How Much Light Do Plants Need?

By Steven A. Frowine and The National Gardening Association from Gardening Basics For Dummies

Every plant needs light to grow and flourish, but the right amount of sunlight varies. When choosing plants for your garden, look at the plant label to check its light requirements. No matter what light conditions your garden has to offer, at least something should be able to grow there.

Defining light, from dense shade to full sun

You'll often see terms like part shade, light shade or deep shade to describe a plant's light requirements. But isn't shade just shade? And how much sun does "part sun" mean? This list clears the confusion:

Deep or dense shade, full shade. Look for this on the north sides of buildings and walls or under trees with low branches and dense leaves. No direct sunlight reaches the ground.
Partial shade. Find this in areas that get direct morning sun (on the east side of buildings) or afternoon sun (on the west side of structures) but none at midday, from about 10:00 to 2:00 p.m.
Light shade, dappled shade. Look for this under trees with high branches or sparse foliage.
Part sun. Same as partial shade — except plants that like part sun also tolerate midday sun.
Full sun. These places receive direct sunlight for at least 6 hours or more each day, including some or all of the midday hours.

The warmth of the sun, even more than actual light, inspires flowers to unfurl. Sunlight from the east (morning light) is considered cooler, and western sun (afternoon light) can be scorching. Many plants prefer a site with some morning sun, even until midday, and late-afternoon shade. Other plants are able to endure even the hottest conditions. A plant's tolerance, of course, varies by region. You can place the same plant in a sunnier spot in the far North than in the South.

If you have plants growing in a spot that receives a blast of late-afternoon sun, be sure to monitor their water needs closely so they don't dry out. If you find they're struggling, you can help them by installing something to cast a shadow, such as an arbor, or by planting a tree or large shrub in just the right spot. Even companion perennials or annuals planted nearby can cast enough shade to bring needed relief.

Signs of too much, too little sun

Take a daily walk through your garden to spot-check the condition of your plants. If they're unhappy with the amount of light they're receiving, you'll soon find out by the way the plant looks.

Here are some signs that a plant is getting too much sun:

Flower petals dry out.
Leaf edges look burnt or dried.
Flower color looks faded or washed out.
The entire plant starts to weaken and droop.

And here are signs that a plant isn't getting enough light:

Growth is sparse.
Stems are lanky and spindly.
The distance between leaves, where they're attached to the stems, is especially wide.
You see fewer flower buds and, thus, fewer flowers.
The entire plant leans toward the light sources.

Some of figuring out the proper location for a plant involves trial and error — you're aware that roses like a full day of sun, but you really want that bush to go in the nook that gets afternoon shade. Give the spot a try. If the plant's unhappy, you can always move it to a more appropriate spot.