Question: The first year we moved into our house, the lilacs and forsythias bloomed wonderfully. Ever since that first year they haven't bloomed. The plants look very healthy all summer; they just don't bloom. What can we do?

Answer: It sounds like you are having a common problem that is a result of pruning at the wrong time. My guess is that you prune your shrubs in the fall or winter. Shrubs that bloom in early- to mid-spring, like lilacs and forsythias, set their flower buds during the late summer and fall of the year before. If you prune these shrubs in the fall or winter, you are removing the flower buds.

For spring-blooming shrubs, wait to prune them for size until they have finished blooming. Your other shrubs that bloom in summer or fall can still be pruned during the winter, since they produce flower buds on each year's new growth.

Q: The leaf tips on all my houseplants turn brown and die. I fertilize regularly and the plants grow well, but within a couple of months after emerging, each new leaf gets the dead tips. What is wrong?

A: Don't feel too bad. The problem has to do with the mineral salts found in most municipal water supplies and wells. Salts are not good for plants, so as soon as a plant absorbs salts through its roots, it tries to store the salts as far from its vital organs as possible. That place is in the tips of the leaves.

To correct the situation, periodically flush the roots and potting mix with filtered water. Even better, put your plants outside during a few of our warm, summertime thunderstorms. They will appreciate the opportunity to have their root zones flushed, and they'll show it.

Joel A. Reich is a Colorado State University horticulture agent in Boulder County.