No matter how long you’ve been a gardener, you’ll have questions about plants and the light they need. Add to that, that there is no standardized system for marking the light requirements on plants. Growers and retailers do the best they can to make it easy to understand, but we thought it would be nice to give a further explanation of what some terms mean.
The left column below shows some actual plant markers illustrating that many times a plant can perform in more than one situation. A light exposure designation for a specific plant often gives a range of light conditions, not just one possibility.
The right column below explains each light requirement icon in depth.
Full Sun – a minimum of 6 hours of full direct sun a day
Full Sun means this plant needs a minimum of 6 hours of full direct sun a day. Without enough sun this plant will begin to lose vigor and the ability to bloom.
It may be evident that the plant with this marking needs to be out in the sun but how much sun? You may notice that the front of your home is sunny in the morning leading you to believe that it’s the right spot for a sun-loving plant, but if that sun only lasts until noon, then no. It’s not the right spot after all.
Many full sun plants are happy in 10, 12 or 14 hours of sun a day even during the hottest part of the afternoon. Look for the designation “heat tolerant” or “drought tolerant.”
Part Sun – between 3 and 6 hours of sun a day
This plant will need between 3 and 6 hours of sun a day. More than 6 hours and it may “burn,” less than 3 hours will affect blooming and vigor. Is there a difference between part sun and part shade? Yes! There is. A part sun plant can have full sun at any time of the day whether it’s afternoon or morning sun but should not have more than 6 hours a day.
Here’s an example of a plant that can withstand a greater range of conditions.
Full sun to Part sun. What does this mean? It means it will adjust to either condition. It may behave a bit differently, i.e., it may not grow as tall as is possible in part sun but will still be a healthy plant.
Part Shade – between 3 and 6 hours of sun a day
This plant will need between 3 and 6 hours of sun a day, just as a part sun plant will BUT there is a difference! Part shade means that this plant should be protected from hot, late afternoon sun.
Here’s another example of a plant that can withstand a greater range of conditions.
Part sun to Part shade. What does this mean? It means it will adjust to either condition. It may behave a bit differently, i.e., It may show a difference in color but will still be a healthy plant. We think of hosta and heuchera as shade plants although some can tolerate full sun depending on the variety. You’ll see this fact noted on the plant label.
Shade – less than 3 or 4 hours of sun a day
What do we mean when we say a plant likes shade? It doesn’t mean a plant will survive without any sun at all. It does mean the plant should have less than 3 or 4 hours of morning sun a day.
What to do?
After the trees have leafed out in the spring, make a diagram of the areas you are planting in. Pick a day and chart the sun and shade by the hour through that day. Do this again in July. This will give you a very good idea of what kind of sun the area gets. Below are two scenarios to give you an idea of how to think about sun and shade.
Scenario 1: You see that an area gets 3 hours of morning sun. You may be surprised if you rely on this information to put in a shade plant, that later in the day as the sun moves from behind some large trees, the area may now have a few more hours of full sun. This could be a full or part sun spot. This is why it’s important to chart an entire day.
Scenario 2: You may see that an area is in full hot sun between 11 a.m. and 1 p.m. and assume that you have a full sun location. But if that area is in shade until 11 a.m. and then dappled shade after 1 p.m., you actually have a shade to part sun situation. Remember, when considering the light exposure for plants, think in ranges.
With time gardeners learn to evaluate the sun without as much thought. Already established plants that are thriving can tell you all you need to know about what kind of light exposure there is.
Beyond the labels
It would be nice if the light that our plants receive were easily evaluated! The trees, buildings, and shrubs around us can make it tricky to pinpoint light exposure hours. Another complicating factor is the movement of the earth in relation to the sun. Because of this, morning sun is not as strong as afternoon sun. 4 hours of morning sun is much less sun than 4 hours of afternoon sun. And as the earth turns on its axis through the summer, the angle at which the sun reaches the garden will continuously change. Putting these factors together tells us that a location that is full sun in April can likely be a shady area in July. This is why shade plants can be in full sun in early spring when they are beginning active growth but not later in the season.
Dappled sun is also a term often used in gardening. This is the sun that reaches through the leaves of deciduous trees. As the leaves wave in the breeze and wind, they create a changing balance of sun and shade.
Special note about Vegetables.
Vegetables will usually be marked full sun. But they will need more than 6 hours a day. Plant them where they can get 8 to 10 hours day.