Choosing Plants: Understanding Sun Exposure
The amount of sun a plant is exposed to greatly affects its development.
Knowing how much light a plant needs to thrive seems like a relatively simple issue, but the numerous descriptions for sun exposure found on plant labels can sometimes leave your head spinning. Luckily, industry standards are bringing consistency to plant labelling; understanding a few key terms will help you in selecting the right plant for your landscape conditions.
All plants require sunlight to grow, but differ in the amount and intensity of light needed to prosper. Plant labels identify the amount of sun a plant requires as full sun, part sun, part shade or full shade as defined:
- Full sun – Plants need at least 6 hours of direct sun daily.
- Part sun – Plants thrive with between 3 and 6 hours of direct sun per day.
- Part shade – Plants require between 3 and 6 hours of sun per day, but need protection from intense mid-day sun.
- Full shade – Plants require less than 3 hours of direct sun per day.
While these terms seem rather straightforward, there is some room for confusion, for example in differentiating between part sun and part shade. We may also find other descriptors on plant labels such as half-day sun or dappled shade. Let’s take a closer look.
This category is easy to understand and describes the type of light we find in bright, sunny open areas. Many full sun plants thrive under sunny skies from dawn to dusk, but others may need a bit of a break. If a plant is labelled heat or drought tolerant and full sun, it is a good bet that plant will tolerate even the most intense summer sun day in and day out. The same is true for plants with silver or gray foliage.
But some plants simply cannot take the heat. So what is a gardener to do? Think local: full sun in the Appalachian Mountains and full sun on the Gulf Coast are very different. It is important to use label recommendations as a guide and tailor these to your local conditions. Experience will help you gain a better perspective on what sun exposure means in your backyard. If you are unsure, consult your County Extension Educator to gain the best understanding of how plants respond to your local conditions.
Part Sun and Part Shade
When it comes to sun exposure the terms part shade and part sun are the most confusing. By definition they are very similar, but there are subtle differences that have led to the use of these two terms, rather than just one. Most plants requiring either part sun or part shade do well in filtered light for most of the day or direct sun during the morning or afternoon. Keep in mind that several hours of afternoon sun are more intense and create more heat than morning sun.
Plants labelled part shade are going to be more sensitive to getting too much sun, particularly in the afternoon, and will need shade during the hottest parts of the day. Plants labelled as part sun can typically tolerate more light and need a minimum amount of direct sun to thrive. These plants may bloom poorly if given too little sun. For either group, providing direct morning sun is a good choice.
Shade plants may require anything from the indirect light found on the north side of the house to the deep shade found under evergreens. True shade plants, such as many ferns, can perish in too much sun. Filtered light, such as that found beneath a tree canopy, is a good setting for full shade plants. This type of light is referred to as dappled shade and offers many gardening opportunities.
Most full shade plants can tolerate some direct sun in the morning or evening hours, but not mid-day. Watch the landscape carefully to make sure areas you consider shady do not receive shafts of light for extended periods during the day. Get familiar with sun exposure in your landscape by checking on light conditions throughout the day and over the course of a full growing season.