An Essential Guide to Sun Exposure for Gardeners
If you’re confused about the difference between full sun, partial sun, and shade, you’re not alone. In this article, former organic farmer Logan Hailey digs into the nuances of sun exposure and how to determine the best sunlit area for specific plants.
Nearly every plant guide, nursery label, and seed packet includes a label about sun exposure. Some plants require full sun, while others are listed as partial shade or full shade. But what do these sunlight requirements actually mean, and how do they affect your garden plan? The reality is that sunlight varies widely depending on:
- Time of day (solar angle)
- Time of year (season)
- Buildings and trees (shadows and shade)
- Latitude (distance from the equator)
Let’s dig into everything you need to know about growing specific plants in different areas of sun exposure.
The Quick Answer
The basic guidelines for plant sun exposure are based on the minimum amount of direct light a plant receives throughout the day:
- Full sun: 6-8+ hours of direct sunlight
- Partial sun: 5-6 hours of sunlight
- Partial shade: 4-5 hours of dappled sunlight
- Full shade: Less than 4 hours of direct sunlight
Some plants, like native shrubs, ferns, wildflowers, and many herbs, are flexible with their light requirements. Others, like succulents, cacti, peppers, and tomatoes, strictly require a high amount of sunlight in order to develop healthy leaves, flowers, and fruits.
What is the Best Sun Exposure for a Garden?
Generally, the best solar orientation for a garden is south-facing, with any buildings or large trees located on the northern side. The sun rises in the east, hangs over your garden all day long, and sets in the west. This provides full sun exposure for flexible plantings of vegetables, fruits, herbs, and perennials.
Of course, there are plants for every type of sun exposure, including partially shaded ornamental beds and even fully shaded areas beneath trees. The key to a successful garden is matching the plant species to the right area, but this can vary widely across different climates.
For example, a lavender plant may look pale and fail to produce fragrant flowers if grown in a shady northern garden, but it may enjoy dappled afternoon shade in a hot southern climate with intense sun.
Similarly, a tomato plant may get scorched or sunburnt in harsh direct sun in the south but savor 8+ hours of bright sun in a northern garden. The tools below will help you decipher what works best for your specific location and your desired plant species.
Understanding Solar Aspect
Solar aspect describes how the sun moves across the sky and affects the light conditions of a certain place on Earth. The best way to understand the sun’s trajectory over your garden is to observe its changes throughout the day and every season of the year.
If you haven’t had the time to do that, here are the key factors to understand how sun exposure changes throughout the season and how to strategically locate plants based on sunlight.
Time of Day
We all know that the sun rises in the east and sets in the west. The optimal orientation for a garden is south-facing because the sun will rise in an arc across the sky over the entire garden, providing full sunlight for any of the plants grown in the center. Alternatively, an east-facing garden will receive predominantly morning light and may be partially or fully shaded in the late afternoon and evening if the sun descends behind a structure.
SunCalc is the best tool for visualizing sun positions at sunrise, specified times throughout the day, and sunset. Just type in your location and move the scrubber bar to see the movement throughout the day. The thin orange curve represents the sun’s trajectory, and the yellow represents the change in the sun’s arc at different times of year. If your garden is in the center of the map’s red circle, this means the sun will sit higher above the horizon at that hour and that location.
Things get more complicated when you consider houses, buildings, trees, shrubs, and the surrounding environment; they may block the sunshine from reaching certain areas. The biggest mistake you can make with sun exposure is growing full-sun plants in an area shaded by shadows for many hours of the day.
Anything that casts a consistent shadow may lead to wimpy tomato plants, subpar pepper production, and a lack of flower blooms in many species. This can become particularly problematic if a house, structures, or large trees are located near the south end of the garden (i.e., you have a north-facing yard).
On the other hand, afternoon shade can be beneficial for plants in hot climates. If you know your home casts a shadow over a certain garden bed in the late afternoon, this could be a nice location for plants sensitive to excessive heat, such as lettuce, cucumbers, or squash.
If your yard casts many shadows, you may need to prune back or even remove certain trees or shrubs to ensure enough light reaches your garden. Otherwise, you will be constrained to only partially-shaded and full-shade plants. The same concept rings true when growing indoor houseplants. A bright south or west-facing window is only useful for houseplants if no trees or large structures are shading it from the outside.
Use the FindMyShadow tool to calculate the position and height of the sun anywhere in the world and plot the shadows cast. This is especially useful if you’re buying a house, installing a greenhouse, or building a new vegetable bed.
Changes Throughout Seasons
The sun always appears to rise the same, but the Earth’s rotation on its axis and path of revolution around the sun determines how high in the sky it appears in different regions at different parts of the year. In general, the sun is more intense and higher in the center of the sky throughout the summer, and it appears much lower in the sky during the winter.
These seasonal differences in sunlight can dramatically affect your garden’s growth. For example, a tall tree on the southeast side of your yard may not be an issue in the summer because the sun’s arc shines over it. But in the winter, when the sun is lower in the sky, UV rays may not be able to reach past the tall tree into your garden.
These changes are easy to notice when you have grown in an area for a long time. But if you are new to gardening, it can take a few years for you to fully understand the patterns of growth in your specific area. My best recommendation is to use a tool designed for solar panels. If you think about it, our gardens are a bit like solar panels because we want to maximize their absorption of solar rays. Google Earth Desktop and SunEarthTools can help you locate the sun’s position at a particular time of year.
Your location in the Northern or Southern hemisphere and distance from the equator determine how intensely sunlight will hit your garden. For example, far northern growers in the Northwest, Northeast, Canada, and Alaska may have more challenges growing winter crops in November through March because of cloud cover and the sun’s very low angle in the sky. On the flip side, this is the prime summer growing season south of the equator in areas like Australia or Peru.
The farthest northern latitudes (closest to the poles) tilt so far away from the sun in their respective winters that they experience complete darkness. While most of us don’t grow in these extreme climates, it’s helpful to remember that this hemispheric tilting throughout the season also affects how the sun hits temperate gardens.
Even if you have a greenhouse or a warm space, the lack of light will cause many plants to grow so slowly that they basically go dormant until there is enough sun again. For example, I once overwintered spinach in an unheated low tunnel in New Hampshire. Although the spinach survived the frigid temperatures, it didn’t actually grow in size at all because it had such low levels of light.
However, once we neared the Spring Equinox, the spinach grew again thanks to more available light. This happened because the Earth began to tilt closer to the sun, bringing the Northern Hemisphere into a brighter exposure.
3 Main Types of Sun Exposure
Most every plant growing guide or label includes a light exposure label of full sun, partial sun/partial shade, or full shade. The widely accepted definitions behind these labels are described below.
Plants that grow in full sun need at least six to eight hours of direct sunlight every day. This means the sunshine hits the leaves head-on for at least six hours. On cloudier days, rest assured that UV light still reaches your plants as long as they are growing in a bright, exposed location. Although light is less available on cloudy days, there is usually enough sun filtering through the clouds to fuel photosynthesis.
While some full-sun plants can grow in partial shade, they may not produce as many flowers or fruit. A lack of sunlight is a leading cause of low yields because the plant doesn’t produce enough photosynthetic energy to fuel flower and fruit production.
When full sun plants lack enough light, they may become pale or yellow, develop weak stems, or become leggy. Legginess occurs when a plant, such as a tomato seedling, elongates its stem to reach toward the sun. In the process, the stem becomes weakened and grows fewer and smaller leaves farther apart.
Full sun garden plants include:
- Black-eyed Susan
A species’ native environment is the easiest clue to whether or not a plant prefers full sun. If it is an understory forest plant like Hosta, it probably can’t handle intense hot rays. Desert plants like agave need as much sun as possible. If it is a prairie wildflower, it also likely prefers full sun. Check your seed packets and nursery plant guidelines to confirm whether a species prefers full sun.
Partial Sun to Partial Shade
Plants that enjoy partial sun or partial shade thrive in an area with four to six hours of sunlight per day. Sometimes, the term partial sun is used to describe plants on the higher end of the spectrum (closer to six hours), while the term partial shade defines plants that do best on the lower end (around four hours). But often, the terms are used interchangeably.
The time of day when shade casts over your garden is also important. The morning sun is very different from the afternoon sun. The light earlier in the day tends to be milder, while late-day sunlight is more harsh. Both situations can be used to your advantage for specific plants. Here are more details about planting in morning shade versus afternoon shade:
If the sun doesn’t directly reach your garden until around high noon, you likely have morning shade. This type of light exposure means the afternoon sun is most direct on your garden. For example, if your house sits to the east of your garden, it will likely cast a shadow that blocks the morning sun from reaching the plants. This is perfectly fine for plants that enjoy stronger sun exposure in the afternoon.
Remember that the morning sunlight tends to be cooler and less intense, while afternoon sunlight is harsher and more direct. At northern latitudes, the afternoon sunlight may be more advantageous for plants that need a lot of light to produce flowers but get scorched from a full day of light.
Here are some plants that could benefit from morning shade and afternoon sun:
- Green onion (scallion)
- Solomon’s seal
- Black-eyed Susan
- Hardy hibiscus
Conversely, some plants need afternoon shade when the sun is most intense. This is most common with cooler-weather vegetable crops like kale or lettuce, especially if you want to grow them through the summer. Afternoon shade is advantageous for any species that tends to wilt or become stressed in the intense heat of the midday sun.
Late-day shade is particularly important in hot southern climates. If a plant grows in full sun in northern climates like Michigan, it may need afternoon shade in a southern climate like Florida. Similarly, if a spinach or pea variety is adapted to cooler spring weather, it will need afternoon shade to continue producing into early summer.
Remember that the seasonality of a crop (spring versus summer versus fall) is flexible based on your climate and the amount of light you provide. Experimentation is necessary to see what works best for you and the specific plant variety. For example, a bolt-resistant hybrid basil plant may do great in full direct sun, but a heirloom open-pollinated basil may require afternoon shade in your area because its genetics naturally make it want to go to flower in intense light.
Here are some plants that enjoy afternoon shade, especially in hot climates:
- Endive and escarole (chicories)
- Sugar snap peas
Plants that grow in full shade need only four hours of sunlight or less per day. This final form of sun exposure label may seem straightforward, but it has a few caveats. Full shade does not mean total darkness. It means only dappled sunlight reaches the plant for most of the day. In a natural environment, this typically occurs under a canopy of trees.
Most low-growing forest-floor plants are “full shade” plants. Groundcover plants and mosses also do well in shade because they are accustomed to growing under the shadows of larger plants.
All plants need light to photosynthesize, which converts carbon dioxide, sunlight, and water into glucose (sugar energy) and oxygen. Plants that grow in shade simply have more chloroplasts (the place where photosynthesis takes place), allowing them to get by on less light. As a result, many shady plants also have darker green leaves with a larger surface area.
The best plants for full shade areas include:
- Some baby greens and shade-loving vegetables (most need at least partial shade)
- American ginseng
- Creeping thyme
- Native ferns
- American beautyberry
- Black cohosh
- Coral bells
- Goat’s beard
Shade gardeners should prioritize regionally native forest understory plants because they have evolved over thousands of years to endure low light conditions. Many cultivated vegetables and flowers struggle in the low light, displaying symptoms like pale or yellowing leaves, stunted growth, lack of flowers, and absence of fruit.
Solar exposure determines how much “food” a plant can produce by photosynthesis. Some plants are adapted to partially shaded and fully shaded areas, such as a forest understory. In contrast, other plants naturally grow on exposed slopes or wide-open prairies, receiving 6+ hours of sunlight per day.
Observe how the sun arcs over your garden throughout the day and throughout the season. Use an online tool like SunCalc or make your own hand-drawn map that identifies the places where shadows may appear throughout the day due to nearby buildings, trees, and slopes. Lastly, always consider where a plant originates, which will provide the greatest clues to its light preferences.