In addition to seasonal variation in tissue nutrient concentrations, variations also exist with respect to age as well as location of the tissue being sampled. We recommend you collect 2 to 3 ounces of needles from the current growing season growth, taken from the upper third of the crown of the tree, staying away from the leader.

If you are seeing a problem in your field such as off-color or poor growth, make sure to collect separate “good” and “bad” samples to potentially help diagnose a nutrient deficiency problem. Keep the samples cold and dry and mail them to the testing laboratory, such as A & L Laboratories, as soon as possible after they have been collected. Assign a sample name or number so you can keep track of the fields and take detailed notes if you are seeing problems.
Source:msue.anr.msu.edu