Tall and stately, one of the most beautiful evergreens is Colorado blue spruce. A native of the Rockies in Western America, it has become widely dispersed as an ornamental tree, adorning gardens and parks all over Canada and the United States. It is hardy in zones 2 to 7.
The Colorado blue spruce ( Picea pungens) has silvery blue needles and a lovely pyramidal shape. It grows from 50 to 75 feet in a city garden and can spread 10 to 20 feet – even beyond, if it’s perfectly happy. A moderately slow grower, its strong leader takes it up 12 to 24 inches each year if it is in full sun. Near its crown in the upper branches, light brown cones hang down three to four inches and are much beloved by squirrels. To keep blue spruce free of its troublesome pests – adelgas gall mites, spruce bud worm, spider mite and pine needle scale – spray the tree with a water hose two or three times a summer. This will help to dislodge any of the sheltering beasts before they become too comfortable in the tree. Keep an eye out for any sooty mold and clean the branches of this infection as you work. The hose will remove some of the powdery white coating on the needles, which gives the tree its blue cast, but it’s worth doing to keep the tree healthy. The new needles that are produced at branch tips each year will bring back that blue glow.
Blue spruce also becomes host to needle cast diseases, which are most troublesome in cool, wet weather. There are two different types and both are fungal diseases that manifest in little black dots, replacing the white stomata (breathing vessels) on the underside of the needles. The tree will begin to turn a brownish-purple and then the older leaves will begin to die and drop. Treat with fungicide before the disease takes over and be sure to keep your tree well fertilized and properly hydrated so that it can fight off any infections before they get too serious.
If treated on time and for two or three years, your beautiful blue spruce can regain its good looks so it is well worth the trouble of treating it.
It should be noted that blue spruce lose their older needles every four to ten years from the branches nearest the trunk. New growth appears at the tips. Stress can accelerate this process. If the loss seems overly rapid, check for spider mite. Hold a sheet of white paper under a branch, shake vigorously, then smear your hand across the page. If red streaks appear, it is spider mite. Turn on that hose.
Fortunately, deer are not attracted to blue spruce, thanks to the inch-and-ahalf-long, sharp and strongly scented needles.
Use in the landscape
While a lone blue spruce makes a lovely statement of its own, remember that this magnificent tree needs a fair amount of space so be sure your yard is large enough to handle it.
It can also be used as an effective windbreak or hedge on a large property. Plant the trees 10 to 12 feet apart so that the adult tree branches will mingle with those of its neighbour.
There is also a columnar blue spruce, ( Picea pungens ‘Fastigata’) that grows in a cigar shape and adds six to 12 inches a year in height, eventually reaching 15 to 25 feet with a spread of three to six feet. The foliage is steel blue and it keeps its tidy shape without need for pruning. It can also be used to make a hedge. There are weeping, prostrate and dwarf forms of this blue tree as well.
A blue spruce can make an emphatic statement if planted in a grouping of trees with contrasting leaf colours – purple leafed cherries or autumn blazing Amur maple. Just remember how big they get.
Keeping your blue spruce blue
The blue cast on the needles is actually from a powdery looking, waxy substance that coats them, helping to keep moisture in the needles. To keep the colour, avoid exposing the tree to abrasive winds or other conditions that will affect the coating. Water your tree at the soil line and fertilize with a fertilizer created for acid loving plants in spring – not past July 15. Make sure the tree gets enough sunlight – at least six hours a day. Slow down watering in August and September then water well in October.
You can expect some darkening of the leaves in winter. The blue tone will return in springtime.
The silvery blue needles of the Blue Spruce.
Spruce tip blight blue-green-yellow rust transitions.