Question
We have 5000 3 - 4 year old Colorado blue spruce.
What kind of fertilizer should we be using and when should they be fertilized?  3500 of them have just been planted this year.
Thanks,
David Cookson

Answer
Best time to fertilize is in early spring before new growth.

Unless you are trying to grow the trees in unusual poor conditions (heavy clay or very sandy soil) fertilization should be kept to a minimum as these trees are not heavy feeders. A slight application every 2 years should be sufficient. Otherwise, keep an eye out for nutrient deficiencies (if the tree color or growth is not as expected).

Make sure you water your trees reguarily through the first couple of years. A deep soaking weekly in the growing season is recommended especially through the first two summers.

For fertilizer you can either apply single element fertilizers such as ammonium nitrate, superphosphate triple, and potassium sulfate, or use 10-10-10 if available in economical amounts. Use about 2 tbsp per small tree of 10-10-10