What is full sun?

Bernadette Vangool/Submitted. The best time to measure the sunlight in your yard is during the active growing months.

By Bernadette Vangool – Saskatchewan Perennial Society

‘On a given day, only the uppermost leaves on the tallest trees enjoy the luxury of direct sunlight from daybreak to nightfall. Most plants simply have to tolerate some period of shade during the growing day.  From a gardening perspective, the definition of ‘full sunlight’ is therefore described as a block of at least six hours of direct sunshine during the mid-part of the solar day. Anything less is partial shade, meaning a plant’s growth and productivity is reduced unless they are among the ‘shade plants’ that have evolved various mechanisms over the millennia for capturing and using sunlight more efficiently to compensate for life beneath a canopy.’
                                                                                                                                    Brian Baldwin

This column was inspired by one written by Brian Baldwin, one of the early submissions by the Saskatchewan Perennial Society and published in 2007. Brian was well known by the horticulture community for his sharp wit, as a teacher and as a writer of all things horticulture.  He left us too soon, in 2009, but is fondly remembered by many.

The intensity of the sun changes over the seasons. The sun is much lower in the sky at the end of August, resulting in very different shade patterns in our landscapes. The best time to measure the sunlight in your yard is during the active growing months, after the trees have fully leafed out. In Saskatchewan that would be June and July. Observe and record the light in different planted areas over several days. A quick look out the window at each hour of the day, should suffice to give you a pretty good idea of which areas receive full sun. Six to eight hours for perennials and flowers and eight to ten hours for the vegetable garden.

Now for some more terms, that may or not be interpreted the same by gardeners. “Part sun”, or “full sun to part shade”, I would interpret as four to six hours of sunlight with most of those hours being in the afternoon when the sun tends to be hotter. If these are sun-loving flowering perennials, the more sunlight provided the more flowers you can expect.

Place plants that do best in “part shade” in the morning sun, with an exposure of three to six hours of direct sunlight.

“Full shade” plants can be placed under tree canopies. They still need some dappled light to thrive. Deep shade is seldom conducive to healthy growth. In my yard, I mulch deep shade areas and plant my shade loving plants around the drip-line of trees. No amount of fertilizer is going to make plants thrive in the dark. (except perhaps some hardy dead-nettle or Lamium). Full shade plants can tolerate some sun in the morning or late afternoon, but seldom do well in mid-day sun.

Some areas on the north side of buildings, may be consistently shaded, but still receive an abundance of reflected light. This is especially true of those planted adjacent to light coloured buildings. Reflected light anywhere in the landscape is difficult to measure and can make a large difference in which plants will do well in a specific area.

No matter what the labels say, many plants are quite flexible. Over time you will become quite adept at choosing just the right location for individual plants. If leaves are curling up in the middle of the day, or the flowers on certain perennials are sparse, just moving them to another spot in your garden may be all that is needed. Make sure any such moves are done on overcast days, and water the transplants regularly. Treat them as newly acquired perennials, that need extra care until established.

Of course, light is not the only consideration when thinking about your plants well being. Good soil with lots of nutrients and adequate water, especially for those perennials close to large trees, (very adept at robbing moisture from their smaller cousins) are very important. This column is provided courtesy of the Saskatchewan Perennial Society (SPS; saskperennial@hotmail.com ). Check out our website (www.saskperennial.ca) or Facebook page (www.facebook.com/saskperennial).