Drought-Tolerant Dwarf Conifers
Most of us have long recognized the wisdom (although we often stubbornly refuse to heed it) of “right plant, right place.” Gardening success comes most easily when we choose plants that are suitable for the climate and setting. For Sonoma County, that means selecting plants that can withstand our Mediterranean climate and frequent droughts.
Conifer lovers are fortunate, because compared to many other kinds of plants, evergreen conifers, in general, are well prepared to deal with adverse conditions. For gardeners concerned about fire safety, planting dwarf forms makes the most sense.
The first place to look, when seeking conifers that will do well in our gardens, is in our California native plant population where there are over 50 native conifers, about half of which have many garden-appropriate cultivars. Some of the darlings of conifer collectors are among native genera: Pinus contorta ‘Chief Joseph’ and ‘Taylor’s Sunburst’ and Picea engelmannii, ‘Bush’s Lace’ and ‘Blue Harbor’. These cannot be classified, however, as fully low-water conifers.
When seeking natives, focus on those that can handle the specific extreme to which you will be subjecting them. Cupressus macrocarpa (Monterey cypress), for example, withstands low rainfall, poor soils and Pacific gales, so is an appropriate California native conifer for low-water situations. The garden cultivars are lovely, particularly ‘Coneybearii Aurea’ and ‘Greenstead Magnificent’.
Going native sounds good, but doesn’t always produce the best choices. Even better than many natives, the conifers that truly seem to deal with the dry summers and extended periods between waterings are those that are native to regions with extreme conditions. The Mediterranean conifers, for example, are naturally equipped to handle less-frequent waterings. Abies pinsapo, or Spanish fir, (with some great cultivars such as ‘Horstmann’, ‘Glauca’ and ‘Aurea’) and dwarf cultivars of some of the cedars, such as Cedrus libani and Cedrus atlantica, are standout performers. Once established, they can handle much less-frequent waterings than Sequoia sempervirens cultivars, for example. There is a wide range of size, color and form amongst the cedar cultivars, so you can have a lot of variety within this one genus.
Conifers from other regions, such as those with mountainous terrain with irregular rainfall, appear to be able to soldier through less-than ideal conditions and still look attractive. Colorado blue spruce (Picea pungens) is prized for its intense blue color that results from wax on the needles believed to reduce their temperature, as well as transpiration and light absorption. That protective wax helps retain moisture and deal with low-water conditions. Numerous low-growing, dwarf spruces are well suited to our Mediterranean climate.
Pinus mugo hails from mountainous regions of Europe and Asia, many of which suffer severe, desiccating winds. Consequently, mugos have developed tough needles to retard water loss, enabling them to handle our dry summers. They have an exceptionally large native range, which yields the longest list of synonyms of any pine and a dizzying array of variation among the cultivars. Some, such as ‘Mops’, ‘Sherwood Compact’, ‘Slowmound’ and ‘White Bud’ are reliably slow growing, so if you select one of these, you will avoid the dreaded guessing game of wondering how fast (and how large) your mugo will grow.
Junipers as a genus are generally regarded as drought-tolerant and their wide distribution in the wild covers many arid areas. There are hundreds of juniper cultivars and almost all of the ones available in the trade can handle low-water conditions. Junipers have the added advantage of often being more reasonably priced than other genera; however, they do not command the respect of most other conifers, although ‘Blue Star’ is a highly praised, blue dwarf specimen.
Finally, once certain species have survived and flourished through several cycles of arid summers in the garden, the best chance of finding successful additions is to look for more species in that genus. The conifers that have been found most equipped to deal with drought conditions in Sonoma County are all members of the cypress and pine families. Within the Pinaceae family, Pinus itself is the most reliable genus. While there are a few firs and spruce that do extremely well in drought conditions, there are far more that would languish, if not die outright.
When considering drought-tolerant plants, it is important to keep in mind that nearly all must be provided with supplemental water, especially during the first two or three years after planting. Weekly waterings are usually needed, although in the hottest part of summer, twice a week may be necessary. A 3-4 inch layer of mulch vastly improves water retention. An added complication is that many drought-tolerant plants are from places with poor, rocky soil. In many areas of Sonoma county soil is clay-based and poorly draining, so it helps to add generous amounts of lava pebbles at planting time to facilitate drainage.
Most importantly, there is an enormous difference between the water needs of a newly planted conifer and one that has an established root system. When a conifer is drought-tolerant, that always means once established. It generally seems to require at least 2-3 years for dwarf conifers to develop large enough root systems to deal with less-than-ideal watering. Also, even for species that prefer full sun, providing a bit of afternoon shade helps their ability to conserve water and retain their good looks.
This article has been adapted from one that appeared in the journal of the American Conifer Society, the Conifer Quarterly. For more information about conifers, see www.conifersociety.org.