Drought-Resistant Conifers

By Sara Malone

Discover low-water conifers for the Western region, and beyond.

The conifer, Siberian cypress (Microbiota decussata) in winter color
The conifer, Siberian cypress (Microbiota decussata) in winter color

What thrives in New England languishes in Georgia, and what over-winters happily in California succumbs to brutal Minnesota ice and snow. Like those of taxonomy, regional distinctions can be “split” or “lumped”, and by creating only four regions, we are in the lumper’s camp!

The USDA makes more distinction, with 10 zones based on average low winter temperatures. However, those of us who garden know that there are many times when we feel as if our garden is in a zone of its own.

The Western Region is not only the largest ACS region geographically, but also has the greatest range of climatic conditions, from the tropical Hawaii to the Rocky Mountain states of Colorado and Wyoming; from the deserts of Arizona and New Mexico to the rain forests of Western Washington. We clearly can’t all plant the same conifers and have them flourish, but we do look for similarities in conditions and try our best to understand the needs of each genus to try to make the best choices for our gardens.

Growing Regions and Droughts

While the West has a wide variety of climates, we do share a few common attributes. Most of the West, for example, enjoys much cooler summer nights than the states east of us. No matter how hot we get during the day, we can almost always count on the heat mitigating significantly once the sun goes down.

We also tend to have much drier summer air than the eastern two-thirds of the country. The cooler nights make it easier for many of us here to grow conifers which struggle in the South. The drier summer air means that those conifers native to places with warm weather humidity don’t do as well here as they do in Georgia. But all of the various climatic attributes which have occupied our collective Western consciousness when selecting plants have coalesced over the last couple of years into one: drought.

The conifer, Juniperus horizontalis ‘Blue Chip’
The conifer, Juniperus horizontalis ‘Blue Chip’

Adapting to Droughts and Other Conifer-Growing Conditions

And, it’s not just California; even the Pacific Northwest, the land of ‘liquid sunshine’ (as they cheerfully refer to rain), has seen lower-than-usual snowpack in Washington and severe drought ratings in Oregon. The Smithsonian Magazine reports that Arizona could be out of water in six years and scientists at UC Irvine and NASA recently completed a study which suggests that the groundwater reserves in the Colorado River Basin are being depleted at a rapid rate.

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 suitable for the climate and setting. For much of the West, that means selecting plants which can withstand our lower water situation. While I will specifically discuss my own garden conditions, it is a simple matter to follow the same thought-process for your own climate, whether the prevailing adverse condition be drought, warm summer nights, or low winter temperatures.

Advantages of Conifer Cultivation in Harsh Conditions

Conifer lovers are fortunate, because compared to many other kinds of plants, in general, evergreen conifers are well prepared to deal with adverse conditions. These ancient plants evolved during a time of great climatic change in the world and consequently have dealt with conditions far more extreme than we are facing today.

They are wind-pollinated, hence are not affected by any asynchronicity between themselves and insects which might arise from drought or temperature fluctuations. They also can conserve nutrients by not being forced to produce a full, new set of leaves every year. They can photosynthesize if conditions are harsh and prevent—or delay—new growth.

Because they are always “in leaf ”, they can photosynthesize whenever conditions are right—they don’t have to wait for bud break. This also means that they can take advantage of irregular rainfall, even if it is outside of the normal growing season. It is interesting to note that conifers dominate in the mild climate of the Pacific Northwest—most other places dominated by conifers have much harsher climates (e.g. boreal forests). Why would that be?

The answer seems to be the modified Mediterranean climate of the PNW, which while it has mild, wet winters, also has mild but dry summers. The evergreens can produce food during the mild winters, when deciduous trees are bare and ineffective, and the summer dryness is hard on deciduous species, which can’t compensate by photosynthesizing in the other three seasons.

The drought-resistant Ginkgo biloba, in fall color
The drought-resistant Ginkgo biloba, in fall color

Dry Summers in The Coastal West

In fact, much of the coastal West enjoys a Mediterranean, or modified Mediterranean, climate. That means wet winters and dry summers, with much of our weather directly influenced by the Pacific Ocean. The conifers we plant in our gardens generally receive supplemental irrigation, but we cannot replicate humid summers with reliable rainfall.

With water a scarce commodity, most of us use drip irrigation, which does not humidify the air at all. The readings on the hygrometer at my house are in the 30-40% range from June-September. So, where do we go to find conifers which will not just survive, but flourish in this kind of summer-dry environment, especially when drought is always on our minds?

Going Native with Conifers

The first place to look, when seeking conifers which will do well in our gardens, is in our own native plant population. These conifers, such as Pinus contorta, Pinus ponderosa, Sequoia sempervirens, Pseudotsuga menziesii and Cupressus macrocarpa, have evolved to deal with the specific conditions of the area, so should work best in our gardens, right?

In California alone there are over 50 native conifers, about half of which have more garden-appropriate cultivars. Some of the darlings of the conifer aficionado’s collection are amongst these plants: Pinus contorta ‘Chief Joseph’ and ‘Taylor’s Sunburst’ and Picea engelmannii ‘Bush’s Lace’ and ‘Blue Harbor’. Where it gets tricky is that California is a big state, with coastal, mountainous and desert regions.

Sequoia sempervirens, for example, are only truly happy in a narrow band practically within sight of the Pacific, and Picea engelmannii prefer the moist slopes of the Klamath Ranges. I grow cultivars of all of these species here in my garden, but I wouldn’t classify them as “low water” conifers.

The Right Conifer for the Right Conditions

Going native sounds good, but doesn’t always produce the best choices. In addition, of garden-worthy note is Pinus ponderosa, which has several cultivars. Ponderosa pine has a long tap root, which makes it able to reach water sources. It needles, like those of Sequoia, absorb the gentle moisture from fog.

When seeking natives, focus on those which can handle the specific extreme, to which you will be subjecting them. Cupressus macrocarpa, for example, withstand low rainfall, poor soils and Pacific gales, so is an appropriate California native conifer for low-water situations.

The ‘Lone Cypress’ of the Pebble Beach golf course is a Cupressus macrocarpa and is said to be one of the most photographed trees in North America. It is estimated to be 250 years old and has survived not just wind and low rainfall but fire. Now there is a tough plant! The garden cultivars are lovely, with ‘Coneybearii Aurea’ and ‘Greenstead Magnificent’ among my very favorite of all of my conifers.

The conifer, Cupressus macrocarpa ‘Coneybearii Aurea’
The conifer, Cupressus macrocarpa ‘Coneybearii Aurea’

Taking Conifers to Extreme Measures

Even better than many of our natives, the conifers which truly seem to deal with the dry summers and extended periods between waterings are those which are native to regions with extreme conditions. The Mediterranean conifers, for example, are the best equipped to handle less-frequent waterings.

Abies pinsapo (with some great cultivars such as ‘Horstmann’, ‘Glauca’ and ‘Aurea’) and cultivars of some of the cedars, such as Cedrus libani and Cedrus atlantica, are standout performers in my garden, and once established, can handle much less-frequent waterings than Sequoia sempervirens. There is a wide range of size, color and form amongst the cedar cultivars; thus, you can have quite a bit 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. Picea pungens, which are native to the Rocky Mountains, are prized for their intense blue color. That color results from wax on the needles which is believed to reduce their temperature, as well as transpiration and light absorption. That protective wax helps Colorado blue spruces retain moisture and deal with low-water conditions. Once established, Picea pungens cultivars are some of the summer-hardiest conifers in my garden.

Pinus mugo: A Tough Mountain Conifer

Pinus mugo hail 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 that, if you select one of these, you will avoid the dreaded guessing game of wondering how fast (and how large) your mugo will grow.

Conifer Focus: Junipers

Junipers as a genus are generally regarded as drought-tolerant and their wide distribution in the wild covers many arid areas. We have native Juniperus in rocky, dry areas in California, and there are others endemic to the Mediterranean, North Africa and other desert or quasi-desert locations. 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; they do not command the respect of Abies koreana or Pinus parviflora! When I fell in love with a large Juniperus cedrus at a wholesale nursery and was astounded to hear how inexpensive it was, the owner explained: “It’s a juniper—no one will pay up for it.”) Likewise, Ginkgo biloba (while not a conifer, is a gymnosperm and under the ACS umbrella) is drought-tolerant and withstands poor conditions.

Keep it in the Family

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. It is not a coincidence that the list of conifers, which I have found most equipped to deal with drought conditions, are all members of the cypress and pine families (other than Ginkgo, which is, as usual, an exception!)

Within Pinaceae, certain genera are much more widely represented, with Pinus itself the most frequently occurring genus. While there are a few firs and spruce which do extremely well in drought conditions, there are far more which would languish, if not die outright. The cypress family representatives are all in the subfamily Cupressoideae.

It’s interesting that the members of this subfamily are native to the Western United States, with the exception of Microbiota decussata, or Siberian cypress, which, as its common name implies, is native to the mountainous region of southeastern Siberia. Even though it calls home a spot far from the rest of its subfamily, its morphology puts it amongst them and it shares with them the ability to endure drought.

The conifer, Juniperus squamata ‘Blue Star’
The conifer, Juniperus squamata ‘Blue Star’

Actual Garden Drought Conditions

When I speak of drought-tolerant plants or gardening in a low-water environment, I do not mean to suggest that I provide no supplemen-tal water. Northern California generally only has rainfall between November and April. We had no rain at all between late December 2012 and December 2013.

An added complication is that many drought-tolerant plants are from places with poor, rocky soil. My local soil is clay-based and heavy (a mile away is General Vallejo’s Petaluma Adobe, the largest adobe building remaining in the United States, built in the mid-nineteenth century from adobe bricks made at the site). The clay is water-retentive and poorly draining.

Therefore, I add generous amounts of lava pebbles to increase drainage. Amending soil to accommodate plants which are native to other parts of the country or the world is a subject for a separate discussion; suffice it to say that it is as important as far less water than overhead spray and also reduces weeds.

Different Conifer Watering Needs

Most parts of the garden are watered weekly, although in the hottest part of summer I water twice a week. I use a 3”– 4” layer of mulch, which vastly improves water retention. For those of you in areas which generally enjoy summer rain, but have had—or fear—drought conditions, some of the plants on my list will work in your climate as well. You can also use the same rationale for making a list of those best suited to your zone, humidity, and so forth.

Most importantly, there is an enormous difference between the water needs of a newly planted conifer and one with an established root system. When I say that a conifer is drought-tolerant, that always means once established. It generally seems to require at least 2–3 years for conifers to develop large enough root systems to deal with less-than-ideal watering.

Also, even for species which prefer full sun, providing a bit of afternoon shade helps their ability to conserve water and retain their good looks. I do water overhead 1–2 times per summer to provide a good soaking and flush off dust. Really established mature conifer trees can get by with much less than a weekly watering. The Sequoia sempervirens, which were planted by our predecessor and are over 40’ tall, for example, get no supplemental water at all, and they are further inland than their ideal situation. I water full sized trees once a month at most.

Best Low-Water Conifers

These are the best drought-resistant conifers, from my own experience. All have cultivars available in the trade:

Sources: ACS ConiferBase, Centralia College lecture, Aris G. Auders and Derek P. Spicer, RHS Encyclopedia of Conifers

Photographs by Janice M. LeCocq.

This article was originally published in the Fall 2014 issue of Conifer Quarterly. Join the American Conifer Society to access our extensive library of conifer-related articles and connect to a nationwide group of plant lovers! Become a member for only $40 a year and get discounts with our growing list of participating nurseries in our Nursery Discount Program.