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How Much Light Do Plants Need?
Have you ever seen a plant label with vague guidelines like “plant in full sun” or “tolerates partial sun/shade?”
If you’re new to gardening (and even if you’re not), these lighting specifications can feel a little confusing at first.
Lighting is one of the most important factors in plant growth, but it’s not always clear which plants need how much sun.
Most plant nurseries break light requirements down into three categories—full sun, partial sun (or partial shade), and full shade. Full sun means a plant needs six or more hours of sunlight each day, partial sun is used to describe between four and six hours of sunlight, and full shade means less than four hours of sunlight per day.
In this blog post, we'll explore the role of light in plant development, explain the different types of light, and offer up a few tips for optimizing light in your garden.
The right lighting is important
Light is essential for photosynthesis, which is the process by which plants make their food. In a nutshell, plants convert light energy into chemical energy in the form of glucose. Without adequate light, plants will struggle to produce enough food to grow and thrive.
On the other hand, too much light can be harmful to plants. Intense sunlight can damage plant leaves, resulting in sunburn, wilting—possibly death. It’s essential to match the right plants with their preferred lighting for optimal plant health.
Factors affecting light
All plants need some amount of sunlight each day but in varying amounts depending on the species. Not all light is equal—latitude, time of day, and the type of light affect how intense light rays are and how much light plants need for photosynthesis.
Latitude
The amount of light that plants receive varies depending on your location and the time of day. Plants in northern latitudes receive less light overall than plants in southern latitudes, even though the days are longer—the sun is further from these areas and hits the earth’s surface more indirectly.
Southern latitudes have less dramatic differences between days and nights, but the sun falls more directly on the earth and is more intensely felt by plants.
Time of day
To complicate matters, the angle of the sun changes throughout the day, which can also affect the amount of light that plants receive.
Morning and evening sun are gentle and comparatively cool, but the hottest hours of the day fall between the hours of 10 a.m. and 2 p.m. when the sun is highest in the sky. While heat-loving annuals love this kind of sunlight, it can put stress on cool-weather crops like peas and brassicas, so you may want to consider adding a shade screen to protect these more heat-sensitive plants.
Types of light
The differences between different types of light are pretty straightforward: direct light comes straight from the sun, while indirect light is filtered through trees or other objects. Of course, artificial light is produced from grow lights or lamps.
Plants can use all of these types of light for photosynthesis, but plants may need different amounts of different light sources to achieve the same results.
The fun phenomenons of phototropism and photoperiodism
Phototropism occurs when plants follow the sun throughout the day, and is the reason plants tend to grow towards windows or other sources of light. Some plants (including sunflowers) move more dramatically than other plants, and that’s completely normal.
If your plants are not getting enough light, you may notice them leaning toward the light source. To avoid leggy plants with slender, flimsy stems, make sure that your plants are getting direct sunlight whenever possible.
Still, other plants are triggered into their next phase of growth by how much light they receive in a given day. Plants experience photoperiodism when day length directly correlates with stages of plant growth and maturity. Plants with photoperiod sensitivity are categorized as short-day or long-day, and plants that aren’t affected by day length are dubbed day-neutral.
Onions are a great example of plants that have photoperiod sensitivity. You may have heard of long-day, short-day, and day-neutral onion varieties. Long-day onions are usually grown in northern latitudes that get more light in the summer, while short-day onions are grown in southern latitudes that get more light in the winter. Day-neutral onions can be grown anywhere, as they don't require a specific amount of light to trigger their next phase of growth.
This is why it’s so important to research seeds and onion sets before you purchase them, to make sure that you have a variety that will be regionally adapted to your climate.
Plant light requirements
Different plants require different levels of light. Some plants need full sun, while others prefer partial sun or full shade.
Generally speaking, most fruits and vegetables grow best in full-sun locations that receive at least six hours of sunlight. If you have shadier areas of your garden that receive less than six hours of sunlight, reserve that space for leafy vegetables, herbs, and brassicas.
Full Sun
Most fruiting plants require full sunlight, or at least six hours minimum, to produce delicious fruit. Ideally, fruiting plants should receive eight or more hours for the largest harvests of the sweetest fruits.
Minimum: 8 hours
Ideal: 12–16 hours
Minimum: 6 hours
Ideal: 8–10 hours
Minimum: 6 hours
Ideal: 8–10 hours
Heat-loving annual vegetables also prefer longer days with more direct sunlight.
Minimum: 6 hours
Ideal: 8 hours
Minimum: 6 hours
Ideal: 8–10 hours
Minimum: 6 hours
Ideal: 8 hours
Minimum: 6 hours
Ideal: 8 hours
Plants that produce bulbous roots tend to need more sunlight than other plants, since the plant will need to produce more sugars to store in a carbohydrate-rich root.
Minimum: 6 hours
Ideal: 8–10 hours
Minimum: 6 hours
Ideal: 8–10 hours
Minimum: 6 hours
Ideal: 6 hours
And of course, most flowering plants prefer as much sun as they can get. More sun is equivalent to more vegetative growth, which allows the plant to produce an abundance of blooms.
Minimum: 6 hours
Ideal: 8 hours
Minimum: 6 hours
Ideal: 8 hours
Minimum: 6 hours
Ideal: 8 hours
Minimum: 6 hours
Ideal: 8 hours
Partial Sun
Partial sun is best suited for leafy vegetables and herbs, especially plants that bolt easily in warmer temperatures. Giving brassicas like broccoli and cabbage less sunlight can actually slow the bolting process, encouraging the plants to make tighter heads.
Minimum: 4 hours
Ideal: 6–8 hours
Minimum: 6 hours
Ideal: 6 hours
Minimum: 5 hours
Ideal: 6 hours
Minimum: 6 hours
Ideal: 6 hours
Believe it or not, there are some flowers that will tolerate partial shade and even prefer it to abundant sunlight and soaring summer temperatures.
Minimum: 4 hours
Ideal: 6 hours
Minimum: 4 hours
Ideal: 6 hours
Full Shade
This is the hardest category to find plants for, but you’d be surprised at which plants can thrive in full-shade locations! Ferns, moss, and mushrooms are easily the best-suited for full shade. Hostas and coleus also fall into this category, and so do impatiens.
Minimum: 2 hours
Ideal: 4 hours
Understanding your plants' light requirements can help you to provide the right amount and type of light to help them thrive. It's also important to monitor your plants for signs of too much or too little light so that you can adjust your gardening practices accordingly.
Managing light in the garden
So you understand the different types of light and how it affects different plants. But now what? Lighting isn’t something you can directly control, but it is something that you can understand and work with to set up your garden for success from the very beginning.
Start by observing where the light hits your garden at different times of the day and the season, and record those notes. If you want to be a little more precise, use a sun meter to collect light readings.
Do research on the lighting needs of specific plants and place them in your garden accordingly. If you need to, create shade by using shade cloths and shade screens for the more heat and light-sensitive plants. You can always supplement your garden with outdoor grow lights, too, if needed.
Ultimately, the amount of light that plants need depends on the type of plant, the level of light, and other factors, including latitude and time of day. By understanding the role of light in plant development and using certain tools, you can even manipulate light to meet your garden’s needs.
Shop our full collection of flower, vegetable, and herb seeds today to view all of our plants for full and partial sun. No matter how much sun you get, we have plenty of options for you to build the garden you’ve always dreamed of!