 |
Arboriculture - Part 2
Gardening with trees |
Shade gardens are a delight to create. Your palette is full of shades of green - from moss to chartreuse. But you are not limited to green. Shade loving plants can don the white apparel of certain lamiums and hostas or bear the sanguine raiments of purple palace heucheras and burgundy lace maples. While perennials tend to bloom for shorter periods in the shade, the intensity of their colour is enhanced in the subtle lighting provided by mature trees. Brilliant triullium, astilbes, ligularias and many more brighten shady corners of my garden for brief but breathtaking periods. Annuals can add almost garish extremes to a shade garden. While dainty begonias and impatiens can add dapples of daily cheerfulness, exotic arisaema (Jack in the pulpit) can be real eye stoppers. Larry Hodgson's book Making the Most of Shade is one of many great books to help you design your masterpiece.
But what of the trees that make it possible? It is important to understand a bit about the needs of these gentle giants. Most people do not realize that 80–90% of a trees roots run close to the surface - within the top 60 cm of soil They spread at least as far as the canopy width and often well beyond. While some species of trees easily accommodate planting beneath their canopy, others do not.
It is usually recommended that we add soil when creating a shade garden under an established tree. However, changes in soil level (or grade) can suffocate tree roots. Trees like silver and red maples, Colorado spruce and green ash are fill-tolerant. This means they can tolerate additions of as much as 15 cm (about six inches) of soil. However, trees like sugar maple, white pine and linden are fill-intolerant. Try not to build soil up close to the trunk of any tree as this can cause bark to rot and the flow of nutrients in the tissue beneath the bark to cease. Rather than building up soil under fill-intolerant species, use well spaced clay pots and create a container shade garden. Planters can provide bursts of color and interest while not imperiling the tree roots.
While fill can suffocate roots, root disturbance through cultivation or digging can also harm your trees. As with fill, sensitivity to disturbance varies with species. The American elm can tolerate extensive root disturbance. Such trees can have over 25% of their root mass removed and still survive. Others, like oak and cottonwood, are extremely sensitive and minor disturbances can have long term impacts. Trees suffering from root disturbance may display leaf scorch and die back. If you notice your tree is unwell, avoid further root damage. Careful pruning may help the tree to recover. Consult an arborist if you have real concerns. Well cared for trees will enhance your property and provide you will wonderful gardening opportunities.
May toads nestle in your flower beds and help you tend your beauties in the spring.
Resources and References (sorry I didn't have time this month to extend these)
(Peter Crow, 2005, Forest Research, Influence of Soils and Species on Tree Root Depth).
NDSU Plant Pathology Diseases of Trees http://www.ag.ndsu.edu/pubs/plantsci/hortcrop/pp697-1.htm
Ohio State The Response of Native and Naturalized Trees to Construction Activity http://ohioline.osu.edu/sc152/sc152_12.html
Wiki Shade of Green http://en.wikipedia.org/wiki/Category:Shades_of_green