- Dehydration can cause purple needles on spruce trees. Sometimes spruce trees become dehydrated because construction or other human activities damage their roots. Other times, too much fertilizer or salts in the soil can dehydrate the trees and cause purple needles. A fungal disease called rhizosphaera needlecast also causes purple spruce needles (or can even result in needles falling off).
- Michigan State University recommends fine-textured loam and clay loam soils for spruce trees. These somewhat dense soil types contain more moisture and nutrients than sandy soils, which often have poor nutrient content. However, spruces also do not grow well in compacted clay soils with little aeration. Spruce trees with the wrong soil type can have damaged needles, which may appear purple before turning brown and falling off. According to Ohio State University Extension, spruce trees also become more susceptible to the rhizosphaera needlecast disease when they suffer from environmental stresses, like poor soils.
- To prevent purple needles on spruce trees due to poor soils and diseases triggered by the environmental stress of poor soils, plant trees in areas with fine-textured loamy soils. Also water spruces in extremely dry weather. Mulching around the base of spruces can also help keep them healthy. Maintaining the correct balance of soil nutrients can prevent diseases and purple needles. The University of Minnesota recommends getting a soil test to determine the amounts of nutrients in the soil around spruce trees. University laboratories and plant nurseries often perform soil nutrient tests and recommend fertilizers for a small fee. Most evergreens do best with high-nitrogen 16-6-6 fertilizer. Apply fertilizer if soil tests show low nutrient levels or a tree's growth slows dramatically. However, most adult spruces need very little fertilization. When unsure on fertilizer amounts, consult packaging instructions.
- Although prevention of tree damage is easier than fixing existing damage, you can try to remedy purple needles on spruces. Provide water for the trees during dry fall and winter weather, as Colorado State University Cooperative Extension suggests. Avoid de-icing salts or excess fertilizers if the tree turned purple after salts or fertilization. To get rid of rhizosphaera needlecast, Ohio State University Extension recommends a fungicide containing chlorothalonil when the tree has newly emerging needles. Agricultural chemicals, including fungicides, sometimes pose health or environmental risks; use them safely in accordance with their instructions.