sandy loam and summer shade from a Western Sycamore (Platanus racemosa) in this Central California garden that used to be an orange grove.
An often overlooked step in the planning process is “site analysis.” Explore your yard with a shovel and notepad or mobile device in hand, to determine what kind of soil you have, how the water flows and drains, how many hours of sunlight different areas receive. Note north-facing and south-facing areas, flow and characteristics of wind, and views that need to be blocked or featured.
How are the existing plants doing? If you know the names, what species are growing well in different areas, and what species are struggling? We can learn a lot from what plants already do well both in our yards and in our neighbors', even if the plants are not native or Mediterranean-climate species. For this exercise, weeds count as plants too! If you have a field of weeds, take photos or note which ones are growing well and learn what conditions they favor.
Quail bush (Atriplex lentiformis ssp. breweri) is more often a large shrub, but can be kept small by consistent pruning, and it is an excellent "soil healer," tolerating a range of conditons.
I often hear from people who believe their soil is “terrible,” but the only truly terrible soil is sterile, filled with pathogens or an over-abundance of salt or boron. And even for these, there are some plants that will grow, and soil can be improved or healed. True clay soil is rare; adobe, even more so. Most soils are fine for a wide range of native plants. “Terrible” soils often turn out often to be sandy or granite-loams, found in vast stretches of California and terrific for a large variety of native plants that care more about good-draining soil than nitrogen. When I hear that someone lives near a water-way and has “terrible” soil with “a lot of rocks,” I know they will likely have success with plants that are tricky to grow elsewhere, among them some of the most beautiful and interesting of our native species.
“Clay” soil is often “loamy-clay,” the type of soil found in large stretches of California's agricultural areas and in the alluvial valleys. In rural areas, orange and olive trees are often planted in these soils. Planting native plants on old orange groves is a challenge when there are residual minerals in the soil left over from farming, but these soils in general have a moderate-draining capacity and are fine for a wide range of native plants from all over the State. Soils in which walnut trees are planted are often sandy-loams or lighter degrees of clay-loam or sometimes loamy-sand, and these are among the best soils for native plants. Again, residue from over-fertilization or lack of the necessary micro-organisms in the soil due to years of mono-cropping and pesticide use are sometimes the greatest challenges to establishing a native plant garden. Not the soil itself. In these cases, planting soil-restorative species like quail bush (Atriplex lentiformis ssp. breweri) and some of the woody sages can be enormously helpful in the first five years of a new garden. Many cities are built over alluvial loam and loamy-clay. Soils in urban areas are generally the best loams, although fill soil is often brought in for subdivisions, and so you may have a three or more foot-deep layer of a “foreign” soil covering the native soil beneath. Sometimes your research means finding out about both the top fill layer and the original layers beneath it.
To test soil drainage, dig a hole about 1 foot deep. Fill with water and allow it to drain completely. Immediately refill the hole and measure the depth of the water with a ruler. After 15 minutes, measure the drop in water in inches, and multiply by 4 to calculate how much water drains in an hour.
Less than 1 inch per hour is poor drainage, and plants that don't tolerate poor drainage will suffer. This includes most of the species that originate in chaparral or sage scrub wild communities. Look for indicators such as “tolerates clay” on plant descriptions to know which plants will work in poor-draining soils.
One to six inches of drainage per hour is well-draining. Soils that drain faster than six inches per hour are fast-draining.
This is a generalization of course, which is why I suggest you do your own analysis to discover what are the characteristics of your particular garden site. All of this may take some hours of effort. But as gardeners, we probably are more interested in learning about our soils than the average, and then you can be an expert for your neighbors once they start asking about those beautiful, thriving native plants in your yard.
Peyton Ellas is a landscape designer specializing in California native plant-based gardens in California's southern Central Valley. She can be reached through her website: QuercusLandscapeDesign.com.