Colorado blue spruces, resplendent with silver-blue-green needles, are coniferous evergreen trees that are members of the pine family. The official state tree of Colorado, these spruces are native to Rocky Mountain states in the U.S. They were first discovered in 1862 growing on the Rocky Mountains, but are now one of the most widely planted landscape trees.
The Colorado Blue Spruce's silvery-blue needles are prickly to the touch and have a strong, fresh, piney smell. Its pyramidal shape, foliage color, and wonderful smell make this plant a classic choice for a Christmas tree. Not only are these spruces popular as Christmas trees, but their boughs are also useful in various kinds of Christmas decorations using greenery. From wreaths to swags to holiday garlands, lovers of tasteful Christmas yard decorations turn to boughs from evergreens such as Picea pungens for raw material for crafts projects. Some people even lay the cut boughs over a shrub shelter to provide "roofing" that will help the protected bush make it through the winter in good shape.
The best time to plant a Colorado blue spruce tree depends on the climate where you live. In mild climates, the trees can be planted throughout most of the year. If you live in an area with harsh winters and frosts, however, plant in late winter or early spring, February through March or April, while the tree is dormant. If necessary, you can plant a tree in early fall, but those planted in late fall won't have time to get established and are susceptible to winter injury and die-back.
Colorado blue spruces have a slow to medium growth rate. You can expect a height increase of less than 12 inches to 24 inches annually.
|Botanical Name||Picea pungens|
|Common Name||Blue Spruce, Green Spruce, White Spruce, Colorado Spruce, Colorado Blue Spruce|
|Plant Type||Spruce tree|
|Mature Size||In the wild, it can grow up to 75 feet. In parks and gardens, it typically grows 30 to 60 feet high and 15 to 20 feet wide.|
|Sun Exposure||Full sun|
|Soil Type||Acidic; loamy; moist; rich; sandy; well-drained; clay|
|Soil pH||6.0 to 7.5|
|Bloom Time||Year-round growth; no flowers|
|Flower Color||No flowers; silvery-blue needles|
|Hardiness Zones||2 to 7|
|Native Areas||From northern New Mexico through Colorado and Utah to Wyoming and into Alberta and British Columbia|
Colorado Blue Spruce Tree Care
Colorado blue spruce trees can be planted in rows to form windbreaks or "living-wall" privacy screens, but they are equally effective when simply used ornamentally as specimen trees. They're valuable in deer country, as their prickly texture and strong smell render them conveniently deer-resistant. In the snowy North, where landscapes can look barren in winter, evergreens such as Colorado blue spruce trees can provide much-needed winter interest.
To plant a Colorado blue spruce, dig a hole that is as deep and two to three times as wide as the root ball of the tree. Next, place the tree in the hole, so that the top of the root ball is even with the surrounding soil. Fill the hole halfway with soil or add compost, if the soil is poor, then water the soil to remove air pockets. Finish filling the hole, then water again.
Plant Colorado blue spruce trees in full sun, ensuring they get at least 6 hours of unfiltered sun per day.
These trees do best in a location with a moist, well-drained soil made fertile through the use of soil amendments. However, the trees can adapt to a variety of soils, whether acidic, loamy, sandy, or clay. When it comes to soil pH, these trees prefer a range between 6.0 and 7.5, but they're able to tolerate extremely acidic or alkaline soils.
Once established, this tree is drought-tolerant and can survive in periods of low water, but it does thrive with moderate water levels. During the first season, water the tree regularly to keep the soil moist. Once the tree is established, water only during dry spells. Avoid waterlogging the tree or creating areas with standing water.
Temperature and Humidity
The Colorado blue spruce is tolerant of cold weather. It can tolerate heat to a point. However, it will not thrive in extremely hot and humid weather conditions.
These trees do not need frequent fertilization. You can fertilize them in the spring, before the growing season, to give the tree an added nutrition boost. It will likely increase the length of the needles and improve the needle color. Sprinkle 10-10-10 slow-release granulated fertilizer over the soil in the root zone, and hen water with about 2 inches of water to prevent fertilizer burn and incorporate the fertilizer into the water.
Potting and Repotting
A growing trend is to buy Colorado blue spruce trees in containers for indoor Christmas decorating, then plant them outside as landscape plants after the holiday. Dig the hole in the ground for planting well before December, so you will not have to dig through frozen dirt. Bring the excavated dirt inside, to keep it from freezing. This will help to keep it loose so that you will have workable dirt with which to fill in around the new specimen after transplanting it into its hole.
However, remember that your tree needs to adapt to an entirely new environment when you transplant it into the garden. It's been inside, in a warm, sheltered space. Make sure to slowly transition the tree to cooler temperatures before you plant it outside. It may be best to wait until spring to transplant.
If you want to keep your spruce in a container for longer than a holiday season, choose a pot that's 12 to 16 inches wider than the root ball of the tree.
Types of Colorado Blue Spruce Trees
- P. pungens 'Baby Blue Eyes': Semi-dwarf cultivar that grows 15 to 20 feet tall
- P. pungens 'Bakeri': Features a deeper blue color and crows 12 to 20 feet high
- P. pungens 'Glauca Globusa': Dwarf variety that grows 3 to 5 feet high and 3 to 6 feet wide and rarely produces cones
- P. pungens 'Moerheimii': Grows to a medium height, with a maximum around 30 feet tall
- P. pungens 'Montgomery': A dwarf variety that grows 5 to 6 feet high and has dense, blue needles
Colorado blue spruce trees do not need to be pruned, but they can be if you wish to promote denser foliage. Prune off half of the fresh growth on each candle (that is, the tip at which branch growth occurs each year) in spring. Apply 2 or 3 inches of garden mulch around the plants (but not up against the trunks) to help retain moisture in the soil.
The two most common pests affecting Colorado blue spruce trees are aphids and the Cooley spruce gall adelgid. The former will cause yellowish blotches on the needles, which may have a sticky material on them, while the latter can be identified by the presence of a cotton-like substance of the spruce's branches. Manage the pests by hiring a company to spray a horticultural oil that won't endanger birds or humans.
The trees can also be affected by diseases, the most common and destructive of which is Cytospora canker. This fungal disease typically affects trees that are 15 to 20 years or older and causes the needles to turn brown and drop from the branches. Cytospora canker is a stress-induced disease, so manage it by reducing potential stressors, such as improving soil quality.
Blue Spruce: Common Health Issues in the Landscape. University of Massachusetts Amherst Extension Landscape, Nursery and Urban Forestry Program.