Information on the following concerns can be found at Why Do Pine Trees Turn Yellow? Prevent Yellowing With Expert Tips (treestopsecrets.com).  Please note that MPCD has no affiliation with Trees Top Secrets and does not specifically endorse them. They just have some good information about the subject matter.
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There are many reasons why conifer needles might be discoloring.

1. Natural Needle Drop in the Autumn
2. Pests and Disease
3. Nutrient Deficiencies
4. Sun Scald
5. Overwatering Issues
6. Improper Planting Consequences

For newly planted seedlings (like those received through our tree seedling program), the discoloring is most likely due to OVERWATERING or IMPROPER PLANTING.

For more information on tree planting and care, check out the following links:

• Tree Planting Instructions
• Colorado State Forest Service Tree Care videos