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I planted a silver mound in mid-August. As of late September, it wasn’t very big (about 8 inches), but it is already “flopping” (i.e. parting in the middle). Why is this and what can I do to prevent it? The plant is in full sun.

It sounds like a case of too much of a good thing. Silver mound (Artemisia) tends to get leggy and flop in the humidity of our summers, especially if grown in good garden soil. Relocation to an area of sandy, lean (nutrient poor), and fast-draining soil in full sun should postpone the flopping next summer. However, silver mound can still separate by late summer if allowed to get too large. If this occurs, it can be sheared back for fresh growth.

Late this summer, the top vertical stem of our white pine turned brown and died. The balance of the tree remained healthy. In the fall, the brown began moving down the tree. This tree is about 7 years old and sits at the edge of our woods. It has eastern exposure with acidic soil. I am not sure if the sprinkler system hits it. When we first saw the top stem turning brown, we watered the tree several times with a Miracid. Earlier in the summer, we lost a white pine that started with these same symptoms. Is there anything we can do to save this tree?

Seeking the services of a certified arborist will be your best defense against losing your tree because it is exhibiting symptoms that can be caused by more than one problem. An insect, the white pine weevil, bores into the terminal shoot causing death of that branch. The weevil rarely kills the whole tree, but places it in a weakened state where the attack of other insects, diseases, or environmental problems can cause gradual death.

Eastern white pine (Pinus strobus) is a fast-growing tree. Unfortunately, as they mature, many develop problems. The symptoms reported are a general off-color, yellowing or browning of the needles, stunted growth, stunted needles, or total browning of the tree followed by death. The cause for the decline is most often due to environmental stresses rather than a particular pest. The stress opens the door to secondary attacks by diseases and insects, which then accelerate the decline of the tree. Stress is the primary problem because it weakens the tree’s natural resistance.

Location of a white pine tree is very important for proper health and vigor. White pines require well-drained, deep, fertile, acidic soil with a moderate amount of moisture. They do not tolerate poorly-drained soil, high pH, compacted soil, a thin topsoil layer, buried debris or drought. Any other conditions that restrict root growth are also detrimental to white pine trees. Root diseases and cankers are the most common fungal pathogens that attack the Eastern white pine. Root disease symptoms are characterized by overall poor growth, the tree becomes off-color, wilts and dies.

Insects often act as vectors (transporters of the pathogen) for diseases. They breed in the dead trees and stumps. Then the new generations move to the surrounding stressed trees, bringing the disease with them. Other attackers of stressed white pine include the pinewood nematode, which feeds on vascular tissue in the branches and trunks of all pines and some other conifers. An insect called the pine sawyer beetle acts as a vector for the nematode, introducing it to healthy trees. Damage from the pinewood nematode is seen as sudden wilting and death.

When Eastern white pine trees decline they should be removed quickly so they do not act as breeding places for insects that spread diseases to surrounding trees. Replace dead trees with other evergreens that can better tolerate the existing site conditions.

I have a large tulip tree; the roots of this tree were damaged during a fence installation. Subsequently the tree developed slime flux and many branches died. I have kept the tree well-watered and fertilized, and it appears to be recovering and making much new growth. When would be the proper time to remove the dead branches from the tree? They are unsightly and some are quite large and could damage structures if they fell.

The tulip tree (Liriodendron tulipifera) is not a tree for residential property. Many times we as gardeners just cannot help ourselves and purchase or inherit a tree that struggles where it is planted. The tulip tree needs a large, open area to grow and develop its branches and root system to display its real beauty and remain healthy.

You are taking the correct steps to insure the health and longevity of your tree after its injury. Since there are no curative or preventive measures for slime flux, you are correct in practicing IPM (Integrated Pest Management) to maintain the tree in a state of vigor by using a consistent watering and fertilization program and minimizing future wounds or injuries.

The best time to prune off the dead limbs would be in the tree’s dormant season, leaving less chance to spread the disease. When pruning, use a 20 percent bleach solution in water to dip and wipe your tools when changing cutting areas. This procedure will stop the spread of the disease from infected tools to healthy tree tissue.

Lastly, please investigate all the symptoms of slime flux to confirm your diagnosis, as this bacterial disease does not usually affect tulip trees in our area. Other diseases and insects are more likely to cause a problem showing some of the same symptoms, like aphids, which secrete large quantities of “honeydew” (a clear sticky substance). Unlike slime flux, however, there is a treatment program for aphids.

What is killing the hop hornbeam trees? I have lost mature trees and there are several more that are dying. I have also seen sick trees along 7 Mile in Northville and at Ford Field in Northville. Can this be related to the emerald ash borer?

Hop hornbeams are in the birch tree family. The pattern of destruction is very similar to the emerald ash borer’s (EAB) attack on ash trees. Unfortunately it appears the bronze birch borer has infested and is decimating the hornbeams. Not only are birch borers very similar in size and shape, but their life cycle pattern mimics the notorious EAB. However, birch borers are native to North America, occurring throughout Canada and the U.S. to as far south as Maryland to Utah. They are not an alien introduction.

The first symptom of infestation is the dieback in the upper crown. This progresses to twig and branch dieback. Trees may take several years before dying, although they may die during a single year if conditions are optimum. The tree’s decline may be reversed in the early stages but not likely if more than 50 percent of the crown is damaged. The birch borer also mines extensive tunnels through the inner tree tissue like the EAB. When the weather cools, as is typical in a Michigan autumn, the larvae stop feeding and overwinter in the tree. Because of prolonged adult emergence and the long egg-laying period of this insect, all larval stages can be present during winter, from newly hatched to fully grown.

To reduce the number of adult borers, recently killed or heavily infested trees should be cut down and destroyed. This limits the adults emerging in spring. Prune out dead and dying branches slightly below the point of dead wood. Insecticides can be applied to the surface of the tree bark to kill larvae emerging from eggs. Sometimes as many as three applications are required from mid-May to mid-July to handle the repeated hatchings from the staggered egg laying. Vigilance, control, and integrated pest management are the only real tools against this destructive insect.

I have purchased iris that say they are reblooming. Why don’t they rebloom in the fall?

There is a wealth of interest in reblooming iris. The traditional iris blooms only once, in the spring, and goes into summer dormancy. Hybridizers continue to work on iris that bloom multiple times during the year. Most rebloomers bloom in the spring and then again in summer or fall. There is even a group called “everbloomers” because they bloom constantly, until frost, if the conditions are right.

Rebloomers are almost as easy to grow as the ordinary iris. They need well-drained soil and to be fertilized in spring as well as after the spring bloom with a fertilizer that is fairly low in nitrogen such as a 5-10-5 mixed 50/50 with superphosphate. You don’t want them to go into dormancy after blooming the first time, so continue to water during dry weather. Ordinary iris can be planted under shade trees because they only need sun before they bloom in the spring. Rebloomers need at least a half day of sun all year. These reblooming varieties are said to be more resistant to rot, more vigorous in growth, with less spot and insect damage.

As fall approaches, cut off all flower stalks with buds and bring them indoors. Cut the remaining foliage to the ground. Uncut stalks usually freeze and fall over, causing rot. These reblooming iris increase faster than the standard iris and may need to be divided every second or third year.

We are looking for a slightly unkempt or cottage garden look at our home, yet need it to be low maintenance. There is sufficient room to tier large plants; we would like evergreens stepped down to flowering deciduous shrubs with trees interspersed. We would love a white birch, but don’t want to use all the chemicals we’ve had to with past birches. Any ideas for a substitute, or are there hardier, less insect-prone white birches?

We already plan on sunburst locust, beech and tri-color beech trees, dogwoods & Japanese maples. Any suggestions for flowering shrubs other than potentilla, wiegela, forsythia and lilac? We are trying for continual color.

An effective way to have continual color in your garden would be to not make your selections solely on a plant’s flower, but more on its ability to have multi-seasonal appeal. Since you’ve stated that you have sufficient room, adding both multi-seasonal shrub choices as well as keeping a few single-season plants like the lilac and forsythia may suit your needs. I would suggest adding some of the smaller spireas (‘Neon Flash,’ ‘Goldflame‚’ etc.), Fothergilla, viburnums, Clethra and witch hazels to name a few.

As for the white birch, unfortunately there isn’t a good white-barked substitution. However, the river birch ‘Heritage’ (Betula nigra ‘Heritage’) is an excellent alternative. Red maple (Acer rubrum, clump form) is also a good substitution for the unique, 3-pronged birch silhouette.

I have a couple poke weeds, but very much want more and I have plenty of space to grow them. Do I remove the flesh from the berries? Is stratification necessary? I am guessing that the birds like the berries so much that I never have more than a couple plants. Although at one time, I did have more when they were growing in the shade.

It has been my experience that the easiest way to grow pokeweed is to not want to grow pokeweed. However, if you have your heart set on a grove of Phytolacca americana (or Yoshu-yamagobo as it’s known in Japan) this information from the University of Florida’s Cooperative Extension Service may help:

Pokeweed may be grown from seeds in the following way. Gather about a pint of the purple berries, crush them, cover with water, and let ferment for a few days. The good seeds will settle to the bottom and the pulp and skins can be floated off and discarded. The seeds are then spread out to dry and then stored in a cool place. When it’s time to plant, the seeds can be soaked in concentrated sulfuric acid to break dormancy and speed germination. After 5 minutes the solution is poured off and seeds are washed thoroughly in running water. The seeds are again dried and are then ready for planting. The seeds should be sown early in the spring in rows 4 feet apart. The seeds should barely be covered. Finally, the seedlings are thinned to about 3 feet apart in the row.