Sunlight is critical for plants because it helps them perform a vital process called photosynthesis. This is how they make their own food.
Understanding the importance of sunlight is an easy skill for green-thumbed gardeners to learn. The key is to observe how sunlight affects your garden over time and throughout the seasons.
1. Plant Growth
One of the first things beginning gardeners need to understand is that sunlight varies throughout the day and year. Sunlight reaches higher on the horizon in summer, creating shorter shadows.
The biggest mistake novice gardeners make is seeing sun and assuming an area is sunny. Understanding that morning sun is cooler and less intense than afternoon sun prevents a lot of frustration in the garden.
2. Photosynthesis
Plants use sunlight to make their own food through a process called photosynthesis. This is where the pigment chlorophyll (what makes leaves green) captures energy from the sun, carbon dioxide from the air and water from the soil to produce sugars, oxygen and other organic compounds.
As the sun moves across the sky throughout the year, it affects the quality of sunlight a garden gets. Tracking how much sun your garden receives can help you choose plants that thrive in the light conditions you have available.
3. Flower Blooming
Sunlight’s angle on your garden varies from season to season. In the summer, it is higher in the sky, creating shorter shadows.
Flowering plants blossom in order to attract pollinators, which helps them set seeds. If your flowers are drooping or turning brown, they may not be receiving enough sunlight. Site them in a sunny spot where they can receive at least six hours of direct sunlight each day.
4. Sunlight Amounts for Different Plants
Many seed packages and plant descriptions indicate the sun requirements for each variety. However, what these descriptions don’t tell you is that the amount of sun your garden receives changes throughout the day and year.
The direction of sunlight matters; morning light is softer and less intense than afternoon sun. Also, the time of day when sunlight strikes a garden can be significant.
5. Full Sun Plants
Observe your garden through the seasons to get a better idea of your light conditions. Sunlight moves around throughout the day and is usually at its most intense in June.
For most plants, full sun means six or more hours of unfiltered sunlight each day. This is the level of sunlight that most flowering annuals and perennials need to thrive. It is also the best condition for growing vegetables.
6. Partial Sun Plants
When a plant is described as needing full sun, it means six or more hours of direct sunlight daily. This does not need to be consecutive—for example, it could be four hours of morning sun and three or more in the afternoon.
Consider mapping your garden and checking the sun exposure during different times of the day throughout spring, summer, and fall. Identify any sun-blocking trees or buildings.
7. Shade Plants
Many shade-loving perennials flower in low light conditions, including astilbe, hostas, and several types of ferns. Assessing shady garden areas is important – consider mapping out your garden at different times of the day throughout the year to see how sun patterns change over time.
Look for plant tags with descriptions like “part shade” or “full sun.” Plants that need 3-6 hours of sunlight are often labeled as part sun.
8. Plant Sunlight Requirement Tags
Most trees, shrubs, flowering plants and vegetable plants (along with houseplants and seed packets) come with a tag or description stating their ideal sun exposure needs. These descriptions are usually referred to as full sun, partial sun, or shade.
Plants that require “full sun” need all the sun they can get, which typically means six or more hours of direct sunlight per day. Look for a sun icon on the tags.
9. Sun Tracking in Garden
Mapping sunlight in your garden is a great way to help you identify what areas of your property are sun or shade. This can be done manually by sketching your property to scale on graph paper or using an app that does it for you.
Grab a few sheets of tracing paper and start observing the light starting about two hours after sunrise and stopping about an hour before dusk.
10. Morning Sun vs. Afternoon Sun
Sunlight can be harsh on plants, especially if it is coming directly through the leaves. Some plants prefer cooler morning sunlight to avoid intense afternoon sun.
It is important to know how much sunlight your garden receives on a regular basis. The easiest way to do this is by checking on your garden each day throughout the year. Then you can compare this information from season to season.