Did you know that a shade tree will provide us with lower temperatures of between five and 12 degrees Celsius than if we were out in the blazing sunshine? No wonder we migrate naturally to the shade to read a book, have a picnic or take a nap. Trees not only provides shade; the moisture that they transpire has a cooling effect.
A shady deal
Now is the time to begin thinking about what goes on under your trees and on the north side of your house, where you will find some interesting opportunities to plant a ‘shade’ garden.
The following is our short list of favourites for dappled shade, plants that prefer a sun/shade mix. They generally do not like the hot, dry mid-afternoon sun.
Astilbe
Also known as False Spirea and Feather Flower, this plant provides vivid colour for a long stretch of time, beginning in late spring right through the summer. The 30- to 80-cm-high blossoms are always a delight and the colours almost look plugged-in or electrified in their intensity. They like to grow in an open, peaty soil. Once they dry out, they do not rehydrate well, so to prevent drying, be sure to mulch with five cm of shredded cedar bark.
Rhododendrons
Rhodies, as they are affectionately known in the business, have a special place in the shade garden. They love an acid soil, which is opposite to the alkaline stuff most of us put up, if you live in Southern Ontario. Always plant your rhododendrons in an open, sandy soil mixed with finely ground-up pine bark, about 30 per cent by volume.
Add about four tablespoons of garden sulfur every six weeks throughout the summer and early fall to help acidify the soil. Keep in mind that you are not fertilizing them per se; you are changing the pH of the soil.
For fool-proof garden performance, we recommend the winter tough ‘PJM’ varieties if you live in Ottawa.
Boxwood (Buxus)
Here is a broad-leafed evergreen that performs very well in Ottawa and Montreal. Since boxwood is an evergreen, treat it as such with a humus-based soil of peat or compost, and fertilize with an evergreen food such as 30-10-10 every month or so until the middle of the summer.
Check out the many boxwood hybrids that have been introduced over the years. You will get a deeper colour and more finely textured foliage with these versus the original version of Korean Boxwood.
Oregon Grape (Mahonia aquifolium)
Native to B.C., this plant features holly-like leaves that remain on the plant all winter and are replaced each spring as new growth occurs. They have a delightful yellow flower in spring and a dense, shrubby growth habit. Oregon grape matures to about one metre or so high and equally wide. We like it best when planted on the fringe of a hardwood bush or under the shade of tall deciduous trees and shrubs.
Now, about those shade trees
If you have trees on your property that were planted within the last three years, watering is of critical importance this time of year. A mature 20-metre-high maple tree transpires over 500 litres of water on a hot day. That is why it is important to get water on its roots this time of year.
Apply water to the root zone of your young and mature trees by placing a hose at the base of the tree with just a trickle of water coming out at the end of it. Leave it there for three or four hours. The water needs to seep deeply into the root zone for it to be of any benefit.