We see plants broken into categories according to how much sunlight they "need," but it isn't as straightforward as that. Is six hours a hard dividing line? Is morning sun the same as afternoon sunshine? Can a tomato still grow in partial sun? Let's dive in.

Many of us make the mistake of planting in an area where we think it is sunny, only to find that those plants don't flower or fruit. Disappointed, we assume we're bad gardeners and give up. However, it might simply be an issue with properly identifying where the sun falls in your yard.

When assessing sunlight levels for a particular spot in your yard, we measure how many hours the site receives sunlight, but there's more to it than a single snapshot in time or a single day in the year. Your yard may receive more or less sun at different times of the year, depending on factors such as trees, nearby buildings, and the length of daylight as the seasons shift. 

Plants vary in the amount of sunlight they can utilize, and those that survive and thrive with less, due to biological adaptations, can actually suffer damage when excessive sunlight falls on their leaves. Those that can utilize all-day sunshine will perform poorly without it. For example, traditional hostas are classified as shade-loving plants and will thrive in the less sunny spots in your yard, like under maple trees or along the north side of a house with an overhang. Planting them in a sunny location results in sunscald or leaf scorch. Planting sweet corn in a shady location will result in small, pale, and spindly plants, with no corn ears. While they won't quite die, they won't grow well or produce a crop. 

Sunlight recommendations aren't exact; they're more guidelines than actual rules, as a famous fictional pirate would say. A crabapple tree whose tag says full sun won't fail if you plant it in a spot that only gets five hours of good light per day. It'll just be a bit slower than one in the middle of a bright, sunny yard. Like most gardening, it depends, and plants are adaptable within limits. 

Full Sun

Many flowers and most of our vegetable crops are labeled as needing full sun, which generally means more than six hours of sunlight per day. Some, like corn, will be happy with as much sun as you can give it, while others, like petunias, will happily plug along with six hours of sun or even a bit less. Afternoon sun counts for more (it's more intense) than morning sun. If your spot is only receiving five hours of sun, but it's all bright afternoon rays, it will probably support plants that need full sun just fine.

The amount of sun, six or more hours in this case, doesn't need to be in one prolonged period. Two hours of morning sun and 4-5 hours of afternoon sun are still considered a full sun location. As long as the cumulative exposure of sunshine to the leaves is greater than six hours, it's a full sun spot.

Most vegetables and annual flowers thrive in full sun. The list includes sunflowers, of course, but also zinnias, dahlias, cosmos, gaillardia, osteospermum, marigolds, tomatoes, corn, melons, pumpkins and squash, potatoes, and cucumbers. Many perennials also enjoy full sun and will bloom better, grow faster, and, in the case of fruit trees, produce a heavier crop if proper attention is paid to their sunlight needs. 

Partial Sun

If it isn't full sun or shade, then partial sun is the catchall. Typically described as an area that receives 4-6 hours of sunlight per day, partial sun (sometimes referred to as partial shade) is what many areas of a yard often fall into. Don't fret if that's what your location has. Much of my vegetable patch falls into this category (my yard is full of trees), and I grow potatoes, tomatoes, onions, pumpkins, cucumbers, and more every year. You have to work with what you've got.

Partial sun is still quite wide in terms of what can be grown, and most plants will do well. You'll see a reduction in growth and yield for the most sun-loving crops, such as corn and tomatoes, but most plants will be okay. Again, it doesn't have to be consecutive, which is pretty common with large trees nearby. A spot in my yard receives two hours of morning sunlight, then remains shaded throughout midday, and receives a couple more hours of intense late afternoon light, making it ideal for partial sun plants to thrive. 

Shade

Not all shade is equal. You may hear or read about light shade, heavy shade, dappled shade (or dappled light), or partial shade. To further complicate the issue, many publications list shaded sites as receiving less than four hours of sunlight per day. A location receiving 3-4 hours of powerful afternoon sunlight doesn't really work well for shade-loving plants. 

Imagine the dark, plantless, needle-covered ground underneath a huge old spruce tree. That's full shade, and so little light reaches the ground that nearly nothing will grow there. But most shady spots are less severe. A location receiving dappled light all day, or less than two hours of sun, preferably in the morning, counts as a shaded location. Two to four hours of sun, especially if any afternoon rays are included, is more like a partial shade location. 

Plants listed as shade-loving are often sensitive to extreme heat, such as that found in a sunny spot near the driveway or against the southern edge of a building. But they don't mind a few hours of the more gentle, early morning sun. You don't have to find a spot where the sun doesn't shine to plant a hosta, fern, or coleus. Most locations which are shaded all afternoon but receive some early morning sun are fine for shade-loving plants.

How to Accurately Assess Sunlight in Your Garden

If you have a large yard with no nearby trees or tall buildings, it is likely to receive full sun. That's straightforward. But trees, houses, and even your neighbor's garage can all intercept sunlight at different times of the day, meaning you may have to do a more thorough assessment. 

Start by looking at your grass. While many factors affect how turf grows, it tends to grow more slowly and less densely in shaded locations. That's why we have grasses specifically bred to tolerate shady areas. If your grass is of a uniform variety but grows slower or less dense near a particular tree or building, that spot is likely to be partially shaded. Bright green, lush, thick grass that you can hardly keep up with in early summer is likely receiving plenty of sun for vegetables, annual flowers, and other full-sun-loving plants.

The old-fashioned way, which still works well, is to log sun exposure (or shadows) at morning, midday, and afternoon across several months of the growing season. For example, if you are planning a spot for a new apple tree or cut flower bed (full sun) but aren't sure about a specific location, you can map it out in May, June or July, and again in August. As a deciduous tree or annual flower, the plants won't care about the sunlight in December or February. 

We need to check at several periods throughout the growing season because the sun's path through the sky, and therefore the angle of the sunshine arriving in our yards, changes throughout the year. Sunlight in the third week of June (for us in the northern hemisphere) is as near to overhead as it will be through the entire year. The sun's angle will be farther to the south before and after the summer solstice, which means trees and buildings may cast shade in May, not in June or July, but again in August or September. 

If a hand-drawn map of your yard or a spreadsheet isn't your thing, try snapping a pic with your phone of the same spot at different times of the day and different months of the year. You'll be able to go back and examine when it was sunny and shady, and draw conclusions about how many hours per day the site was sunny and for what portion of the year. Remember, a spot that is in full sun all day when we plan our gardens in winter may be partially shaded or even shaded once the leaves return to the trees in spring.

For tech lovers, there are smartphone apps that provide simulations of sun or shade at various times of the day and year. These can be especially helpful if you're gardening in a new location, and haven't been around for a few seasons to map it out. 

Remember, the amount of sunshine listed on the plant tag or seed packet isn't an exact number. A plant that is labeled to receive 6 or more hours of sun won't die if given five and a half hours. Plants are resilient, and if you avoid extremes, such as planting a full shade plant in a bright, sunny spot or vice versa, you should be alright.