George Roche of the Maryland Department of Agriculture offers these tips in buying Christmas trees:
Take your finger and wrap a tree needle around it. If it bends freely without breaking, the tree is fairly fresh.
Gently bang the stub of a tree on the ground to see how many needles shake loose. The tree is not fresh if a lot of needles, especially green ones, fall.
Decide if you want a tree for its shape, color, needle retention or aroma. White pines have a strong aroma for example, scotch pines have good needle retention, spruces often have the best shapes and are more open for decorating. Color can vary within species of trees and some naturally have a yellowish color, but that doesn't mean they are unhealthy.
Cut 1/2 to one inch from the bottom of the tree in a stand that can hold several quarts of water, preferably almost a gallon of water. Believe it or not, a tree can take in several quarts of water the first couple of days.
Figure out where the tree should go in the house, stand there, reflect on your height in respect to ceiling height and space. properly locating a tree is one of the biggest problems people have.
When you find a tree, stand next to it, remembering the visual measurements taken inside the house. Trees always look smaller outside. If it fits your measurements, you may be able to get away with a smaller tree - at a lower price.