Carolyn Singer: Water-efficient & drought-tolerant: Plants adapted to foothill climate conditions
With no summer fog rolling over the gentle slopes of the Sierra foothills, “full sun” plants are brutally exposed to summer heat and low humidity. Nursery labels advising full sun seldom reflect this critical information.
A plant growing in full sun near the California coast may thrive, while the same plant growing inland in the valley or foothills may suffer in summer heat.
In visits to the Fort Bragg Botanical Garden and the Center for Urban Horticulture in Seattle, I have marveled at the form, beauty, and lengthened bloom cycle of several landscape plants growing in cooler summer climates with higher humidity.
If the plant in question growing near the Pacific Ocean has not been irrigated during typical summer dry periods, it may be heralded as “drought-tolerant” in the truest sense of the label.
No irrigation other than natural rainfall, even during drought years. Or at least in the coastal climates. However, planted in your Sierra foothill garden, the same plant may require frequent irrigation or some afternoon shade, or both.
“Water-efficient” is an evaluation now being used in the landscape industry. With the passage in California of the Municipal Water Efficiency Landscape Ordinance, cities and homeowners within those city limits are required to select plants that meet the criteria for water usage.
While the provisions of the ordinance apply to new landscapes and larger renovations, all homeowners should be considering responsible choices.
Not only do plants need to be introduced into the landscape based on their defined water-efficiency, they must also be zoned. Plants with similar requirements should be grouped together.
Keeping plant groups together
In my rock garden, I test three parameters. Will the plant take full sun all day? Will the deer leave it alone? And, most importantly, will the summer irrigation schedule of a deep watering once every three weeks be adequate?
Newly planted rock garden perennials receive water once a week for the first two years, until they are considered established.
It is significant to note that a perennial described as drought-tolerant or water-efficient may become a pest if it is over-watered.
An example is the dwarf form of germander (Teucrium x lucidrys “Compacta”), an excellent evergreen pollinator groundcover in sun to part shade, with deep watering every two to three weeks. To deliver more irrigation will result in rampant spread.
The same may be said for sweet woodruff (Galium odoratum), a very desirable perennial for dry shade.
Given too much water in summer when it is growing actively, and it will soon march on your other shade plants. This is not a problem if they are shrubs, but smaller desirable perennials may be overwhelmed.
In some garden areas, I have non-native trees, ornamental shrubs, perennials, and bulbs that receive no irrigation in the dry summer months. I’m sure they welcome that first fall rain as much as I do. A big sigh of relief.
One of my favorite non-native trees for maximum water efficiency is the hawthorn (Crataegus), often called May tree, as it is in bloom just in time to provide sprays of flowers for May Day celebrations and arrangements.
I have never given it summer water, and during the most recent drought years it was a survivor with no supplemental water. Definitely “drought-tolerant.”
May tree thrives in full sun or part shade, doing quite well in the rocky clay typical of the Sierra foothills. To minimize maintenance (there is none) I have allowed my white hawthorn to grow as a multi-stemmed small tree. My mature specimen is now thirty feet in height.
Hawthorn is also valued by naturalists for its medicinal properties.
It is important to remember that not all natives are either water-efficient or drought-tolerant. Some thrive in moister canyons.
Learn about cultural requirements and decide whether a native is appropriate for your garden before you purchase the plant.
Excellent references to guide you include two books compiled by our local Redbud chapter of the California Native Plant Society: “Trees and Shrubs” and “Wildflowers.”
Carolyn Singer has gardened organically in Nevada County since 1977. She is the author of the award-winning “The Seasoned Gardener, 5 decades of sustainable and practical garden wisdom”, and two volumes of “Deer in My Garden” (deer-resistant plants), available locally. Send your gardening questions and comments to firstname.lastname@example.org. Check out her website at carolynsingergardens.com.
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