Plants have very specific requirements regarding how much sun exposure they need for optimal growth. Luckily, plants usually come labeled with their sun exposure requirements and you can find their preferences in most catalogs and gardening books. However, measuring sun exposure for plants is not an exact science. There will always be variables such as cloudy days and places where it gets to be 100 degrees in the shade, and exposure preferences are also extremely dependent on how much moisture the plants get.
However, the definitions below are the generally accepted standards for determining sun exposure in the garden.
- Full Sun: At least 6 full hours of direct sunlight. Full sun is probably the trickiest level of exposure because while many plants need full sun to set buds and flower, some cannot handle the intense heat and/or dry conditions that often come with that much sunshine. One way around this is to site these plants where they will get more morning sun, than afternoon. It's cooler in the morning and as long as the plants get at least 6 hours of direct sunlight, they should grow well.
There are also many plants that will thrive in more than 6 hours of sun, that can handle dry growing conditions, once they become established. Whatever full sun plants you choose, a thick layer of mulch will help conserve moisture in the soil and keep their roots cool.
- Partial Sun / Partial Shade: These 2 terms are often used interchangeably to mean 3 - 6 hours of sun each day, preferably in the morning and early afternoon, however there is a subtle difference:
- If a plant is listed as Partial Sun, greater emphasis is put on its receiving the minimal sun requirements. These plants need several hours of sun to set flowers and fruits, but are not as fussy as sun worshippers that need a full day of sun. You may need to experiment to find the ideal spot in your garden for plants listed as Partial Sun. Luckily there are not many of them.
- If a plant is listed as Partial Shade, the plant will need some relief from the intense late afternoon sun, either from shade provided by a nearby tree or planting it on the east side of a building.
- Dappled Sun: Dappled sunlight is similar to partial shade. It is the sun that makes its way through the branches of a deciduous tree. Woodland plants and under story trees and shrubs prefer this type of sunlight over even the limited direct exposure they would get from partial shade.
- Full Shade: Less than 3 hours of direct sunlight each day, with filtered sunlight during the rest of the day. Full shade does not mean no sun. There aren't many plants, other than mushrooms, that can survive in the dark.