Both Canadian and Carolina Hemlocks respond to shearing and pruning. They can be maintained at 3 or 4 feet to make an attractive hedge. Clipped closely, the hedge will look more formal. If individual shoots are removed every year, rather than shearing the entire plant, a more attractive pleasing effect is achieved. If permitted to grow a year or so between prunings, it will acquire a soft, informal appearance. Prune in early spring using sharp, clean hand pruners or loppers.
Always prune out broken or diseased branches promptly to forestall disease and insect invasions. Cut branches off cleanly back to the point where the branch joins another and the wood is healthy. If you cut way back to older, bare wood, no new shoots will develop.
To keep the soil moist as well as to control weeds, spread a 2 to 4 inch layer of some attractive organic material over the soil underneath the Hemlock tree. Spread the mulch in a circle out as far as the drip line. Avoid piling it up against the base of the trunk.
Hemlocks like moisture, but are very intolerant of flooding. Their fibrous roots are shallow and dry out easily if rainfall is skimpy. Water newly planted young trees regularly until they are well established. Mature trees need supplemental watering just before the winter freeze sets in and in times of drought. Hemlocks are more sensitive to drought than most other narrow leaf evergreens especially when sited in southern exposures.
Fertilizing - Feed young Hemlocks once a year in the fall. After they have been planted a year, sprinkle an all-purpose slow acting granular fertilizer on the soil under the tree out to 1 or 1½ feet beyond the tips of the branches (the drip line). Do not allow the fertilizer to touch the tree trunk. Use 1 cup or so of fertilizer for every inch of trunk diameter. Do not fertilize newly planted trees, or those in place less than a year.
If your Hemlock is infested with wooly adelgid pest insects choose a fertilizer that is relatively low in nitrogen. This nutrient, so abundant in lawn fertilizer, seems to promote greater adelgid damage. If you maintain a layer of organic mulch on the soil under your Hemlock year round it will contribute balanced nutrients to the soil as it gradually decomposes. After a few years you no longer need to fertilize the tree regularly.