The Eastern Hemlock and Canadian Hemlock both like cooler environments to grow in. They generally fail in warmer urbanized areas. They also tend to begin to decline in areas where the soil has been disturbed heavily. Hemlock trees are vulnerable to Wooly adelgids, scale and spider mites. Older trees that are in decline (die back) are vulnerable to bark beetle infestations and borers. Generally the beetles and borers are the final blow to an infested hemlock, causing them to die completely. If you look at the trunk of the suspect tree, you may see tiny holes and saw dust on the bark or upper sides of the branches. The borers and beetles dig into the conductive tissues and creat feeding galleries under the bark, these galleries cut off the pipe line from the roots to the shoots. BUT, generally speaking these insects like to attack unhealthy trees first.
Trees that were originally growing in wooded areas that in recent years have been developed are stressed from the disruption in their growing environment. This stress makes them unhealthy. These trees take a few years to show stress signs making it almost impossible to save them as it may be too late to take action. Should you fertilize them?
Fertilizing Hemlocks with nitrogen based fertilizers is not reccommened because the new growth the fertilizer makes is food for the bad insects to feed on. We use a organic sea kelp based fertilizer with high iron content. We also will spray the trees with horticultural oil in the fall and the spring to control adelgids, scale and mites. They key to a happy Hemlock is to minimize soil disruption within the root system, irrigate them when possible in droughts, just enough to maintain plant hydration. Most importantly, get rid of trees that will be hosts of the beetles and borers.
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