Summer always brings many questions; it's time to answer some of them.
QI have a lawn that is inundated with violets. Please help me get rid of them. I have tried Weed-B-Gon, but that didn't work. -- Judy Slifer
AWild violets usually thrive in moist, shady conditions that aren't the most hospitable to turf. Lawn does best in full sun and moist but well-drained soil. The violets can be controlled with a non-selective herbicide containing glyphosate, such as Roundup. This will kill all actively growing vegetation, lawn included. That's okay if you are willing to consider another planting for the site, such as sedge, pulmonaria, tiarella or woodland phlox.
If grass remains your plant of choice, you can try spot-treating violets with a glyphosate. Remember, it is non-selective and will kill any greenery it contacts. Violets are tenacious and might need to be treated more than once. Ten days after the second spray, rake areas that are brown or bare with a leaf rake for good soil contact, and spread grass seed. Keep seed moist so it grows this fall. In spring, keep violet seeds from germinating by treating with a pre-emergent herbicide containing DCPA, such as Dacthal crabgrass control. It also inhibits grass seed. Turf should grow through a couple of mowings before you treat with pre-emergent materials in spring.
You advised not to "gnaw on the stick you use for roasting marshmallows" because it's toxic. Do you know whether these limbs are toxic when composted and spread in a garden? We occasionally throw limbs from our cherry tree into our compost bin. Should I be concerned? -- Lori Miller
You can compost those materials. The only no-nos for a compost pile are diseased plants, cooked food, meat scraps and plants in the nightshade family, such as tomatoes, peppers and potatoes, because they could cause a fungal buildup in your soil.
We are using thyme between the stones of a walkway by the pool area and the pumphouse. This is the second summer that dry black areas about 10 inches across have appeared. Scattered healthy growth exists within these areas. Can you help? -- Peggy Carlson
Thyme is not a long-lived perennial in this region unless the soil is light and airy. It is happiest growing in soil that is almost all gravel. If you have compaction, excess moisture and/or shade, thyme can decline quickly. It probably has a fungus. You can improve your soil by digging a generous amount of tiny "pea" gravel and compost into the top three to six inches. If possible, improve sunlight into the area.
Another option is try another plant. Mazus (M. reptans) has worked well for us in sun and some shade. It needs moist, well-drained soil, has showy lavender-blue or white flowers in May, grows about one to three inches tall and will mass vigorously around your stones. Corsican, or creeping mint (Mentha requienii), will have a mossy, mat-like appearance; it thrives in moist soil and emits a minty fragrance when bruised. Creeping Jenny (Lysimachia nummularia) is one the most dependable, low-growing, four-inch-tall, plants for places where soil is moist. It is sometimes too vigorous.
I use Preen to keep weeds from sprouting in the driveway. Since I use so little fertilizer on the grass, I would prefer not to have to buy another material for crabgrass control. I was surprised to read on the Preen label that it should not be used on lawns. Is there some legitimate reason to forego Preen on lawns? -- Jack Barnes
My compliments for doing what I implore all readers to do -- read the label before using. Preen is made in two formulations. One is what you are using on your driveway. It should not be used on lawn because it's a non-selective herbicide that will kill all vegetation it contacts. Preen 'n Green for Lawns can be used on your turf. It prevents annual grassy weeds and is effective against a large variety of summer broadleaf weeds. It also prevents annual fall grassy weeds, such as annual bluegrass, and winter broadleaf weeds, such as henbit and common chickweed. It's designed to keep weed seed from germinating and to cause actively growing weeds to absorb the herbicide and permanently kill roots and leaves. Unfortunately, this material is only sold as a blend with fertilizer. Try the more environmentally friendly corn gluten-based pre-emergent crabgrass controls. To make sure you are using the right material for the job, always follow labeled instructions.
I have had a magnolia tree in my yard for 23 years. It is the common large, shiny leaf type -- grand something, I think. This tree has never blossomed or flowered. Do you have any advice you might give me that would help this tree flower? -- Vincent Sodd
You are describing southern magnolia (M. grandiflora). It has large, shiny evergreen leaves and is a native plant that occurs from this region south. This is not usually a heavy flowering tree, but it's my favorite blossom for fragrance. Your tree was probably started from seed. Seedlings might take 30 years to bloom; others can flower within three or four years. Spread a general purpose 5-10-5 granular fertilizer over the root surface this month. Southern magnolia roots are very near the surface, so there is no need to dig it into the soil. The fertilizer needs only water to work. Also, the more sun trees get, the better chance they will flower. Enjoy this one for its foliage, and plant another that will offer fragrant blossoms. There is so much variation in seed-grown southern magnolias that you should see the flowers or seed pods on the tree before buying it at the garden center. Then you know it will bloom. A good, full-growing, cold-hardy variety is Bracken's Brown Beauty. A smaller-growing hybrid is Little Gem.
I have three blue spruces. For the first four years, all grew uniformly. All receive full sun and have good drainage. Each spring I use Holly-tone and cypress mulch. Last year, two of the three began to look unhealthy. Many of the lower branches lost their needles. This spring, though there is new growth on the outer branches, some branches have continued to lose their needles, especially the lower ones. Needle loss is most prevalent on the inside of the trees close to the trunk. The upper branches have no needle loss. There are some white splotches of what looks like paint on the lower trunk. The third tree has continued to grow vigorously. Can you offer assistance? -- Terry Consavage
Spruces tend to lose needles when they are in a low-light situation, such as being shaded by their own growth. Therefore the new foliage on the outer edge of the tree will be healthier than the inside needles.
Spider mites can be a problem on spruce and cause needles to get pale and drop when the growth is too tight and full and trees can't get good air circulation. Tap affected branches onto a piece of white paper, and you would see minute brownish-red specks crawling on the paper. If you see mites, they would need to be treated with a product labeled for mite control on blue spruce. Aphid damage in late winter could also be showing up in the form of dead needles now. When the damage is evident, it is too late to treat for aphids.
The white splotch on the wood of the tree could indicate die-back caused by a fungus. There is no treatment for this, but you can prune the dying wood and hope that cool and moist climate conditions will allow the tree to recover. Clean pruner with bleach and lightly oil when finished. For a definitive diagnosis and treatment, call a consulting arborist or a tree company with a research lab. You can find one under the "Tree Service" listings in the telephone book.
Joel M. Lerner is president of Environmental Design in Capitol View Park, Md. E-mail or contact him through his Web site, www.gardenlerner.com.