During last season, my hosta leaves were really chewed up. Is this due to mites or slugs? Any recommendations on preventing it?

Mites are not what chewed your hosta leaves. It’s those slimy critters that are part of the mollusk family: slugs. They, as well as garden snails, use tooth-like jaws to saw through leaves and flowers. Like bats, these garden pests feed at night and on overcast or rainy days. They are most active during warm, rainy springs. While there are more than 25 slug species in the United States, hostas’ real enemies are the little black and brown slugs that eat both shoots and roots.

Slugs slide along on a slime trail that’s excreted by their single large foot. Their eyes are located at the end of the large tentacles on their head, while the smaller tentacles enable them to smell. Slugs are hermaphroditic, containing both female and male organs. Nonetheless, they need to pair in order to breed, usually in the spring or fall when weather is mild and moist. In fact, slugs are more prolific than rabbits, laying clusters of 40 to 100 gelatinous eggs in the soil, under rocks, and in outdoor pots. After hatching, slugs can mature in a few months; as adults, they can mate up to six times a year.

• While ridding your garden of slugs is not easy, there are many simple things you can do in the garden to decrease their damage:
• Eliminate their habitat. Garden debris provides a hiding place. Using less mulch will reduce your slug population.
• Hand pick slugs during the evening and early morning hours. Crush them or dispose of them in a bucket of soapy water.
• Add plants such as ginger, garlic, mint, chives, red lettuce, red cabbage, sage, sunflower, fennel, foxglove, astilbe, ferns, mint, chicory, and endive that have foliage and toxins less desirable to slugs. Also consider planting some of the blue type or waffled-leaved hostas that slugs seem to scorn.
• Create a barrier of abrasive material such as crushed eggshells, sand, wood shavings, diatomaceous earth, hair or ash around your hostas. Keep these materials dry and replenish them after it rains. Take care using diatomaceous earth as it may damage your lungs if breathed; use a face mask when applying it.
• Drowning slugs in beer is not as effective as you may think. Dissolving yeast in water can be just as effective and much less expensive. If you choose this option, bury several containers at ground level, empty them and refill them daily. However, you may have too many slugs for this method to be effective.
• Much of the slug’s body is water so they are susceptible to drying out. Cultivate your soil in early spring to expose their eggs to drying air & predators. Try to keep your garden as dry as possible without damaging your plants.
• Iron phosphate baits decrease slug populations without harming birds, small pets or humans. These baits are sold under the name Sluggo, Es-car-go, and Safer’s Slug & Snail Bait.
• Set up a barrier with copper strips or tape. Slugs will not cross the copper. When they slide over it, there is a toxic reaction, similar to an electric shock.
• Attract predators that eat slugs such as ground beetles, frogs, birds, and ducks.
• Lastly, try coffee grounds. Researchers have found that slugs have a real distaste for caffeine. The grounds themselves repel slugs, but a 1 to 2 percent caffeine solution kills nearly all slugs within two days.

I would like to know how to propagate the black gum tree. Is it true that it has a big tap root, so that is why you do not see it a lot in cultivation? What about stem cuttings? Is it hard to root? Would it take a very long time to get a medium-size tree from a stem cutting? Does this species need to be grafted?

The black gum tree (Nyssa sylvatica) is one of our most beautiful trees native to the eastern U.S. Somewhat pyramidal in youth with densely set branches, it grows about a foot a year, reaching about 15 feet in 15 years. It is an excellent specimen tree, acceptable for residential streets, but not in dense urban areas where pollution is high. Despite its outstanding, dark lustrous green summer foliage and its broad range of fall color from yellow to scarlet, it is often passed over.

You are correct that it has a big taproot. However, that probably isn’t the deterrent to more frequent urban cultivation. Balled-and-burlapped nursery stock for early spring planting can be readily obtained. More likely its need for swamp-like conditions, a soil high in organic matter with a pH of about 6.5, and a naturalized setting are what keep it from the current suburban developments. And although its stiff horizontal limbs and irregular bark may endear it to some, its overall irregular shape does not adhere to the script for a manicured yard.

Michael Dirr, author of Manual of Woody Landscape Plants, has raised numerous seedlings from seed. Black gums are generally not rooted from cuttings or grafts. Each half-inch oblong blue-black drupe contains a single seed. The fruit ripens in late September through early October. Since seeds are obtained in the fall, you will need to overwinter them. Dirr recommends using container culture and transplant the second spring while still a very small sapling. The potting mix should be moist, sterilized potting soil, enriched with organic matter. You need to mimic the conditions of a mucky swamp, which means watering the pot very well once the seeds are planted. Place the mucky pot in a large freezer bag and store in a location where the temperature will be near freezing over winter. Germination occurs in spring. Put the potted seedlings outside during the first growing season. Dappled sun is best to prevent scorching of the new leaves. Keep the pots well watered and fertilized. Overwinter in the pots, continuing to maintain the muck-like conditions the black gum loves. Plant out the seedlings in the second spring. To estimate the length of time to a medium-sized tree, you should apply the one foot per year rate.

In a previous issue of Michigan Gardener, mint marigold was mentioned as being able to destroy bindweed and ground ivy. How do I grow it? Is there a better way to get rid of the ground ivy that is overrunning my lawn, garden, driveway, pond, and vegetable patch?

Mint marigold (Tagetes minuta) is a South American herb that grows readily from seed sown directly into the soil once danger of frost is past. It thrives in full sun and will choke out ground elder, bindweed, couch grass and ground ivy as it reaches its full height of six to eight feet. Considered a cash crop in South America for its oil, uses as a condiment and in beverages, it is sometimes considered a weed by others.

If bindweed is a problem in a large sunny area for you, it might be worth a try. However, ground ivy tends to like moist, shady areas as well as sun. For perennial weeds such as these two, there are three types of control: cultural (including crop rotation, such as growing the mint marigold), mechanical and chemical.

As was described in the “Weed Watch” column in the April 2004 Michigan Gardener, to naturally control ground ivy in turf grass, maintain turf density and health through proper culture. Mechanical removal in turf is difficult and rarely effective. Ground ivy is shallow-rooted and it roots at each joint whenever it touches the soil, making it difficult to pull by hand. In beds it can be controlled by diligent and consistent removal. Mechanical removal is accomplished by using a garden fork to loosen the soil about 3 inches deep and gently working the roots out.

To control ground ivy by chemical means, a post-emergent herbicide needs to be used. Pre-emergent herbicides do not work on established ground ivy.

My house faces west and I have a huge maple (I think it’s a Norway maple) in my front yard that shades out what would be the front lawn. The tree roots are very dense and I am having a hard time gardening under it. I would like to replace the lawn with some type of groundcover (low maintenance) and add ornamental and evergreen shrubs as well. Any plant suggestions for this situation?

I appreciate your frustration with the Norway maple (Acer platanoides). A popular neighborhood tree for their dense shade, they also consume great quantities of soil nutrients and water with their heavy-duty surface roots.

You can’t change the nature of the tree, so call a truce on trying to garden directly under it. Make sure any soil buildup or mulch is removed from the tree base and the “knee” where the trunk curves to meet the soil. This smothers the tree’s ability to absorb water and nutrients and fosters trunk and root decay. It also provides a hiding place for detrimental pests and fungal spores.

Rethink your gardening to begin at least 8 to 10 feet out from the trunk of the tree. Since surface roots gradually spread apart as they radiate from the trunk, you can amend the soil in the “pockets” between the roots to accommodate low maintenance plants. By moving substantially away from the trunk, you can also create areas of low berms to give some interest and elevation to your plantings. Remember once the canopy is leafed out, you have predominantly dry shade. This is important when selecting plant material.

Consider variegated and silver leaves when picking evergreen groundcovers and perennials as they brighten up heavy shade. Look for plants that bloom at different seasons. Planting several groups of early-blooming crocus bulbs will give spring interest before the canopy has filled in. However, you can intersperse other shade-tolerant groundcovers such as winter creeper (Euonymus fortunei ‘Silver Queen’), wintergreen (Gaultheria) with its red berries, and lilyturf (Liriope). There are short ornamental grasses, like hakone grass (Hakonechloa macra), blue oat grass (Helictotrichon sempervirens) and blue fescue (Festuca amethystina) with desirable colors and textures. There are a few spreading and low-mounding yews and junipers that a reputable nursery can point out to you. Also consider a hardscape element such as a bench or birdbath to give focus and interest to the heavy shade. There are also a number of shade-loving perennials that will have room to grow if you bring your bed out to the maple’s drip line. By doing so, you will open up your gardening options and plant selection.

I would like to grow wisteria vine. Please provide input on the different species, such as their bloom times, which ones smell the best, etc. Is the American species less aggressive than the Chinese? If so, how aggressive is it? Will I be pruning weekly?

There are two exotic species: Chinese wisteria (Wisteria sinensis) and Japanese wisteria (Wisteria floribunda). American wisteria (Wisteria frutescens) which is a native, is more successful in the southeastern United States than here in Michigan. Although it is cold tolerant to zone 5, you are more apt to find the Japanese here in the north since it will tolerate zone 4 temperatures.

Wisteria is a member of the pea family and climbs by twining its stems around whatever support is available. They’ve been known to consume fences, warp power poles, demolish trellises, and obscure people. All three can reach heights of 25 to 30 feet.

The Chinese is very showy, with flower clusters up to a foot long, which open before the foliage has expanded. The familiar blue-violet blooms appear in early to mid-May but are only faintly scented. There is a white form (W. sinensis ‘Alba’), which is very fragrant. Chinese wisteria may bloom within 3 to 4 years after planting.

Japanese wisteria is aggressive, producing perfect blue-violet blooms on old wood from mid-April to May. Again, depth of fragrance depends on the cultivar you select. Often, you will find the showier the blossom, the less fragrant it will be. ‘Macrobotrys’ (reddish violet), ‘Naga Noda’ (pale violet), and ‘Snow Showers’ (white) all offer significant fragrance.

If you have a sunny and moist site, the American wisteria will produce 6-inch long, pale lilac flowers in June to August on the current season’s growth. Blossoms appear after the foliage has developed. It is a handsome plant in both leaf and flower, showing greater restraint than the Asiatic bullies, according to Michael Dirr, a well-known woody plant book author. Because of the different bloom times, you may want to combine one of the Asian species with the American, although not necessarily in the same location, unless you have steel beams for support.

Whichever species you choose, select a named variety and plant in deep, moist, well-drained, and loamy soil with a soil pH of 6.0 to 7.0. A soil test will determine the pH and if amendments are necessary. The site must get 6 hours or more of sun. Prepare a 2- to 3-foot diameter space for the trunk and add peat moss, compost or aged manure to improve soil aeration and drainage. Wisteria can be trained as a single trunk tree or allowed to climb a structure. It must be supported by a strong pressure-treated wood arbor, pergola, or pole. Young plants should be fertilized annually until they fill the allotted space. Fertilizing encourages vegetative growth so don’t look for blooms. Once established, do not fertilize. Water only if foliage wilts. Both fertilizer and too much water produce green growth and limit flower production.

Certainly not weekly, but some pruning is required to maintain plant quality and promote flowering. Simply keep in mind to single out one strong leader from each main framework branch. Cut off the ends of all new side shoots just beyond the sixth or seventh compound leaf. Do this in summer. In winter, concentrate on pruning back the leader shoots by at least one-half. Cut side shoots to only one or two inches from their base.

It isn’t necessary to be a pruning guru to grow a wisteria of any make or model. Generally the famous frustration of lack of bloom comes from too much TLC—too much fertilizer, too much water and not enough drainage.

How can I eliminate Chinese poppies from my garden? They have become highly invasive and a nuisance even though they are beautiful.

The poppy is in the Papaver genus and while there are none that are known by the common name Chinese poppy, there are some called Oriental, Iceland or alpine poppies. Typically, Papaver plants are not considered invasive although they often reseed given the right climate and placement. It is unlikely that you are having difficulty with invasive Oriental, Iceland or Alpine poppies.

Oriental poppy (Papaver orientale) is the familiar poppy with crepe paper-like flowers that range from 4 to 11 inches in diameter and have dark, shiny black splotches at their base, plus black stamens in the center of the flower. There is a vast array of cultivars and the colors range from white and pastels to shocking reds and oranges. The stems look sturdy but often bend over under the weight of the heavy flowers, especially after a rain. After blooming, in the heat of the summer, the foliage dies back to the ground, leaving a bare space in the garden. Good neighbors to fill in the space in a perennial bed are baby’s breath (Gypsophila paniculata) and Russian sage (Perovskia atriplicifolia). Seeds can be planted directly into the soil and transplanted when young, but they don’t like being moved once their taproot has been developed. Since they resent disturbance, wait until the plants are overcrowded (4 to 6 years) and dig them up carefully and divide.

Iceland and alpine poppies will grow well in our area as biennials or short-lived perennials. Cool summer gardeners get to enjoy how floriferous and long-blooming they are. In cool summer areas, they’ll live for years and bloom practically all seasons. In our zone 5, with the moderately hot summers we have been having, these poppies will bloom in spring and early summer for a year or two before dying, but they usually self-seed before dying out. Iceland and alpine poppies produce ground hugging tufts of light green, hairy, lobed leaves and wiry, hairy, leafless stems of lightly scented, cup-shaped flowers. They bloom late spring through early fall as long as the summers are on the cooler side. The alpine poppies are like miniature Iceland poppies.

As far as the plant you refer to in your question, we believe it could be one of two options. First, it could be the plume poppy (Macleaya cordata). Its countries of origin are Japan and China, so you may have been told that this highly invasive plant is called a Chinese poppy. This plant needs a lot of room because its 6- to 10-foot tall plants spread rapidly by rhizomes and form large colonies. The leaves of the plume poppy are lobed, light green above, and gray-green beneath. The young plants are particularly handsome with cream-colored flowers held in long plumes at the top of the plants in early to mid summer. 

If this is indeed the plant you have, you have some work to do to eliminate it. Deadhead religiously and don’t allow them to reseed. Mulch the bed heavily with soaking wet cardboard and keep replenishing it. Dig out the volunteers and get the roots. Do not put them in a compost pile. This could be an ongoing battle for two to three years.

If the plant you are talking about is not tall, then the second option would be a wood poppy or celandine poppy (Stylophorum diphyllum). These are beautiful plants in a woodland setting, as they provide bright yellow, early spring flowers even in heavy shade. They have light green, deeply cut basal leaves and the flowers are 1 to 2 inches wide. They look beautiful with Virginia bluebells and both die back when finished blooming. These plants are prolific re-seeders and can become significant in numbers in three to five years. If this is what has happened, the best way to decrease the population is to pull them up when they emerge and not allow them to re-seed. The good news is that they are relatively easy to pull out of the ground, roots and all.

I have a shady backyard (mostly maple trees). Are there any ornamental grasses that will grow there?

There is quite a variety of ornamental grasses that will grow in the shade. Not as bold, big, tall and dramatic as the sun-loving ones, but certainly equally beautiful. They are easy-to-grow plants that fit nicely into the more serene and subtle nature of a shade garden. Some are tolerant of drought conditions, which you might have under your maple trees. For most it would be good to supply at least an inch of water per week. Here are some ornamental grasses that do well in the shady garden:

Hakone grass (Hakonechloa macra ‘Aureola’). This attractive grass is one of the best for shade. It has striking gold variegated leaves with an attractive habit of falling over to one side. This plant makes a lovely companion to hostas.

Palm sedge (Carex muskingumensis). This sedge spreads to create a low maintenance groundcover for moist, shady locations. The light green leaves resemble palm fronds at the top, which gives it its common name. Grows about 2 feet tall.

Bowles’ golden sedge (Carex elata ‘Aurea’ or ‘Bowles’ Golden’). Has attractive lime-green leaves in early spring and makes a lovely companion to gold variegated hostas. Grows 2 feet tall and prefers moist shade.

Silver variegated Japanese sedge (Carex morrowii ‘Variegata’). Has white leaf margins and grows 12 to 18 inches tall. It likes morning sun or part shade.

Variegated sedge (Carex morrowii ‘Ice Dance’). This semi-evergreen sedge has green foliage edged in pure white. One of the newer grasses for shade, it spreads to create a low-maintenance groundcover in the shade garden.

Plantain-leaved sedge (Carex plantaginea). Grows 6 to 12 inches tall and has green leaf blades that are wider than most sedges. Among the grasses for shade, this is one of the best for tolerating dry conditions. It makes a nice companion to ferns and North American woodland natives.

Northern sea oats (Chasmanthium latifolium). Grows about 3 feet tall. It has dark-green, bamboo-like foliage and attractive dangling flowers in mid-summer. This grass can take quite a bit of sun and sometimes can self-seed excessively, so remove flowers in late fall. (The flowers can be used in fall cut-flower arrangements.)

Snowy woodrush (Luzula nivea). A clump-former, it grows about 18 inches tall and is evergreen, with light green leaves and clustered white flowers in May to June.

Greater woodrush (Luzula sylvatica). This evergreen, clump-forming ornamental grass has green foliage covered with silky hairs. It grows about 2 feet tall and flowers in late spring into early summer. It prefers moisture and light to medium shade, but is quite drought tolerant. It is tolerant of most soils. Makes a good companion to ferns, shade-loving wildflowers and shrubs.

I see the term “frost-free date” used this time of year. What is the frost-free date for southeastern Michigan and what exactly does that mean?

Frost-free dates are a scientific best guess to determine when you will be able to plant out annuals or any other tender plant without the likelihood of those plants being killed by a frost. Michigan State University has published a table of dates based on a thirty-year average (1951 to 1980) that gardeners can use to determine these dates in their local community in Michigan. To use an example, the published dates for Pontiac’s 30-year average date of the last 32-degree temperature is May 24. This means that it is statistically safe to plant on or after May 24 in the Pontiac area and not experience a low temperature under 32 degrees.

This date is not a guarantee, only a statistical calculation based on historical data. Many gardeners choose to plant earlier and are able to protect their tender plants with coverings on any night when the weather is predicted to drop to near freezing or below. However, planting early is often unnecessary work, as plants placed into warmer soil with warmer night temperatures will grow with enough vigor to match the growth of the earlier transplants very quickly. The old adage, better safe than sorry, can also mean less work to produce the same vigorous plants.

If you would like the exact statistics for your community, visit the website at http://climate.geo.msu.edu/climate_maps.html and click the map on the spot nearest to your Michigan gardening location. Frost-free dates in southeastern Michigan vary by location. On the website you will also find a myriad of weather and climate information that may make your gardening easier, or at least more scientific.

According to a soil test, I need to lower the pH of my soil. What are the best and safest ways to do that in an area where I want to grow vegetables?

So you’ve decided on a spot for your garden and have an idea of what you want to grow. That’s a great beginning. Wisest of all, you’ve tested your soil, specifically its pH, so you know which plants will grow best in that bed. Most plants prefer a soil pH somewhere between 6.5 and 7.2. The term “pH” comes from the French term pouvoir d’hydrogene which means “hydrogen power.” It is the amount of hydrogen ion concentration in the soil sample that is measured on a scale from 0 to 14; zero being the most acidic, 7 neutral, and 14 the most alkaline. The pH scale is logarithmic, meaning that each number on the pH scale actually represents a tenfold change. For example, a pH of 7 is ten times more alkaline than a pH of 6.

You can lower your soil’s pH (making it more acidic) by adding chemicals such as soil sulfur, iron sulfate or aluminum sulfate, adding an acid-type fertilizer, or by working organic mulches into the soil such as peat moss, oak leaf mold, composted animal manures, sawdust, ground bark, decayed pine needles, or homemade compost among others.

Organic mulches are likely to be your safest pH-adjusting additives. They not only cover and protect the soil, they also release substances that feed earthworms and other helpful soil organisms. These organisms release nutrients into the soil so that plant roots can absorb them.

Would you please advise me how to prune azalea bushes and yews. They are very old – I am guessing approximately 45 years, since they were here when we moved in 31 years ago. My husband has always trimmed them using electric shears and has only trimmed the top of the shrubbery, hence, all of the foliage is at the tips with a lot of wood at the center. Can I salvage these shrubs by pruning them back drastically? Will I lose them if I do so?

Shearing your evergreen shrubs will give them a neat, formal appearance, but when done year after year it can create undesirable and unhealthy results. Two different pruning methods are listed below for yews and azaleas. When used for evergreens, these pruning methods are best done before bud break in the early spring.

Renewal Pruning: Best used when shrubs are older and have become overgrown with large amounts of unproductive wood.

Method: Cut off the oldest branches near ground level leaving only productive young stems. If there are only a few young stems, remove the oldest branches over a three-year period. Prune back 1/3 of the oldest branches each year to allow even light penetration for new growth. When new shoots develop they can be thinned back to various lengths, which will develop strong branches.

Cons: More pruning cuts have to be made over a longer period of time.

Pros: Shrubs look aesthetically better during the process. Weakened shrubs have a higher survival rate when using the renewal rather than the rejuvenation method of pruning.

Rejuvenation Pruning: Best used when shrubs are unhealthy and severely overgrown.

Method: Cut all branches 6 to 12 inches from ground level. This is a drastic method and better results are achieved if followed up with proper watering and fertilizing practices.

Cons: If you are pruning a flowering shrub you could lose bloom for 1 or more years. If the shrub has been in decline for several years it may not recuperate.

Pros: Strength and vigor of new shoots are directly proportional to the amount that the stem is pruned back.

General pruning tips:

• Use clean, sharp pruning tools appropriate for the task.
• Remove dead, broken or diseased branches any time of the year.
• Yews are a better candidate for rejuvenation pruning.
• Azaleas are a better candidate for renewal pruning.
• Always check the mature size of the shrub before planting; a properly-sized plant will require less maintenance pruning.
• When shearing your evergreens always continue to make thinning cuts every season to allow for light penetration and inner growth.