Purchased plants often come with a small tag explaining the minimum environmental requirements for them to grow. Some of those requirements are at least partially under the gardener’s control, like how much water to provide. Other requirements are a bit tougher but not impossible to change, like soil type. But requirements like sun exposure can be very difficult if not impossible to change. Sure, you could remove a tree, as long as it’s your tree and not your neighbors. You could also plant a tree and wait a decade. But for all practical purposes, you have to work with what you’ve got.
The tag typically has a sun exposure descriptor such as Full Sun or Part Shade, to help you choose appropriate plants for your garden space, but what exactly do those terms mean?
Full Sun: These plants need more than six hours of direct sunlight.
Part Sun/Part Shade: These two terms are often used interchangeably, but sometimes have slightly different meanings. Basically, these plants need between three and six hours of direct sunlight. A plant labeled Part Sun probably has a little more sun tolerance than the one labeled Part Shade. So, the Part Shade plant is best kept out of areas with too intense sunlight (imagine the difference in light intensity between a summer afternoon and mild spring morning).
Full Shade: These plants need less than three hours of direct sunlight.
Some tags might have other descriptors such as:
Filtered Light/Light Shade/Dappled Shade: These plants will do best on the northern side of a fence or structure, in spotted shade beneath a tree or pergola, or even indoors in a sunny window.
Heat and Drought Tolerant: These plants will likely do fine under intense sun and heat exposure. However, heat tolerance, and sun tolerance are not the same thing.
So how do you tell how many hours of sunlight your garden area receives? Pick a spot and check on it every hour for an entire day (or until you hit six hours of sunlight). Record if it is sun or shade each time you check it. If you are tech savvy you could set up a camera and tripod to take a picture once an hour or once every half hour then review each picture.
Also consider the time of year. The sun doesn’t get as high above the horizon in the winter as it does in the summer. Depending on the surrounding area, you might find that what is full sun in the summer, might not be in the winter. This won’t matter a bit for spring and summer annuals, they will be long dead by the time the winter solstice rolls around, but it is something to take into consideration for a perennial garden.
Lastly, use your best judgment. Take your climate into account. A bright sunny day in coastal Oregon is going to be a much different situation than a bright sunny day in Phoenix, Arizona. More importantly, your average daily weather in coastal Oregon is a lot more likely to be overcast than in Phoenix. Knowing the sun exposure and intensity of your planned garden area will help you choose the best plant species to be successful.