Colorado blue spruce

About Colorado blue spruce

Colorado blue spruce is a stiff, pyramid-shaped evergreen from the Rocky Mountains, grown for its silvery-blue, sharp-tipped needles. It does best in cool climates and cannot take hot, humid summers. In much of the Midwest and East it often loses lower branches to Rhizosphaera needle cast, so UMN suggests better-adapted spruces there.

Zones 2-7 (NC State); in the Southeast it manages only in the mountains.

When to plant

Timing is counted from your average last spring frost (and first fall frost). Sow & Tell works out the actual dates for your ZIP code.

Plant container or balled-and-burlapped trees. Container trees can go in any time the ground can be worked, but fall is the best season in the South because roots keep growing through mild weather (Clemson). Dig the hole no deeper than the root ball and at least twice as wide, keep the top roots level with the soil, and mulch 2-4 inches without touching the trunk. Space trees by their mature size so air moves through, don't shear them, and keep sprinklers off the needles to limit needle cast (UMN).

Soil

Rich, moist, well-drained soil; acidic soil helps (UMN). Young trees must not dry out, but mature trees handle drought better than other spruces (NC State).

Test the soil first. Loosen a wide planting area and mix 10-20 percent compost into the native soil you dig out; don't use uncomposted bark, and don't dig deeper than the root ball (Clemson).

Feeding

• Spring to early summer, after the tree is established, and only if a soil test or pale leaves and weak twig growth show a need: slow-release nitrogen fertilizer with a ratio near 3-1-1 or 3-1-2 (3-0-1 or 3-0-2 if the soil test shows enough phosphorus). Spread it evenly from just outside the trunk flare to the dripline and water it in. Clemson cites 2-4 lb of slow-release nitrogen per 1,000 sq ft per year, split into a spring and a late-summer feeding; follow your soil test.
• Late summer to early fall, the second half of the year's split feeding (only if a soil test calls for it): slow-release nitrogen fertilizer, same as spring. Apply the rest of the year's amount over the root zone and water in. Don't feed a drought-stressed tree in summer (Clemson).

First-year watering matters far more than fertilizer: water daily for the first 1-2 weeks, every 2-3 days until week 12, then weekly, using about 1-1.5 gallons per inch of trunk diameter, until the tree is established, roughly 1.5 years per inch of trunk (UMN). Don't count on rain unless it was over an inch. Young trees must never dry out (NC State). Mulch 3-4 inches of wood chips with a 2-inch gap at the trunk, keep sprinklers off the needles, and don't shear (UMN). Too much fertilizer can burn roots and push soft growth that pests and cold injure (Clemson).

Varieties (3)

NC State describes 3 cultivars; it lists many more by name only (e.g. 'Baby Blue Eyes', 'Montgomery', 'Bakeri').

Pests to watch for

Spruce spider mite, Bagworm, Aphids, Scale insects

Diseases and problems

Needle cast, Overwatering and waterlogged soil, Leaf scorch, Normal needle drop, Diplodia tip blight, Cytospora canker of spruce

In the kitchen

Safety: The stiff, sharp needle tips can hurt small children; NC State notes this is why it is losing favor as a Christmas tree.

Pets: We found no ASPCA listing for blue spruce.