Q: What is the real difference between partial shade and partial sun? It seems I am forever transplanting plants because of the light.
A: We classify a plant’s light requirements into four categories: full sun, partial sun, partial shade, and full shade. There are several variations but most people in the plant business focus on those four groups. However, many in the horticulture business use the partial shade and partial sun interchangeably which makes it difficult for the average gardener.
In general, full sun is at least 6 hours of unobstructed direct sun which is what most of the lawn grasses grown here prefer. Less than the optimal sunlight and the grass become stressed. Partial sun and partial shade usually mean 3-6 hours of sun/shade each day, preferably morning and early afternoon sun. Full shade is bright light but little or no direct sun; what we often refer to as dappled light. Most people assume full shade means no light but plants require some form of light to produce carbohydrates (sugars) for normal plant processes such as reproduction, protection and growth.
It is often very difficult to determine exactly how much light your landscape plants are receiving – with the exception of full sun. Most of our landscape plants thrive with 3-4 hours or more of morning sun then some protection from the harsh afternoon sun. It is generally thought partial shade prefers 3 hours of the morning sun with dappled light or some protection from the afternoon sun. Usually we consider the protection starting around 2 pm and going through the five o’clock hour. Partial sun can handle up to 4 – 5 hours of sun but these plants still grow best in morning sun too but can handle some afternoon sun exposure.
Remember, the longer the sun strikes an area, the warmer the area. In fact, shaded areas can be as much as 10 – 15 degrees F. cooler. The difference in temperature matters to us as humans, it will also matter to some plants. Really, in most instances, we all experience some successes and some failures when gardening. Do not be too hard on yourself if you realize plants must be moved from one location to another because of light conditions. We have all done it. I know of no gardeners, including me, who have put all their plants in the yard and never moved them. It’s what we do!