By Virginia Stephenson, Master Gardener
Light is a very important consideration when choosing plants for your garden and when choosing where in your garden to place them.
All plants have optimal light conditions under which they will grow, thrive and bloom. Fortunately, the question of light requirements has been simplified for us, and most plants have been categorized into one of three groups requiring full sun, partial shade or shade. This information is generally included on the tag accompanying the plant.
Full sun, does not mean that the plant must be in the sun from the time it comes up until the time it sets. Full sun is defined as 6-8 hours of direct sunlight per day. Part sun or part shade is usually defined as 4-6 hours of sunlight, and shade or full shade is an area that receives less than 4 hours of direct sunlight per day. It should be noted, that within the group of full sun plants, some will prefer, the weaker morning sun, while others will prefer the hotter afternoon sun, and they should be placed accordingly.
The question of where in your garden to place each of these groups of plants can be considerably more complex. While some gardens are sunny, and others shady as a whole, many gardens contain a mixture of sunny and shady areas. The problem arises from the fact that the light patterns in your garden are not static, but are in fact ever changing. They change hour to hour, as the position of the sun in the sky goes from east to west, season to season as the position of the sun moves from south to north and back again. If your shade is from deciduous trees, light changes as the trees produce and lose their leaves and as they grow. If there is any type of man-made structure there will be an ever-changing pattern of sun and shade, which will vary throughout the day and over the course of the growing period.
Not all shade is created equal, and the type of shade will depend on the nature of the object which is obstructing the sun’s rays. Deep shade is the type of shade found under evergreen trees, or in the shadow of buildings where all light is blocked. Dappled shade is common under deciduous trees. These trees will create a patchwork of shade in summer, but may allow almost full sun in autumn and spring. Partial shade is common in most gardens, which will have areas that get sun for only part of the day.
Added to the fact that the light patterns are continually changing, we may also have misconceptions about where the sunny and shady areas are located in our gardens. People tend to be creatures of habit, and if one habitually goes into the garden around the same time of day, what we perceive as the sunny and shady areas of our garden, may not be in sun or shade earlier or later in the day.
My yard contains a variety of mature trees, and there is no area in my flower beds which is not in shade at some time during the day. This is actually quite nice when working in the garden during the summer, as there is always a shaded area in which to work out of the sun. But it does limit the option of growing plants that require full sun. Some of my flower beds are literally under trees, with the tree growing within the bed, and were therefore, I assumed, shade gardens. It was here that I first discovered the fallacy of my thinking. Having planted a shade loving plant next to a tree in one of these beds, I was surprised to find it burned and obviously suffering from too much sun. While moving the plant to a more suitable location, I began to look more carefully at the patterns of sun and shade in my yard, and began to rethink some of those common sense notions under which I had been operating. I discovered that some of those areas under the trees actually received quite a bit of sun, possibly even enough for full sun plants. I realized that at our latitude, in the summer the late afternoon and evening sun shines from the north-west, and illuminates northern exposures. I found that the garden beds along the eastern wall of the house did not get the early morning sun. Although there are no trees within fifty feet of that bed, there are trees on the eastern and southern edge of the yard, and these trees which are up to 60 feet tall, block the sun as it rises, until later in the morning when it is high in the sky. I also discovered that the raised bed on the south wall of the garage, which I had always considered to be my sunny garden, was in fact three distinctly different areas. The center portion is a full sun area, while the western end of the bed, due to the afternoon shade from the house is a partial shade area. The eastern end of the bed, due to a combination of sun blocking elements receives almost no direct sunlight, and is a full shade area. Attempting to grow continuous massed plantings of the same flower combinations from one end of the bed to the other proved to be unreasonable, and doomed to failure.
So what can one do to unravel all of this complexity, and find the proper areas in which to plant each category of plants? The answer is the creation of a sun or light map of your gardens. The process is relatively simple, but somewhat time consuming, and may require the sacrifice of some early morning sleep. Start by making a map of your yard with the various garden beds drawn in, and numbered, lettered or otherwise named. In the case of large garden beds, you may wish to divide them into smaller areas on your sketch, where differences in the amount of sun or shade may occur. Then prepare a spread sheet, with the various garden areas listed down the left hand side. Across the top of the spread sheet write in the time of day from sunrise to sunset, dividing it into hourly segments or whatever shorter or longer time segments seem most reasonable to you. Then chose a sunny day, and spreadsheet in hand, observe each of the garden areas listed on your sheet, at the times listed on the top of the sheet. For each area you have listed, mark on your sheet whether it is in sun or shade, at that particular time of day. At the end of the day, tally up the total time that each area was in the sun. The number of hours of sunlight in each area will identify it as a full sun, partial sun/shade or full shade area. You can now add this information to your garden map, turning it into a sun map of your garden. This map can then quickly show you the most appropriate choices for the placement of your plants, in accordance with their light requirements. Your plants will thank you, and you will experience more success with your plantings.
Your sun map can be as simple or as detailed as you chose to make it. You may chose to map your entire yard, or only certain garden beds with more changeable light patterns. You do not have to make all your observations on one day, but could spread them over several days. You probably do not have to get up at dawn to begin your observations, but can extrapolate backwards, unless you are dealing with particularly complex and variable light patterns. In addition, if your purpose is to identify the full sun areas of your garden, you only need to identify 6 – 8 hours of sun exposure, out of the possible 17 hours of sun that shine on Winnipeg around the time of the summer solstice.
You do have to keep in mind however, that the patterns of sun and shade change throughout the growing season. If possible you should repeat your observations, at least three times: at the beginning of the growing season, at some point in mid season, and again toward the end of the season, comparing your results to see if they affect the light designations of your various garden areas. Rechecking your sun maps from year to year will enable you to keep your knowledge of your sun and shade areas current and useful.
So go ahead, do a little garden sleuthing, and record some observations. Determine where best to put those sun loving plants, and finally find out just how shady is your shade garden.
Published: May 2022