Knecht's

The establishment of the highly destructive emerald ash borer in Minnesota will once again force us to re-evaluate what type of trees we should be planting.  When Dutch Elm Disease devastated our urban and native forests starting in the 1950′s the same question was asked since so many communities had planted such large numbers of Elm trees.

The all too frequent answer to this question between 1960 and 2005 was to plant large numbers of ash trees.  Seedless Ash varieties were available and ash were easy to grow in tough urban conditions.  The results were the over-planting of ash trees, and great vulnerability to another disease or pest.

Planting so many ash trees was simply foolish and ignored the hard lesson learned of Dutch Elm Disease.  Our response to the havoc being created by Emerald Ash Borer should be to plant a wide diversity of trees so if/when another devastating pest or disease comes along, we will lose a far smaller percentage of our urban forests.

When considering choices for shade trees, try to get a fairly even balance from the following families of trees:  Oaks, Maples. Lindens, Hackberry, Birch, Horsechestnut, Ironwood, Yellowwood, Catalpa, Honeylocust, Ginkgo, Maackia, Aspen, Kentucky Coffee Tree, Amur Corktree, Locust, Willow and the many good new hybrid Elm varieties that are highly resistant to Dutch Elm Disease.

When considering Ornamental trees, try to achieve a balance from the following groups:  small Maples, Flowering Crabs, Magnolia, Cherry, Plum, Lilac, Hydrangea, Forsythia, Ninebark, Euonymous, Bleu Beech, Pagoda Dogwood, Hawthorn, Weeping Pea Shrub, dwarf evergrens of various kinds, dwarf or narrow form Birches and Oaks, small Willows and the native Showy Mountain Ash.

As you can see there are plenty of options available in both shade and ornamental trees to help us avoid over-planting of one kind of tree.  Be sure to make your choices to the varieties best suited to your particular site conditions of soil type, light availability, drainage, amount of space available, slope, possible pollution, presence of utility lines/other obstructions, and the regulations in your local unit of government.

If finding the right tree seems a bit challenging, you may want to stop by the nursery for some professional advice.  Make your mind up to enjoy variety.  Viva la Difference!

 I am also sharing this post with my web blog for the Northfield News.

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I will also be sharing some of my blogs for blog entries at the Northfield News.

To prevent the transmission of diseases such as Oak Wilt and Dutch Elm Disease, it is best to prune these varieties during the late fall, winter and very earliest part of spring. Up until about April 7th, you should be pretty safe pruning, and not have to worry about the beetles that transmit these fungus diseases visiting the fresh pruning cuts.  The beetles become active in mid to late April.

Once active, the beetles spread fungus disease by visisting an infected tree first, and getting fungus spores on their bodies.  They then move to a healthy tree where they are attracted by fresh wounds to the tree bark, where the fungus spores spread from the beetle to the vascular system of the tree that is vulnerable due to a fresh cut through the bark.  Normally, within a few days to a week after a fresh cut or broken branch, the broken ends of the sap carrying tubes in the tree bark seal shut and disease transmission is much less likely.

 If you prune your Oak or Elm tree now, prior to April 7th, the cuts should naturally seal off as the sapwood dries a bit around the edges of the cut, and the trees will be relatively safe when the beetles become active later in April.  Another tree variety that is best pruned in cool weather is the Thornless Honeylocust.  Bark cankers are much less likely to establish if pruning is done before canker organisms become active during warm weather.

Plant Spotlight:     Pussy Willow.  A sure sign of spring is the delightful emergence of the soft furry catkins on pussy willows.  Branches can be cut before or during the process of emergence, and placed in a vase with water to decorate, and give your home that fresh spring feeling.  Common Pussy Willow, French Pussy Willow, Giant Pussy Willow, and Black Pussy Willow can all be very nice to add this spirit of spring to your home.

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