Why Do Plants Need Sunlight?

Updated: Feb. 17, 2023

It's more show than tell with indoor and outdoor plants. Learn the signs of too little light so you can put a rescue plan into action.

Why Do Plants Need Sunlight?

Two things are crucial to plant health: water and light. Sunlight powers photosynthesis, the process plants use to synthesize food. More specifically, photosynthesis is how plants make glucose, combining carbon dioxide and water. When caring for plants, indoors or outside, it’s critical to know how much water they need as well as the proper amount of light.

Just how much sunlight a plant needs depends on the plant species.┬áPlants can’t talk, but they sure know how to communicate. It’s all visual with them, like when they’re not getting enough light. Here are the signs your plant might not be getting enough light and what you can do about it.

How to Tell If Your Plant Needs More Sun

It’s Leggy

Lack of adequate light can cause plant stems to stretch to extremes as they seek light, resulting in the plant’s version of a lanky teen. How does the plant look today compared to when you purchased it? Whether it’s a houseplant or an outdoor plant, stems that seem longer with fewer leaves are signaling they need more light.

It Leans

Is your indoor or outdoor plant growing to one side or another, instead of straight up? That’s a red flag. When a plant leans toward a light source, it’s trying to find the light it needs to survive. Eventually it may also develop fewer leaves and longer stems.

Its Leaves Are Different

Changes in size and color can signal a critical light shortage. For indoor and outdoor plants, watch for leaves getting smaller or looking pale. Another sign: That beautiful variegation in the plant’s leaves that caught your eye at the nursery is nowhere in sight. Shrubs, such as variegated dogwood, need sunlight for the green and cream-colored mottling to develop in the leaves. Solid green leaves signal a light problem.

It’s Not Flowering

Some indoor plants are forced to bloom by growers, and you can have a heck of a time getting them to re-bloom. But an outdoor blooming plant like a flowering shrub? It should be flowering each year. If a potentilla isn’t flowering, or if it’s only producing a few flowers, lack of light could be the culprit.

How to Provide More Light

Follow the Guidelines

Indoor and outdoor plants are always sold with recommendations for how much light they need. Does the plant tag suggest north, south, east or west exposure? An indoor plant requiring low light might do well by a north-facing window. A perennial that needs lots of direct sunlight will do best facing southern or western sun. If you ignore the guidelines, there’s a good chance the plant won’t grow as it should.

Move Them Closer

If your indoor plants seem to be in a room where they should get enough light, but they’re still suffering, move them closer to the source of light. No place to set them? Hang them from the ceiling with plant hangers or elevate them with plant stands. Another option: Provide artificial lighting. (The University of Missouri has some great info on artificially lighting indoor houseplants.) Full-spectrum lights are sold in a range of configurations, from the classic style of long tube lighting to contemporary lamps.

Follow the Sun

Sometimes you have to chase the sun during the day so that your plants get enough of it, whether they’re indoors or outdoors on a sometimes-shady patio. To make them easier to move, put houseplants or patio plants in baskets with handles or on wheeled platforms. Then you can easily shift them around from sunny spot to sunny spot daily. Or move them every few days to give them more exposure.

Dig It Up and Relocate

If the forsythia at the corner of your house isn’t producing the springtime burst of yellow blooms that it should, accept that it’s in the wrong location, grab a shovel and move it. Transplanting is sometimes the only way to ensure a plant gets the light it needs.