Q Every summer I struggle to keep up with deadheading the flowers in my garden. Are there any guidelines for which flowers need to be deadheaded and which I can just leave alone?

A Deadheading (removing faded, spent flowers) does several things. Most obviously, it keeps plants looking their best. Some flowers, especially those with many petals, will mildew or grow moldy when left to deteriorate on the plant. Others just look messy.

More important, removing a faded flower (along with the ovary at its base) ensures that no energy will be wasted on seed development. It also encourages the plant to produce more flowers. It's as if the plant's purpose is to create seeds, thus perpetuating itself. When that doesn't happen, the plant seems to redouble its efforts to produce flowers, which turn into more seeds.

Removing seed pods from peonies, daylilies and other perennials also helps save energy for the following year's growth, though it may not promote additional flower production.

Which flowers you deadhead depends largely on the amount of time and effort you can devote to the job. While it makes sense to nip off large flowers such as lilies, zinnias and clusters of faded geraniums, few people take time to deadhead any but the largest-flowering petunias or pansies.

So deadhead what you can. When you do, don't just nip off the petals. You must also take the ovary (the bulge, which sometimes sits below the petals, that contains the immature seeds) to get the real benefits of deadheading.

No luck with clover

Q How do I get rid of white clover in my lawn?

A White clover is a common problem in thin, poorly maintained lawns.

Garden centers do sell herbicides designed specifically to kill clover and chickweed, but it's not a good idea to use them in the heat of summer because the drifting spray -- and even the fumes -- can damage other plants. Instead, wait until autumn, when temperatures moderate, then use the product according to label recommendations, such as applying the spray when no rain is expected for at least 24 hours.

Getting rid of the clover is only part of the solution. You need to improve your lawn or the weeds will just come back.

Start by regularly watering your lawn this summer, having it aerated in late summer and fertilizing twice this fall. As the grass improves, you'll find less clover.

Roots of the problem

Q How can I get rid of chokecherry roots? They're ruining my garden.

A Woody plant roots can be a real problem in flower and vegetable gardens, whether they're from chokecherries, lilacs, maples, green ash, or just about any tree or shrub in the vicinity. Even if you manage to remove them, it's likely that those roots will grow back quickly. That's because when you fertilize and water the garden, you're also making the area more hospitable to tree and shrub roots.

If you want to keep the chokecherries, there's little you can do to discourage their roots, aside from cutting and digging them out every year. However, if you're not that fond of the chokecherries, you can cut them down and dig out as many of the major roots as possible. If any remaining roots sprout, continue to dig them out or spot-treat them with a nonselective herbicide such as Roundup.

Deb Brown is a garden writer and former extension horticulturist with the University of Minnesota. To ask her a gardening question, call 612-673-7793 and leave a message. She will answer questions in this column only.