Colorado blue spruce (Picea pungens) is a coniferous evergreen tree with sharp and short needles that belongs to the pine family. The official state tree of Colorado, this slow-growing spruce is native to the Rocky Mountains, where it was first discovered in 1862. In the wild the Colorado blue spruce can grow up to 75 feet tall. In parks and gardens it usually tops out from 30 to 60 feet high. Colorado blue spruce is one of the most widely used trees both for holiday decorations and landscaped backyards. Its pyramid shape, silvery-blue foliage color, and wonderful smell make it a classic choice for a Christmas tree. Then, when the holidays are over, seasoned gardeners like to use the tree's boughs to make a shrub shelter to overwinter garden bushes.
The best time to plant a Colorado blue spruce tree depends on your climate. You can plant spruce year-round in mild climates, but if you live in an area with harsh winters and frosts, it's best to plant this tree during the late winter or early spring (late February through April), when it's dormant. If you plant blue spruce in the early fall, there's a chance it will become susceptible to winter injury and die-back.
|Common Name||Blue Spruce, Green Spruce, White Spruce, Colorado Spruce, Colorado Blue Spruce|
|Botanical Name||Picea pungens|
|Mature Size||75 ft. high, 15-20 ft. wide.|
|Soil Type||Loamy, clay, sandy, moist, rich, well-drained|
|Soil pH||Acidic, neutral|
|Hardiness Zones||2-7 (USDA)|
|Native Area||North America|
Colorado Blue Spruce Care
An established Colorado blue spruce tree is easily maintained, as it only needs regular watering when it is first planted. Providing 2 inches of garden mulch around the base of the tree helps it retain moisture in between waterings or during drought years. Spruce trees benefit from a high-nitrogen fertilizer once a year in the form of compost, and they thrive in areas with several hours of filtered sunlight a day.
Plant Colorado blue spruce trees in full sun, ensuring they get at least six hours of unfiltered sun per day to reach their full growth potential. Blue spruce can tolerate some shade, but planting in a low-light area can increase disease incidence and severity.
A spruce tree grows best in a location with moist, well-drained soil made fertile through the use of soil amendments. However, this tree can adapt to a variety of soils—loamy, sandy, or clay. As for soil pH, spruce thrive in a range between 6.0 and 7.5, but its unfussy nature makes this tree able to tolerate extremely acidic or alkaline soils.
Once established, this tree is drought-tolerant and can survive periods of low water, but it thrives with scheduled waterings. During the first season, water the tree regularly to keep the soil moist. Once the tree is established, water it only during dry spells. Avoid waterlogging the tree or creating areas with standing water at its base.
Temperature and Humidity
A native to high mountain areas, Colorado blue spruce is tolerant of dry, cold weather. Still, this tree variety can tolerate heat and humidity better than other spruces. Blue spruce will not thrive in extremely hot conditions, however, as its needles will turn brown and fall.
These trees do not need frequent fertilization. That said, spring fertilization will give the tree an added nutrition boost and likely increase the length of the needles and improve needle color. Sprinkle 10-10-10 slow-release granulated fertilizer over the soil in the root zone. Then, water with about 2 inches of water to prevent fertilizer burn. Better yet, use a natural and pet-friendly option like compost, fish emulsion, cottonseed meal, or alfalfa meal, to avoid burn altogether. For fertilizer amounts, follow the product label instructions.
Types of Colorado Blue Spruce Trees
Colorado blue spruce comes in several varieties, all with beautiful silvery-blue needles:
- Picea pungens "Baby Blue Eyes" is a semi-dwarf cultivar that grows 15 to 20 feet tall.
- Picea pungens"Bakeri" features a deep blue color and grows 12 to 20 feet high.
- The dwarf variety Picea pungens "Glauca Globusa" grows 3 to 5 feet high, 3 to 6 feet wide, and rarely produces cones.
- Picea pungens "Moerheimii" has branches that droop and grows to a maximum of 30 feet tall.
- Picea pungens "Montgomery" is another dwarf variety that grows 5 to 6 feet high and has dense, blue needles.
Colorado blue spruce has a slow to medium growth rate, growing less than 12 to 24 inches annually. This tree does not need to be pruned, but can be if you want denser foliage. In this instance, prune off half of the fresh growth on each candle (the tip where branch growth occurs each year) in the spring.
Propagating Colorado Blue Spruce
Colorado blue spruce grows well from cuttings taken mid-summer and then planted in the fall. Cuttings take a while to root (two to three months) and need to be treated with a strong rooting hormone. Grow cuttings in cool and humid conditions for successful propagation. Here's how:
Gather your garden shears, an alcohol wipe, a paintbrush, a potting container, peat, medium-grit sand, 0.6-percent indolebutyric acid rooting talc, and a spray bottle.
Combine equal parts peat and sand in a bucket. Cover the mix with water and let it sit until the peat swells. After that, fill your potting container with the mixture.
Clean the blades of your shears with alcohol and cut a tip 4 to 5 inches long from one of the tree's side branches. Make an angled cut between two sets of needles.
Strip the needles from the bottom half of the cutting and peel the bark from the end. Brush the end with rooting hormone.
Poke a hole in the potting container equal to half the length of your cutting. Insert the cutting into the hole and backfill it with the peat mixture.
Place the pot in a cool indoor spot with filtered light. Avoid direct sun.
Drizzle water regularly onto the peat's surface, and mist the air above the cutting, allowing the water to fall onto the needles.
Check for roots after two months (it could actually take up to four months to root), and then move the pot outside into direct sun to acclimatize for a week, bringing it in each night.
Transplant the cutting into the ground in early autumn by digging a small hole, placing the baby tree and the contents of the pot into the hole, backfilling it, and then spreading a thick layer of mulch around the base. Water the tree regularly for three years until it's established.
How to Grow Colorado Blue Spruce from Seed
With patience, Colorado blue spruce can be grown from seed after collecting and drying pinecones to obtain the seeds. Come spring, soak the seeds in water for 24 hours and then wrap them in a moist paper towel and store them in the refrigerator for six weeks. Next, place a seed in a container filled with moist seed starting mixture, cover it with 1/4 inch of the mixture, place plastic wrap over the container, and relocate it to a sunny spot. Keep the mixture moist until the seed germinates and grows about an inch, then remove the plastic wrap. In all stages of growth, Colorado blue spruce is slow so this may take a while. Harden off the seedling by bringing it outside into direct sunlight for several days. Transplant the seedling to the ground once it's acclimatized, mulch around the baby tree, and water regularly for three years.
Colorado blue spruce is native to cold climates, therefore established trees do not need special care in the winter, as the tree will go dormant during this season. You can, however, spread a layer of mulch around the tree's base in the fall and wrap its trunk in burlap to protect it from hungry animals. Also, make sure to shake the branches after a heavy or wet snowfall to prevent them from snapping due to the snow's weight.
Common Pests & Diseases
The two most common pests affecting Colorado blue spruce trees are aphids and the Cooley spruce gall adelgid. The former will cause the needles to grow yellow blotches and become sticky, while the latter can be identified by the presence of a cotton-like substance on the spruce's branches. To ward off pests, hire a company to spray the tree with a non-toxic horticultural oil that won't endanger birds, pets, or humans.
This variety of tree can also be affected by disease, the most common and destructive of which is Cytospora canker. This fungal disease typically moves into trees that are 15 to 20 years or old, causing the needles to turn brown and drop from the branches. Cytospora canker is a stress-induced disease, so manage it by amending the soil regularly and not overwatering.
Common Problems with Colorado Blue Spruce
While blue spruce trees need ample watering during the first several years, it's easy to overwater them with this mindset. Signs of overwatering include browning needles, wilting branches, and die-off. To prevent this from happening, make sure the tree never sits in standing water, and provide ample mulch to keep moisture around the tree's base, allowing you to go longer in between waterings.
How is Colorado blue spruce used in landscaping?
Do blue spruce trees ward off animals?
What issues do blue spruce face in the wild?
Wild blue spruce trees are regularly affected by the great spruce bark beetle. This beetle has been known to take out full stands of trees by tunneling into the trees' bark and laying eggs. The holes weaken the tree, eventually causing die-off.
Blue Spruce: Common Health Issues in the Landscape. University of Massachusetts Amherst Extension Landscape, Nursery and Urban Forestry Program.