Question
I live in North Carolina ( gaston county) and I would like to know the best time of year to prune Leland Cypress tree's. I have some that are almost 30 feet tall and some that are around 7 to 8 feet tall. I would like to cut the top's out of the 30 feet and want to know if this is possible to keep them from growing any taller? Any pruning advice you can give me on the Leland Cypress would really help me alot since I have about 40 tree's planted in my yard for privacy.

Answer
Pruning: Little and often is the key, that way it doesn't get carried away and give you a massive job to do that you might put off, when it gets bigger, when you might put it off... you get the idea.
Doesn't respond very well to drastic renovation, though it is possible to remove large amounts of growth without harming the tree. The key is to not cut back into brown wood with no green foliage on show. If you do this it will almost certainly never recover. I have cut these down to about half the height and removed a substantial amount of the width without damage. However I have also seen plenty of examples of where people have tried to do too much and either ended up with one side green and the other side permanently brown or have lost the plant completely.

If you have a huge one to deal with, maybe it might be a good idea to think about total removal, cutting down to shape will almost always result in a permanently odd-shaped tree. This drastic pruning is best only tried with hedges which are block-shaped to start with

Leyland like many other conifers have green leaves on the outside only, once you cut back any distance into it, you just have brown branches. If the tree is quite large it is unlikely to grow green shoots again from the brown wood. Conifers that have been grown as trees usually respond to drastic cutting back by giving up the ghost completely.