I want to plant a perennial garden in the dappled shade below a large, old maple tree. Digging around the tree is really difficult due to all the roots; is it O.K. to create sort of a “raised bed” by adding 12-18” of topsoil beneath the tree and gradually sloping it down from the trunk to ground level?

This is a very common problem facing gardeners who are fortunate enough to have these established gems in their yards. Unfortunately, there are no easy answers that can be used in all cases. As a general rule, simply adding large amounts of soil around trees can cause severe damage when done improperly. The degree of caution depends upon the tree species, age and vigor as well as the depth of the soil and location it is to be placed beneath the tree.

The most sensitive area is near the trunk of the tree (which is where most of us want to plant!). Soil piled against the bark can cause it to decay, while covering the roots may prevent proper air and water exchange.

An inch or two of good soil spread over an area is usually safe. If you wish to add more than that, save yourself future grief by first hiring a licensed arborist to evaluate your specific situation. They will be able to best assess how much soil you might be capable of adding without injuring your valuable tree. You will have to pay for the service, but it will be far less than the cost of removing a dead tree, not to mention the loss of a beautiful, well-established specimen.

I bought a green and white ground cover. The tag said it was Aegopodium podagraria ‘Variegatum’ or “Snow on the Mountain.” My horticulture book says A. podagraria is called Bishop’s Weed or Gout Weed and that Snow on the Mountain is called Euphorbia marginata. I’m confused – please clarify.

Common plant names are a constant source of confusion in the gardening industry. The plant Aegopodium podagraria ‘Variegatum’ has only one distinct botanical name. The confusion comes from the fact that it may have several common names such as those you listed. To make matters worse, the same common name may be given to several different plants throughout various parts of the country. With today’s demand for increased variety selection, you’re finding many more plants available with overlapping common names.

George Papadelis, from Telly’s Greenhouse in Troy, adds: the common name “Snow on the Mountain” refers to both Aegopodium podagraria ‘Variegatum’ and Euphorbia marginata. The Aegopodium is a perennial while the Euphorbia is an annual. Be careful with the Aegopodium, as it is very invasive and can be extremely difficult to get rid of. The annual Euphorbia may reseed itself from year to year, but invasiveness shouldn’t be a problem.

Why don’t my lilacs bloom? They were planted 4-5 years ago and they get plenty of sun. The shrubs are 4-6’ tall, the foliage is healthy, but there are no flowers. Please help.

Stubborn lilacs may refuse to bloom for a couple reasons. First off, a healthy, fast-growing lilac may have received too much fertilizer which is causing the plant to develop vegetatively rather than reproductively. In this case, reducing the amount of fertilization will help slow the growth. Sometimes inducing a small amount of stress may cause the plant to set flower buds. This can be accomplished with careful pruning or by withholding moisture during dry periods. Never let a plant go completely dry to the crispy stage, but a slight hint of wilt during the summer may just be the right incentive for enjoying blooms next spring.

The second reason for lilacs not blooming may be due to improper pruning. Flower buds begin developing during the summer as soon as the new growth begins to harden. Any pruning done from that time forward may remove the terminal buds containing the flowers. Remember, the best time to trim a lilac is just after flowering – that is, once yours begins to flower!