By: Chad Burrer

Picea pungens, known as the Colorado blue spruce, is a coniferous, slow growing tree used in many landscapes. The Colorado blue spruce is native to the Rocky Mountains. The following are techniques to successfully propagate the beautiful spruce.

Stem Cuttings
Although success in rooting stem cuttings is not common, it has been known to be possible. Success increases with taking cutting from vigorous containerized trees. Shoot terminals gathered in early morning give the best results because the wood is more swollen. An IBA treatment between 0.3% and 1.0% is also beneficial. Using lateral stems for cuttings will produce an undesirable, prostrate plant, so upright stems are recommended. Research shows that a sand-peat mixture medium is best.

Grafting
If grafted, Picea pungens is usually grafted onto a dormant Picea abies rootstock during the winter months. Soaking the scion bases in 200 ppm IBA for three minutes before grafting is beneficial. Air layering has also been practiced successfully.

Micropropagation
Picea pungens can be vegetatively micropropagated by somatic embryogenesis. Somatic embryogenesis reestablishes the juvenile phase of a plant’s life cycle. With somatic embryogenesis, rejuvenation can be restored from mature parts of the plant.

Seed Propagation
Picea pungens is monoecious, meaning that both the male and female parts are on the same plant. Seed production for Colorado spruce begins at approximately 20 years of age. A normal tree will produce a full crop of cones only every two or three years. Seed begins to shed from the cone in September. Natural reproduction of Colorado spruce is not common, probably because the light seed does not make proper contact with the ground. However, seeds will germinate on a variety of media. Colorado spruce was once thought to have embryo dormancy, but research now claims that they do not. Seedlings will grow continuously if they are exposed to more than 16 hours of light per day. Seedlings will enter dormancy when they receive less than 12 hours of light per day. Dormancy can be prevented with a 12 hour light day period with a two hour light break during the night with red or white light. Seedling growth is very slow, ranging from 15 to 23 inches in height during the first five years.

References:

U.S. Forest Service: Picea pungens

University of Leeds: Picea pungens

Hartmann, Hudson T., and Dale E. Kester. Plant Propagation: Principles and Practices. 7th Ed. 2002. p. 667.

Janick, Jules. Horticultural Science. 4th Ed. p. 102.