Question
Dear Mark

I am designing a very large rectangular garden 100 meters x
40 meters. I want to plant trees around the whole garden
wall in order to shelter the garden from outside elements.
I want to plant the trees as close to the outside wall as
possible. What trees would be most suitable and least
damaging to the wall? The weather is very warm and sunny in
the Spring and Summer time but very cold in the winter.

Answer
Hello,

For a windbreak use a combination of evergreen and deciduous trees and shrubs.   On the side of the prevailing winter wind (typically northwest),use evergreen plantings such as arborvitae,junipers and spruces.  On the south side use deciduous trees such as cottonwood,silver maple,hackberry and green ash.  Slower growing deciduous trees include; red oak,bur oak,white oak,black walnut and white ash. Deciduous trees on the south side will allow winter and spring sun in to warm the ground.  This list is a suggestion only.  Check with a nursery for varieties suitable for your area.
Do not plant one variety of plant of either evergreen or deciduous in the windbreak.   Mix two or three varieties together.   This is useful in case disease strikes. If disease strikes,it will most likely effect one of the plant species and thus the chances of the entire windbreak being destroyed will be lowered.

The windbreak protection zone extends 8 to 10 times the height of the windbreak trees.   From the dimensions you gave,this means the trees should on average about 15 to 20 feet high.   If you have space,use a two or three row windbreak.  This will be more effective in breaking the force of the wind.  You might also consider planting a row of shrubs up to about 50 feet from the windward side of the windbreak to act as a snow drift barrier.  Position the trees as perpendicular to the prevailing wind as possible.  The length of the windbreak should be ten times greater than the height to minimize air turbulence around the windbreak.

One Row Windbreak:

*  For field or orchard protection,snow trip or in urban setting with little space;uses little land;limited value to wildlife.

*  Densely planted for maximum effect.

*  Maintenance and replanting essential to avoid gaps from dead or weak trees.

*  Use shrubs,dense evergreens that retain lower limbs and foliage,such as junipers,spruces and arborvitaes (for moister sites) ,or densely branched deciduous trees,preferably with narrow crowns.

Two Row Windbreak:

*  For field or orchard protection,barn or urban setting;some wildlife value.

*  Densely planted as with 1 row above.

*  Twin row high density has trees planted alternatively,with a spruce in one row,filled by a tree in the other row; rows close together; use junipers,spruces and arborvitaes (for moister sites) or austrian pine.

*  Standard two row (two rows separated by a space) uses two rows of dense evergreens (juniper,etc..) or one evergreen and one shrub or deciduous tree row.

As long as the root spreads are kept away from the wall no damage should occur to the wall.  Good luck.  Write back if you have further questions.

Mark  Harshman
http://www.mahdrafting.com
Email: [email protected]

http://www.scribd.com/markscrib47