Question
Hello. I live in upstate New York and have some hemlocks which were planted several years ago. Is it OK to let them grow as tall as they will, or is there a benefit to topping them off(and if so, to what height)?

Thanks.
David

Answer
By all means let it grow. Topping tree can kill them or on the very least cause them to become bushes.

According to Dr. Alex Shigo, world renowned scientist and author on the subject of arboriculture (trees), topping is the most serious injury you can inflict upon your tree.  Severe topping and repeat topping can set up internal columns of rotten wood, the ill effect of which may show up years later in conjunction with a drought or other stress.

Topping creates a hazardous tree in four ways:

IT ROTS.  Topping opens the tree up to an invasion of rotting organisms.  A tree can defend itself from rot when side branches are removed, but it has a hard time walling off the pervasive rot to which a topping cut subjects it.  Rotted individual limbs-or the entire tree-may fail as a result, often years later.
IT STARVES.  Very simply, a tree's leaves manufacture its food.  Repeated removal of the tree's leaves-its food source-literally starves the tree.  This makes it susceptible to secondary diseases such as root rot---a common cause of failing trees.
WEAK LIMBS.  New limbs made from the sucker or shoot regrowth are weakly attached and break easily in wind or snow storms-even many years later when they are large and heavy.  A regrown limb never has the structural integrity of the original.
INCREASED WIND RESISTANCE.  The thick regrowth of suckers or sprouts resulting from topping make the tree top-heavy and more likely to catch the wind.  This increases the chance of blow-down in a storm.  Selectively-thinned trees allow the wind to pass through the branches. It's called "taking the sail out" of a tree.