What's Wrong with my Blue Spruce?
Why are Blue Spruces so Popular?
Blue is generally a much-sought-after color in the garden, as is attested to by the abundance of flowers that have 'blue' in their names, despite clearly being shades of purple, lavender or mauve. So if so many flowers that are purported to be blue are not, how do you get real blue in your garden? Blue conifers, of course! Because in the world of conifers, when we say blue, we mean blue! The photo above contains two cultivars of Colorado spruce, also referred to as blue spruce, one of the bluest conifers out there. In the background, Picea pungens 'Fat Albert' draws the eye and provides soft, elegant contrast to the green foliage around it. In front, the cultivar 'Lucretia', has clear, powder-blue needles and a more random growth habit. Blue spruces have been popular primarily because of their color, although their stately, conical or columnar shape is attractive. However, blue spruce can often present problems when used in the home landscape.
Colorado (or Blue) Spruce in Nature
Colorado spruce, also referred to as blue spruce, is botanically styled Picea pungens. Picea is the genus name for spruce, and pungens, its species name, means 'sharp' or 'spiny' in Latin, which refers to the spikiness of the needles. (Read more about botanical terminology.)These trees, as their common name suggests, are native to the central and southern Rocky Mountains, a semi-arid steppe climate, where they occur in varying shades of greens and blues. The blue spruces that we know from home landscapes were selected for their blueness (more about that later). The blue coloring is due to a waxy substance on the leaf surface that protects the tree from desiccation and harmful UV light.The more wax, the bluer the needles. This waxy coating can be harmed by repeated touching (there is even anecdotal evidence that in very windy sites the trees lose their blueness), excessive rain or overhead irrigation, or by some pesticides and dormant oil sprays. Any of this disturbance to the wax can turn your blue tree to green. Blue spruce are extremely cold-hardy, able to withstand temperatures down to -40F/-35C, designated USDA zone 3.
The trees in nature can reach impressive heights; it is not uncommon to find individuals that are over 100' tall, with trunks 5' or so in diameter. It is a relatively slow-growing tree, as wild trees go, but it is long-lived (many reach 600-800 years). Picea pungens does best in cool climates with regular, short bursts of summer rainfall, conditions that are difficult to duplicate outside its native, mountainous, range. In habitat, it is more often than not found growing near streams, where the soil moisture is higher than the surrounding area. One source suggests that blue spruce require the same amount of water as Kentucky bluegrass!
Blue spruce is probably the most widely known, widely planted blue conifer in the United States. It is also likely responsible for most dislike of conifers! Why? Because species Colorado spruce trees were heavily planted in new residential communities in the early to mid-20th Century, and most, if not all, were planted with no regard for their ultimate size or whether they were climate-appropriate. While it may be an urban legend, it is said that a blue spruce in the 1930s and 1940s was a status symbol, widely proclaiming that the homeowner had 'arrived'! Even a 'slow growing' tree can outgrow its garden location!
This Colorado spruce was probably planted about the same time that the house was built. It was likely an adorable, size-appropriate landscape addition at the time. Seventy five years later, the house is still the same size, but the tree now towers over it, shading the interior all year long. The two cultivars (short for 'cultivated variety', a term used for plants that were selected by horticulturalists and growers for garden-worthy characteristics) shown in the first photo, grow MUCH more slowly and were selected for the intense blueness of their needles.
Homeowners don't just dislike blue spruces because they get too big, they dislike them because in many places that they were planted, especially the East coast and the Midwest, they have eventually performed poorly, succumbing to needle cast diseases and canker. Despite the widespread planting of blue spruce, they usually do not perform well over time in climates with humid summers, warm nights or inadequate rainfall or irrigation. Yes, you read that right. If you live in the Northeastern, Southeastern, Midwestern or Northwestern parts of the United States, despite the fact that blue spruce are ubiquitous, most eventually fall prey to disease and languish. Blue spruce is also commonly planted in northern Europe, where it suffers similar problems to those it experiences in the U.S.
Blue Spruce Diseases
By far the most common complaint of cultivated blue spruces is needle cast disease, mostly that caused by the fungus Rhizospaera kalkhoffii. It infects young needles and overwinters on living or recently killed foliage. During the growing season, the spores spread to other branches, or other trees, by splashing water. Warm temperatures (high 70's) exacerbate the needle infection. The disease generally presents as it does in the above photo, with the older needles dropping off first. There are other pathogens that can cause needles to die and drop off, but Rhizospaera is the most common, followed by Stigmina/Mycosphaerella.
Tip blights can also be a problem. Whereas needle cast can affect the older needles, tip blights are fungal diseases that cause dieback only to new growth. These kinds of blights are most common on pines but can affect spruces as well.
Finally, canker diseases are caused by yet another type of fungus that attacks the branches or the trunk of the tree. Cytospora is the most common canker pathogen.
These three fungal diseases were, for decades, the most common afflictions of blue spruce in the home landscape, but Michigan State University has identified two other fungal pathogens, Diplodia and Phomopsis, which are deemed secondary pathogens so the extent of their contribution to spruce death is unclear.
There are insects, too, that can cause damage to blue spruce, but it is the fungal pathogens that typically contribute to the poor cultural results observed on out-of-range species trees.
Unfortunately, despite the availability of pathogen-specific pesticides and oil sprays, once a tree is infected with a fungal disease it is very difficult to halt the decline, much less reverse it, even with dutiful spraying. Old, large trees planted in commercial spaces or in home gardens that were 'inherited' by new owners are generally left to make it on their own, with little supplemental care. This is one of the reasons that there are so many large blue spruce in decline in many parts of the Northeast, Midwest, Midatlantic and Southeast.
How to Grow Blue Spruce Successfully
To recap, blue spruce are only native to the mountain west, they generally occur at higher elevations, they prefer a cool climate with wet summers and are extremely susceptible to fungal diseases in cultivation outside of their native range. So what's a blue spruce fancier to do? And while there are certainly copious examples of poorly performing (or dead) blue spruces all over the United States (and Europe), there is also copious anecdotal evidence of spectacular successes. What is not clear is whether the successes are isolated to a few non-Rocky Mountain areas where the climate mimics that of the native range, whether they are just too young to have suffered the inevitable diseases, whether the particular cultivar in question is somewhat or completely disease-resistant, or whether the particular site or cultural practices worked in favor of the tree's health. Taking these one by one:
- Location. Obviously if you are in the native range, you should be able to grow Picea pungens successfully. Areas bordering on the native range are likely also to have climatic conditions conducive to success with this tree. The summer-dry Mediterranean climate of coastal California and Oregon also seems to produce long-lived, healthy landscape trees. If you are outside of these areas, careful cultural practices will improve your chances of success. There are ample examples of healthy, decades-old blue spruce in the Midwest and the Northeast and even in parts of the Southeast.
- Age. Unless you are the steward of a family estate or the curator of a public garden or other public space, it is unrealistic to think in terms of centuries when planning your garden. You have no control over what happens after you move or die; the next owner may chop the trees down and put in a swimming pool. So for most of us, it is logical to think in terms of a few decades at most. Thus, even if disease is going to get the tree in the end, but you can enjoy a few decades with it, that may not be a good enough reason to avoid a blue spruce. Dennis Groh notes that from what he has read, "the species spruce are disease resistant when they are young and growing vigorously. It seems that at about 25 years something happens and the spruce become highly susceptible. One article speculated it could something to do with the tree's inability to move adequate water to all parts of the tree and a resulting inability to then defend against disease attack. Another speculated the tree at some point exhausts all available elements in its rather limited root zone and requires supplemental fertilization to support its rapid upward growth and maintain its defense against disease. I have seen the root system on 70 foot spruce and it is much smaller than I would have expected based on deciduous trees."
- Disease-resistant cultivars. This is the most difficult factor to assess. There is no hard evidence that Picea pungens cultivars in general, or any specific cultivars, are more resistant to disease than the species trees. While most of the examples of success are, indeed, cultivars, that could well be due to the fact that most conifer enthusiasts plant cultivars, not species trees; that the cultivars are newer to the market, thus younger and not yet affected with disease; or that more care has been taken with the cultivars as they are generally thought to be more 'special' and are certainly more expensive than the species. (What's the difference between a species and a cultivar?) It should go without saying that choosing a cultivar with a slower growth rate than the species is also a good idea, unless you are landscaping vast parkland.
- Cultural practices. This is key. If you have decided, despite the issues, to plant a blue spruce, your best chance of success is to plant and care for it properly.
Evaluate your Climate for Blue Spruce Success
- In the Mountain West or near it, you can grow blue spruce successfully.
- In Mediterranean climates from Central California through Oregon, blue spruce tends to do well, although it may require supplemental irrigation. The cool summer nights and dry summer air are similar to those in the tree's native range. Established trees seem to be more drought-tolerant.
- In the upper Pacific Northwest, the weather tends to be too wet and fungal pathogens are too numerous. Another choice would likely be better to ensure long term success. Blue spruce is extensively produced in Oregon, where growers focus on using disease-resistant stock, avoiding overhead watering and avoiding pruning when the foliage is wet.
- In the upper Midwest and Northeast, blue spruce have been extensively planted and there are almost as many success stories as there are those of decline and death. This is where cultural practices may make a significant difference. Longevity (or lack thereof...), cultivar selection and luck may also have had a hand in the results! It is worth noting that one of the most popular blue spruce cultivars, 'St Mary' (also called 'St. Mary's Broom') not only has anecdotal evidence of success in the Northeast, but was actually found on a tree growing in Morristown, NJ.
- In the lower Midwest, according to Edward Gilman, professor emeritus of horticulture at the University of Florida, blue spruce 'is not for Dallas and south Texas, but Lubbock and into Oklahoma is suitable'.
- In most of the American Southeast, you will likely want to select a different conifer than a blue spruce. Tom Cox, who, with John Ruter, wrote 'Landscaping with Conifers and Ginkgo for the Southeast', firmly believes that summer nighttime temperatures regularly have to dip below 70 degrees F by 10:00 pm in order for blue spruce to be successful. In addition, he suggests that the heavy summer rainfall in much of the Southeast tends to dissolve the waxy coating that gives the blue spruce its blueness, making them a dull green instead of an arresting blue. In fact, he says that if he were to revise the book, he would not recommend Picea pungens for any parts of the Southeast, with the exception of higher elevations, such as Asheville, NC. Those that do survive, he notes, are not particularly attractive.
- In the few parts of the US that are tropical, you will also have to find your garden blue elsewhere, but there are conifers for you, too!
Which Blue Spruce Should I Plant?
For long-term satisfaction with your blue spruce, select a cultivar, not a species tree. A species, or wild, tree will simply be labeled 'Picea pungens'. Cultivars, selected for particularly attractive features or growth habits, always have a 'third' name on the label, e.g. Picea pungens 'Pendula'. The cultivar name may reveal something about the tree's growth pattern, as well as identify it as a selection. 'Pendula' is a weeping form, whereas 'Fat Albert', not surprisingly, has a wide shape. 'Glauca Procumbens' creeps along the ground. Cultivars will almost always grow significantly more slowly than their wild cousins and do not reach such massive proportions.
It is the slower growth rate and wide range of growth habits that make cultivars better choices than species trees for home landscapes. That photo of the species tree towering over the house would look very different if, instead, the homeowner or builder had planted a Picea pungens 'Hoopsii', which grows at about half the rate of the species. (Bonus: 'Hoopsii' is viewed as one of the very bluest by many conifer enthusiasts!)
You want to begin by evaluating the spot where you want to plant your Colorado spruce. How much space does it afford? Cultivars of this tree range from very small and slow-growing to those that grow at about half the rate of the wild trees. Some are intensely apically dominant with a pronounced excurrent form (A tree with a straight trunk that goes from the ground all the way to the tip; classic 'Christmas tree' shape.) Others scramble along the ground, weep, or are sedate bun-shapes. So, the first question to ask yourself is, where do I want my blue and what shape and general size should it be?
Note that the more irregular forms of blue spruce (and any conifer) are easier to keep pruned to a desirable size, as they do not present the problem of having to cut off the top and destroying the conical shape. And many cultivars, such as the one pictured above, form no leader at all and remain cushion or bun-shaped for their entire lives.
Finally, many cultivars have been selected for the intensity of their blue color. So if blue is your goal, review comments about the different cultivars and select accordingly.
Coming soon: The 10 Best Blue Spruce Cultivars
How to Plant and Care for a Blue Spruce
As noted above, cultural practices are likely the most important controllable factor in whether or not your blue spruce not only survives, but flourishes. So let's assume that you are in a climate where needle cast diseases are prevalent, but you see local examples of attractive Colorado spruce and you want to try your luck. If you are in a climate where they are native, or a climate with similar attributes, it doesn't hurt to bear these practices in mind, either. Rhizosphaera needle cast is much more likely to be a problem with trees that are already in a stressed condition due to poor growing conditions.
- Blue spruce prefer acidic, moist, well-draining soils. If your soil is heavy and poorly draining, or is basic, plant in mounds of high quality soil with grit, pumice or pebbles added to increase drainage. DO NOT dig a hole and backfill with non-native soil. This creates a bathtub effect whereby the hole, with looser, lighter soil, simply fills with water during rain or irrigation.
- Plant your blue spruce so that the beginning of the root flare is evident. This is good practice for almost all woody plants, but with those that need good drainage it is particularly important.
- Blue spruce should always be planted in full sun.
- Maintain good air circulation around the plant. This means not overcrowding the plants in the bed or area. Remember to consider the tree's mature size when planning! If lower limbs are touching the ground, remove the entire limb or prune the underside or tips to lift the skirt so that it clears the ground.
- Pruning is fine; in fact, pruning to open the architecture and increase air flow is likely a positive. However, avoid shearing, as shearing produces dense, congested growth that holds water longer than the tree's natural foliage. There is anecdotal evidence that keeping the foliage as open as possible is helpful, which means getting inside and removing dead or unattractive branches and allowing the air and sunlight to reach as many needles as possible.
- Spread and maintain a layer of mulch covering the root zone of the tree (roughly to the edge of the branches) of several inches. This will keep the soil moister and cooler and reduce weed growth. Do not mulch up to the trunk; leave an inch or two so that the damp mulch is not piled up against the trunk.
- As noted above, blue spruce grow best in their native habitat when they are near streams and lakes. Make sure that your tree gets enough water, especially when young. Older trees may be more drought-resistant, but still need supplemental irrigation at times of scarce rainfall. Extended periods of drought can weaken the trees and make them more susceptible to pathogens.
- If you are in a summer dry climate, or in the mountain west, you can use overhead irrigation in summer, as the water evaporates quickly from the needles. If you are in most of the US or Europe, you should water using drip irrigation or a hose at the base of the tree. Avoid getting water on the needles, as the moisture promotes fungal growth and transmission.
- Fertilizing is not necessary when the tree is young, however, as Dennis Groh notes, "The key is to keep the tree well watered, fertilized, healthy and growing." So after its been in the ground for a few years, regular fertilizing is a good idea.
- If your tree does exhibit evidence of needle cast disease, you should seek confirmation of the specific pathogen before applying fungicide. Most county extension offices can review samples of infected foliage and provide a diagnosis. You can also search on line for examples of needle cast disease and compare with your plant. Different pathogens require different fungicides, so don't start spraying indiscriminately!
What to Plant instead of a Blue Spruce?
While blue spruce cultivars are the most widely-planted blue conifers, that doesn't make them the only, or even the best, choices. Depending on where you live, you may have several attractive alternatives. Photos are in the gallery at the end of the article.
Abies concolor cultivars (USDA zone 4). Abies concolor, or white fir, Colorado white fir or Rocky Mountain white fir, is native to roughly the same area as Colorado spruce, but also to large sections of California, New Mexico and Arizona, even venturing into Baja California and Sonora. It is a fir, not a spruce, but its growth habits and appearance are not dissimilar to Picea pungens. As the photo above demonstrates, many of the cultivars are a striking, saturated blue. White fir has shown to be successful in the upper Midwest (the photo above is from a garden in Michigan) and Gilman recommends it for cultivation in the lower Midwest as well. It has been observed growing successfully in the Northeastern US as well. If you can grow it, this is likely one of your best choices, ,if not the best, for powder-blue foliage.
Abies koreana cultivars (USDA zone 5). Korean fir comes from high-elevation areas in Korea, that have temperate rainforest with high rainfall and cool, humid summers. Many cultivars, such as 'Blue Magic', have blue or blue-green needles, but they are not the light, powdery blue of blue spruce.
Abies lasiocarpa cultivars (USDA zone 5). This species is known as sub-alpine fir as well as a host of other common names and is native to Western Canada and the Pacific Northwest, extending into the Rocky Mountain states. Those that are styled Abies lasiocarpa var. arizonica have very glaucous, or blue, foliage. These cultivars have proved to be very successful in the upper Midwest.
Abies procera cultivars (USDA zone 5). This species, called noble fir, is native to the Cascade and Coast Ranges in CA, OR and WA. Some of the cultivars are very blue, and it has been grown successfully in Mediterranean CA and the upper Midwest. 'Glauca' is an elegant selection, 'Blaue Hexe' has powdery blue needles, and 'Glauca Prostrata' is a spreading form with silvery blue foliage.
Cedrus atlantica cultivars (USDA zone 6). Cedrus, the genus of true cedars, is hardy only to USDA zone 6, so if you are in a colder zone you will have to give this one a pass. The cultivars 'Glauca Pendula' and 'Sapphire Nymph' are very blue, as is 'Blue Cascade' and 'Horstmann'. These cultivars vary enormously in their growth habits so check photos and descriptions before you make your selection. Tom Cox suggests Cedrus atlantica cultivars as good substitute for blue spruce in the Southeastern United States. Michael Larson, who gardens in central Pennsylvania, also uses Atlantic cedars in lieu of blue spruce. Dan Spear weighs in from Asheville, NC, with a thumbs up for 'Sapphire Nymph'. Some of these blues are very close in hue and tone to those of blue spruce.
Cedrus deodara cultivars (USDA zone 6) Deodar cedars have longer and softer needles than Atlantic cedars, and their blues tend to be deeper-hued. Try 'Prostrate Beauty' for a low, wide-growing plant, or 'Devinely Blue' for one that will eventually form a leader and grow into a tree. Robin Tower has a magnificent specimen of 'Devinely Blue' in her garden in North Carolina and Tom Cox also reports success further south in Georgia.
Blue Cypress and False Cypress:
Chamaecyparis lawsoniana cultivars (USDA zone 6). This species of false cypress is native to coastal Oregon. Some of the cultivars, notably 'Pelt's Blue' and 'Pembury Blue' are strikingly colored and as dramatic in the landscape as blue spruce. Note: Lawson's cypress is extremely susceptible to water mold infections caused by the soil-borne pathogen, Phytophthora . Most growers are now using disease-resistant rootstock, which eliminates the problem. ONLY buy C. lawsoniana if it is grafted onto DR rootstock.
Cupressus glabra cultivars (USDA zone 7). Cupressus glabra, or Arizona cypress, has several eye-catching icy blue cultivars. Arizona cypress is native to the American and Mexican Southwest. Some of the bluest cultivars are 'Carolina Sapphire', 'Blue Spire' and 'Blue Ice'. Most of these become fairly good-sized trees, and are not as formal and regular as blue spruce, but the colors are dramatic.
Juniperus squamata cultivars (USDA zone 4). Probably the most dramatically blue is 'Blue Star', which is a low, mounding plant that does well in most of the US.This one benefits from more water than most junipers, with members in England and the Upper Midwest reporting that frequent summer irrigation is key to the plant thriving. 'Blue Carpet' is even more low-growing than 'Blue Star' but not as intensely blue.
Juniperus conferta cultivars (USDA zone 5). All J. conferta cultivars are tolerant of wind, shade adn salt spray, making them suitable for many spots where other plants cannot survive. 'Blue Pacific' has a low habit and soft, feathery foliage. Its needles are longer and softer than many other junipers and people who turn their nose up at junipers (more on that in a different article!) often really like this one. 'Blue Lagoon' is another nice choice.
Juniperus scopulorum cultivars (USDA zone 3). This species, commonly called Rocky Mountain juniper, is about as cold-hardy as you will find among the blue conifers. 'Wichita Blue' is a conical selection that is rated 'intermediate growth rate'.
Juniperus horizontalis cultivars (USDA zone 4). This species is known as creeping juniper and some of the best low-growing blue conifers may be found here. 'Blue Chip' is a robust, very blue groundcover that makes a lovely blue skirt around a contrasting colored tree. 'Blue Rug' is another and 'Pancake' is probably the lowest growing juniper of them all!
Juniperus virginiana cultivars (USDA zone 4). Confusingly known as Eastern red cedar, this species has a large range, covering the southeastern US, the Midwest and venturing into Canada. Some cultivars, such as 'Royo' have a distinctly blue cast to their needles. Blue Flame is a particularly blue selection. For those of you in the Southeast, Tom Cox advises that 'Royo' is at the top of his list of blue conifers for both longevity and form.
Pinus koraiensis cultivars (USDA zone 3). These are very cold-hardy choices with a variety of growth habits. 'Morris Blue' is upright, with silvery blue-green needles. 'Blue Ball' is a spherical dwarf, and 'Compacta Glauca' is a semi-dwarf conical shape. None of these cultivars will look much like blue spruce; they are darker colored and much greener blue. However, they do have a bluish cast and make attractive accents when planted with green-foliaged plants.
Pinus kwantungensis (USDA zone 9), another Asian pine, has a bluish cast and is an attractive choice if you live in a mild climate and have room for a species tree. It's much less common than most of the other species covered in this article, but deemed a winner in both Mediterranean Northern California and the Southeast.
Pinus strobus cultivars (USDA zone 3). Similar to Korean pines, these Eastern white pine cultivars are very cold-hardy, with good adaptability to warmer climates such as the Southeast. They, also, have dark needles that are not very similar in color to blue spruce, but can provide some bluer hues to a green landscape. Consider 'Blue Shag' or 'Blue Clovers' for the bluest strobus; there are other cultivars that have a blue cast to their needles. Tom Cox notes that 'Blue Clovers' has been the superior performer in the Southeast.
Pinus parviflora cultivars (USDA zone 5). These Japanese white pines are lovely, graceful trees with a more delicate structure and appearance than many other Pinus species. 'Aoi' is a nicely formed blue selection, 'Blauer Engel' is probably the lightest blue parviflora, and 'Glauca' has silvery-blue needles. There are many cultivars to choose from. In the Southeast, Tom Cox recommends that you site these where they receive some shade, where they will do well and hold their blue color. He also likes 'Blauer Engel'.
Pinus peuce 'Pacific Blue' (USDA zone 4). This cultivar of Pinus peuce, a species commonly called Macedonian pine, stands out as one of the best blue pines of all. Dan Spear, near Asheville, NC, notes that his 'Pacific Blue' is planted next to a Pinus parviflora 'Blue Angel', and it makes the 'Blue Angel' look medium green!
Podocarpus elongata cultivars.These are for those of you in tropical or semi-tropical climates, as this species is rated zone 9 minimum and does very nicely in zone 10. Try 'Monmal' (Icee Blue) or 'Blue Chips' for some serious blue action!
Blue Spruces OTHER than Picea pungens
Picea engelmanii cultivars (USDA zone 3). These can get fairly large and they are not as strikingly blue as blue spruce, but they are reliable performers in colder areas of the US and Europe. Try 'Blue Harbor', 'Bush's Lace' or 'Blue Magoo'. Note that Engelmann's spruce is also susceptible to needle cast disease.
Picea asperata cultivars (USDA zone 6). 'China Blue' is about as close to looking like a blue spruce as you are going to find. Dragon spruce, as it is commonly called, is nowhere near as prevalent in the trade as blue spruce, and there is not as much information about how it performs in cultivation. If you do come across it, it is worth a try.
Have information or experience with particular 'blue spruce alternatives'? Comment below or email firstname.lastname@example.org. We'd like to hear from you!
Click on any photo in the gallery for more information:
Thank you for the information. Very helpful.
You are most welcome, Susan!
Excellent article! Which alternants would you consider deer resistant?
We don't opine on deer resistance because it is so variable. My own experience is that if they get hungry enough, they'll eat almost anything, and deer problems are not restricted to browsing; male deer can destroy a tree with their antlers. Your best bet is to check with neighbors/local nurseries to get some local anecdotes.
Once the waxy covering causing the blue color on Fat Albert has been dissolved, will it come back?
no. It's gone forever until next spring when you get new needles with new wax.