Colorado blue spruces grow best in acidic soil.
With its slow growth and attractive color, Colorado blue spruce (Picea pungens) works well as an ornamental tree in many yards. Varieties of this conifer include dwarf trees that only reach 5 feet tall, trees with weeping branches and those with silvery needles. Whichever variety you choose, planting your Colorado blue spruce in the proper soil will help it thrive.
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The Colorado blue spruce is native to the western coniferous forests of North America. The soil in these regions is acidic due to the continual breakdown of conifer needles. Colorado blue spruce trees available to gardeners do best in soil with a pH between 4.5 and 6.0.
Colorado blue spruce trees won't tolerate soils that remain wet for long periods of time, such as clay soils. They also need soil rich in organic matter, so sandy soils won't suffice. The best soil for your blue spruce is a loose and fertile loam.
Adjusting Soil pH
To lower your soil pH to a range better suited for the Colorado blue spruce, you can either amend the soil prior to planting or mulch the soil around an already established tree. Peat moss, conifer needles or conifer bark chips will all make your soil more acidic. If you happen to have soil that's too acidic for your tree, raise the pH with a liming agent or wood ashes.
Improving Soil Type
If you have clay or sandy soil, you can amend it to make it more suitable for the Colorado blue spruce. For either soil type, prior to planting your tree work in at least 1 cubic foot of compost deeply into the planting area. When you plant the tree, fill in the hole with either compost or potting soil. Gardeners with clay soil will improve drainage by working in sand to the area as well. Use a four-to-one compost to sand mixture.