The Troemner Spruce (Picea x ‘Troemner’) is a hybrid of Picea pungens and Picea omorika. It was selected by Allan Troemner from the University of Wisconsin Forestry Department in 1972.
Understanding the Troemner Spruce
The Troemner Spruce is an evergreen conifer, a hybrid of the Colorado blue spruce (Picea pungens) and the Serbian spruce (Picea omorika). It typically reaches a mature height of 25 to 50 feet and a width of 10 to 15 feet, exhibiting a broad upright or narrowly conical growth habit, sometimes with a sweeping or down-swept branch structure.
The needles of the Troemner Spruce are prickly, similar to those of the Colorado blue spruce, but possess a unique blue-green coloration, sometimes described as silvery-blue. This coloration is a blend of the blue hues from P. pungens and the green from P. omorika. It is a fast-growing tree, with an annual growth rate often exceeding 12 inches, and can reach over 2 feet per year. The tree is hardy in USDA Zones 3 or 4 to 8, making it suitable for a range of climates.
Planting and Establishing Your Troemner Spruce
Proper site selection is important for successful establishment. This tree thrives in full sun, requiring at least six hours of direct sunlight daily. It prefers well-drained, fertile, loamy soil that is rich in organic matter, though it can adapt to various soil types, including clay or sandy soils. Good air circulation around the planting site helps prevent disease.
When planting, dig a hole twice as wide as the root ball and approximately the same depth. If the soil is compacted, chopping the sides of the hole can help loosen it. Remove the tree from its container, loosen any circling roots, and place the tree in the hole so that the top of the root ball is level with the surrounding soil. Backfill the hole with existing soil, tamping it down to remove air pockets, then water deeply to settle the soil around the roots. Applying a two to four-inch layer of organic mulch around the base, keeping it a few inches away from the trunk, helps conserve moisture and suppress weeds.
Caring for Your Troemner Spruce
Consistent watering is important for established Troemner Spruce, especially during dry periods. While young trees need frequent, deep watering to establish their root system, mature trees become more drought-tolerant. Deep, infrequent watering encourages deeper root growth compared to shallow, frequent applications. Water thoroughly when the top few inches of soil feel dry.
Fertilization is not required for established spruce trees growing in healthy soil, but a soil test can determine if nutrient deficiencies exist. If needed, a balanced, slow-release evergreen fertilizer can be applied in early spring. Pruning is minimal; focus on removing dead, damaged, or diseased branches to maintain the tree’s health and shape. Winter care involves ensuring the tree receives adequate water in the fall, particularly if rainfall is scarce, to prevent winter burn, and applying mulch can help regulate soil temperature.
Common Challenges and Solutions
Troemner Spruce, like other spruces, can encounter certain challenges, though it shows some resistance to Rhizosphaera needle cast disease. One common issue is Rhizosphaera needle cast, a fungal disease causing needles to turn yellow, purple, then brown, starting on lower branches. Affected needles eventually drop prematurely. Improving air circulation through selective pruning and applying fungicides in spring before new growth emerges can help manage this disease.
Another concern is Cytospora canker, which causes branch dieback and resin oozing, often on lower branches, and is more common on stressed trees or those over 15 years old. Proper watering during dry periods, adequate spacing, and pruning infected branches during dry weather with sterilized tools can mitigate this issue. Pests like spruce spider mites can also affect spruces, particularly in spring and fall. These mites cause needles to become discolored; tapping branches over white paper can reveal their presence. Horticultural oils or miticides can be used for heavy infestations.