We are having an erosion problem with two large boulder walls in our condo association. We want to preserve the looks of the boulders and not cover them up completely, but yet need to retain the soil around the rocks. We thought about vinca, pachysandra, vetch, etc.

There are several ground covers or filler plants that would work well to control the erosion and compliment the boulder wall. The plants chosen will depend on the amount of available light. First review the four categories of light and then choose your plant or plants. All recommendations reflect low maintenance plants that will not completely cover the boulders, help control the erosion and will take dry soil, because of the hill condition.

The four light conditions are dense shade that has no direct sunlight, and is mostly reflected light under trees or evergreens, or against a north wall. Moderate shade is filtered or reflected light with almost no direct sun. Part sun has filtered sun and a few hours of direct sun. A minimum of six hours of direct sun is considered full sun.

Some nice plants for direct to part sun that also have wonderful blooms include the herb thyme (several varieties with fun fragrances like lemon or coconut), hens and chicks (Sempervivum) grown for their succulent foliage, low-growing sedums with red blooms like ‘Bronze Carpet’ or ‘Dragons Blood,’ and candytuft (Iberis sempervirens) with white blooms.

For part sun to moderate shade try the hardy and fleshy ice plant (Delosperma nubigerum) with nice yellow blooms in May.

Plants that will grow in many light and adverse soil conditions include sweet woodruff, which thrives in dense shade to part sun and blooms in spring. Also, several varieties of Lamium that thrive in full sun to moderate shade bloom in spring and sometimes rebloom in fall. My favorite is ‘White Nancy’ which has white blooms in spring and silvery foliage that “glows” in the dark.

Many of the plants mentioned above can be purchased by the flat to make them more economical to plant in large areas.

Of the plants you have already considered there are some things to keep in mind. Vinca spreads easily and will quickly force out native woodland plants if your wall is not in a completely landscaped area. Similarly, vetch is an extremely vigorous invasive plant. Pachysandra, although not as invasive as the other two, is just not very suitable for growing on a wall.

Whichever plants you decide upon, keep them well watered until they get established, and plant with a slow-release fertilizer.

About 12 years ago I purchased a 1929 English Tudor, which at one time had beautiful rose and perennial gardens. Unfortunately they were left to die out except for invasive star of Bethlehem. This has surrounded the house. In the past three years I have dug up every bed and sifted all the soil. All I did was disrupt them; every little baby developed into healthy adult bulbs. What must I do to rid the beds of these menaces? They come up like weeds every spring.

There’s no sugarcoating this…You do have some work ahead of you. Here are several options, listed in order of effort.

1. Continue to dig them out every spring; this could take years to get rid of them.
2. While a little time consuming, using boiling water is very effective without using chemicals. (Be sure you wear a long-sleeved shirt, closed-toe shoes, and long pants to protect your skin should any of the water splash on you.) If the tubers are several inches under the soil, stir them up enough to get the tubers closer to the surface, and pour the water on them at very close range. Watch for new growth and repeat.
3. If you have not already replanted the area(s), cover them with cardboard (or a thick layer of newspaper) and a heavy layer of mulch for one entire growing season. The cardboard and newspaper can be turned under the following year as compost. Any plant must have light to survive and store food; depriving them of that results in death. But these guys don’t go down easy; some may survive and will require digging out or boiling water. Another option is to cover the area with thick black plastic.
4. Finally, spray with a vegetation killer and wait. Spray any survivors. This means everything dies, including many living organisms that are good for the soil. This type of product also leaches into the soil because the plants don’t usually consume all of it. Be doubly cautious about the quantity used and mindful of any nearby water sources.

Are all hydrangeas perennials? If not, how can you tell which are or which are not?

All hydrangeas are either woody or herbaceous perennials. The problem for northern states like Michigan is that not all hydrangeas are winter hardy, and are not able to take the Zone 5 winters that can dip to -20 degrees. We seem to crave those bigleaf hydrangeas (Hydrangea macrophylla) with lovely pink and blue, large lacecaps. They do not do well in Zone 5 unless extremely well-sited. Once you travel south into Zone 6 and beyond, the plants become more common and successful. In Zone 5, these hydrangeas should be considered container plants to be brought inside for the winter.

There is a climbing hydrangea (H. petiolaris), which is winter hardy here and can be used both as a shrub or a disguise for a large structure. It produces a white blossom in late June that is fragrant and lasts for two weeks or more. Two other hydrangeas with a large shrub or spreading tree habit are panicle hydrangea (H. paniculata) and oakleaf hydrangea (H. quercifolia). Both are winter hardy and work well in a larger landscape. In both cases, it is important to obtain a named variety from a reputable nursery to insure plant characteristics live up to your expectations.

We get dead circles in our grass. Inside the circle, the grass looks fine. We have had the grass replaced, aerated, and seeded, yet the problem keeps returning. How do we fix this?

The symptoms you describe are characteristic of yellow patch (caused by a Rhizoctonia fungus), sometimes known as “frog eye” or “summer patch.” It occurs during hot, dry and windy weather near the end of summer. Drought-stressed, shallow-rooted Kentucky bluegrass lawns are the most susceptible. It often shows up near paving or parts of the lawn that dry out first.

You need to review your lawn maintenance and cultural practices. Overuse of nitrogen fertilizers and excess thatch can make the problem worse. By aerating, you have taken a step to reduce thatch and improve water penetration. Make very sure that your mower blades are sharp, and that the grass is mowed no shorter than 2-1/2 inches. Mowing too short sets the lawn up for weeds and further disease. When you water, water deeply to wet the entire root zone and water consistently. Do not let the turf dry out. Betting on Mother Nature to be cooperative with her rain showers can often make the homeowner the loser in the “turf stakes.” Apply less nitrogen, particularly in midsummer, on Kentucky bluegrass lawns.

If you find you must reseed, select resistant varieties. Studies have also shown that simply adding a small percentage of perennial ryegrass to bluegrass can greatly reduce the problem.

We are able to get free ash tree chips from local landscapers. Most of the chips are less than 1 inch, but there are occasionally large wood chunks. Are these chips safe to use? Will we be bringing the emerald ash borer (EAB) into our yard? We do not have any ash trees, but can these insects cause harm to other plants?

Using the chips is not likely to introduce the ash borer, but it is possible. When Genesee County was outside of the EAB quarantine zone, some trees became infested near the processing plant that was burning the ash chips.

If you live outside of the quarantine zone (note that virtually all of southeastern Michigan is in the quarantine zone), do not bring in ash chips on the small chance of accidental infestation. If you live within the quarantine zone, feel free to use the chips.

So far there has been no known instances of the EAB infesting any plants other than ash trees.

When I lay down newspapers to smother weeds and build a new garden bed, is there any danger of the newspaper inks leaching into the soil and being toxic?

Today’s newspaper ink is largely based on soybean oil. It has been on the newspaper market since 1989. You might have noticed if your hands are moist when reading the paper that the ink more readily smudges. If you have any questions about the particular newspaper you are using, call them and ask what kind of ink they use.

It is preferable to use only the black and white newsprint for smothering weeds or grass to create a new garden bed. Some of the older colored inks contained petroleum-based solvents or oils with pigments containing toxic substances. Although, with society’s emphasis on recycling, most newspapers are now using vegetable dyes even for colored advertisements and the comics. Again, check with your newspaper of choice.

Any glossy pages, however, are covered with a clay coating that retards decomposition. So do NOT use or compost with any of the advertising inserts. These ad inserts are printed by someone other than the newspaper and can contain the heavy metal inks toxic to microorganisms.

If you are preparing a vegetable bed, you might feel safer cultivating the weeds and soil manually. However, the soy-ink newspaper smother is still one of the fastest ways to make a new bed ready for the eager home gardener.

I moved into a new subdivision where the yards were, of course, very hard clay (no top soil remained after the construction). I brought in top soil when I installed my sod lawn, which now looks great. A neighbor said that someone told him it was not necessary to put down top soil; that the sod can be placed right on top of the clay. Is that correct?

The overall health of your lawn is a direct result of proper soil preparation prior to the installation of the sod. The effort you put forth now determines the quality of your lawn for years to come. It also makes a difference in the routine maintenance that you will have in the future. It is very difficult to improve the soil at the root level once the lawn has been established. Sod that is laid over a thin layer of topsoil or compacted subsoil produces disappointing results due to poor rooting and development. It is a good idea to have a soil test done by your county MSU Extension to determine the pH and amendments that are needed. The following steps are recommended for sod installation:

1. The existing soil should be tilled thoroughly.
2. Add organic material if the soil is very heavy or sandy.
3. Topsoil that has been added should be well mixed with the subsoil to a depth of about 6 inches.
4. Apply recommended soil amendments and fertilizers at this time. In general, a pre-plant fertilizer can be spread over the entire area at a rate of 1 pound per 100 square feet.
5. Rake the area smooth, filling in the low spots and removing larger clumps.
6. A finish grade should be made using a steel garden rake, making sure that there is a way for water to run off away from the house.
7. After laying the sod, roll it with a water roller to remove air pockets.
8. Water, water, water. The sod should be kept constantly moist and should be watered 2 or 3 times a day for 10 days with heavy foot traffic avoided for the first two weeks. And then, let the mowing begin!

I have an invasion of wild violets in my lawn. What should I do to get rid of them?

I hate to be the bearer of bad news, but once violets have established a foothold in your lawn, they are extremely difficult to get rid of. Unfortunately, we have no good selective herbicide for violets. The trimec sprays may temporarily slow them down, but they usually bounce right back. Try using Roundup, a nonselective product. If the violets are just getting started, spraying small areas of the lawn and reseeding those areas after the kill is complete is an option. Another option is to paint the Roundup solution on the violets, avoiding the grass as much as possible. Since Roundup is absorbed through the leaves (not the roots), this is an effective approach that does little harm to the grass. On the other hand, if the violets have invaded a larger area of your lawn, you have to make a decision: 1) kill both the grass and violets and start over, 2) if you are very patient, paint every violet leaf in sight, or 3) learn to live with the violets (the flowers can be quite attractive!). The third option may work for naturalists, but lawn purists would be appalled!

Since it is difficult, if not impossible, to hold these violets captive, do not plant them in the first place unless their spread is your goal. If they do escape to your lawn, the earlier you attempt to bring them under control, the more successful you will be in getting rid of them.

What plants will grow well under pine trees?  The space is quite shady and has pine needles pretty much covering it. The soil is fairly dry.

Although it can be challenging, it’s a myth that nothing will grow under large pine or spruce trees. The reason many plants don’t thrive under evergreens is dense shade and extreme dryness. The trees have dense root systems and are strong competitors for soil nutrients and moisture.

The cure: If you plant perennials where they face dry shade conditions, give your shade garden plants the best possible chance by watering deeply and fertilizing more often than you normally would, and put a layer of mulch down. To let more light into your shade garden, consider elevating trees by cutting off some of the bottom branches. This works with deciduous trees, pine trees or thin older spruces, but don’t do this if your evergreen is a perfect Christmas tree shape with branches down to ground level. In that case, I would just mulch under the tree rather than disfigure it. The following is a list of some “survivor perennials” for dry shade you might want to try:

• Barren strawberry (Waldsteinia): A low-growing, dense mat of leaves that slightly resemble those of strawberries.

• Big-root geranium (Geranium macrorrhizum): Attractive and aromatic leaves, flowers in late spring in colors ranging from white to pink and magenta, depending on cultivar. Not to be confused with the common annual geraniums of the genus Pelargonium.

• Barrenwort (Epimedium x versicolor): Attractive heart-shaped leaves. With its delicate yellow flowers, ‘Sulphureum’ is the most popular cultivar.

• Dead nettle (Lamium maculatum): Look for cultivars such as ‘Beacon Silver’ with rosy pink flowers and silver leaves edged in green or the white-blooming ‘White Nancy.’

• Heart-leaved bergenia (Bergenia cordifolia): Large, leathery leaves and rose-pink flowers in early spring. Looks great in a big grouping.

• Sweet woodruff (Galium odoratum): Finely textured leaves and white flowers in spring. This is a top-flight groundcover in the dry shade garden. Note that it can be invasive.

• Groundcover plants: To make it really easy, consider the big three ground covers: ivy, pachysandra, and periwinkle, which are all tough evergreen perennial plants, perfect for the shade garden.

I have several plantings of the narrow arborvitae ‘Emerald.’ During this past winter and especially with the late spring snow fall, they have become bent over about midway up, even though we shook off the snow-laden branches. Is there anything I can do now to help them return to their straight, upright growth habit?

Due to their multi-stemmed nature, arborvitae and junipers are especially susceptible to having their limbs distorted from heavy snow loads. These loads cause the branches to bend and separate from the center of the plant. If the snow load is heavy enough, the branch can break.

Snow should be removed as soon as the storm stops by either using a broom to jostle the branches, gently shaking the tree so as not to damage the bark or by sweeping upwards. In case the weight of the snow has severely bent an individual branch, try re-positioning it by tying it to other branches within the shrub.

In more severe cases, like with yours, you can attempt to straighten them by tying a soft rope (their bark is thin), even old panty hose or stockings will do, around the trunk. You will need to tie above and below where it’s bent. Attach a rope to that and pull the tree straight. You will have to anchor the rope and leave it on for at least 6 months if they have been bent for a while. There is no guarantee that they will straighten, but it’s worth a try.

Evergreens can be protected from snow breakage by tying the branches together with strong rope or twine before winter snows are expected, but after the first severe frost. Fasten it near the tip of the tallest branch and then spiral down around the entire tree and tie it off to the base. You do have to remove it at the first sign of spring.