Have you ever picked up a plant at a nursery or greenhouse and noticed a label with very vague light specifications, like “full sun” or partial shade?” For the gardener who’s just getting started (and for a few of us experienced growers, too) there’s certainly some confusion around these terms.
Generally speaking, full sun means a plant needs at least six hours of direct sunlight a day. Partial sun or partial shade means that the plant requires between four and six hours of direct sunlight a day, while full shade generally means that a plant prefers less than four hours of sunlight a day.
While it seems like a simple concept, there is a science to meeting plants’ light requirements. Keep reading to learn more about how types and quantities of sunlight affect plants differently, and which plants thrive in each.
Why Proper Lighting Matters
Lighting might well be the most important factor affecting plant growth, but it’s easily the most misunderstood. Good lighting isn’t as simple as night and day – it’s an intricate and complicated element that differs daily based on the seasons, weather, and latitude.
Time Of Day
It’s no secret that the hottest hours of the day are around high noon in summertime – when the sun is closest to our piece of the earth. Only full-sun, heat-loving annuals and perennials can survive that kind of direct sunlight. Other plants will need some kind of protection from the scorching afternoon sun or they’ll develop plant sunburn!
Sunlight hours don’t have to be uninterrupted – partial-shade plants actually benefit from a midday break from the sun. Cool-season plants, especially, prefer to get their sunlight in the early morning and late evening hours when the sunlight is less intense.
Consider how the sunlight hits your garden at different times of the day when staking out planting locations for your various plants.
Relation To The Sun
Your growing zone’s relation to the sun also plays an important role in how the sun’s rays will feel to plants.
Northern gardeners have less intense sunlight and less heat, with long summer days and shorter nights. Southern growers have more evenly spaced days and nights, but they might need to protect their plants from the intense midday sun.
Research your plants’ lighting needs and use that information as a guideline, but keep a watchful eye on your plants to make sure that they’re getting adequate (but never too much) sun.
Water
The more light a plant receives, the more water it will take. Allow your plants to dry out between waterings, but if you notice wilting leaves, it’s a sure sign that you need to water more.
If you can help it, water your plants in the early morning or late evening, as direct sun can burn wet foliage. You might consider installing a drip irrigation system that will automatically irrigate your plants by transferring water to their base.
You can also mulch around your plants to help conserve water through the hottest part of the day.
Photosynthesis
You might have heard the gardening adage, If you grow it for the fruit or the root, you need full sun. If you grow it for the leaves, partial shade is all you need.
Obviously, plants need sunlight to produce food to grow and propagate themselves. We all learned about photosynthesis in grade school. Essentially, plants transfer energy from the sun into an energy source they can readily use – sugar.
Plants that produce excess sugars store these sugars in their roots – which is why the sweetest beets are grown in full sun. Leafy greens like lettuce and spinach need less sunlight, and excess heat and sunlight will actually trigger bolting, rendering the leaves inedible.
Flowering and fruit production requires larger amounts of energy than vegetative growth, so plants grown for these purposes require proper lighting for the healthiest harvest.
Photoperiodism
A natural phenomenon called photoperiodism occurs when a plant’s growth is affected by the amount of light available to it and explains why some plants won’t flower or fruit without so many hours of darkness.
Cannabis and onions are two plants whose growth is highly affected by the lengthening (and shortening) of the days, but most plants are influenced by photoperiods on a less dramatic scale.
High Mowing Organic Seeds has an excellent article on photoperiodism, and places most plants into three categories based on how they respond to daylight – long-day, short-day, and day-neutral.¹ Long day varieties are favored in the north, where summer days are long and nights are shorter than 12 hours. Short-day varieties thrive closest to the equator, where days are shorter and nights are longer than 12 hours.
Proper lighting is never so crucial as when dealing with long-day or short-day plants. Fortunately, many of the easiest vegetables fall into the day-neutral group, relying on days rather than lighting to trigger maturity.
You can learn more about day length (and how it affects plant growth) here.
4 Types Of Plant Light Needs
The table below summarizes the 4 types of plant light requirements, along with some examples of plants in each category.
| Sun Light Type | Hours Of Sun | Examples Of Plants |
|---|---|---|
| Full Sun | More than 6 | zucchini beans sunflowers zinnias tomatoes cucumbers |
| Partial Sun | 4 to 6 | cabbage broccoli |
| Partial Shade | 4 to 6 | impatiens begonias spinach Swiss chard |
| Full Shade | Less than 4 | hostas coleus |
plant light requirements, along with
some examples of plants in each category.
You can learn more about each of these 4 light categories below.
Full Sun (6+ Hours)
Many of our favorite plants fit this category – zucchini, beans, sunflowers, and zinnias. Full sun plants need at least six hours of direct sunlight each day, but many plants can tolerate more.
Classic garden vegetables like tomatoes and cucumbers need at least eight hours of light each day, and some fruiting plants, including strawberries, require even more.
Heat-loving annuals and native perennial wildflowers are best suited to full sun in the garden – these are the plants that can tolerate higher temperatures and drier conditions.
Partial Sun (4 To 6 Hours)
Also called part sun, this term is sometimes used interchangeably with partial shade, but the two have slightly different meanings. While both labels generally mean between four and six hours of sunlight, plants marked “partial sun” can err on the side of warmer temperatures and more direct sunlight.
Cool-season vegetables in the Brassica family, including cabbage and broccoli, are perfect examples of plants that thrive in sunny areas – until the hottest days of summer when they require afternoon shade.
Partial Shade (4 To 6 Hours)
Often confused with partial sun, part shade plants need between four and six hours of sunlight a day. These plants can’t tolerate direct afternoon sun, preferring midday shade and the “cooler” sunlight in the early morning and late evening.
Impatiens and begonias are two flowering plants that thrive in partial shade. Leafy greens like spinach and Swiss chard will do just fine in the cooler temperatures that partial shade provides.
Full Shade (Less Than 4 Hours)
No true plant can thrive without some amount of sunlight, so don’t place your full shade plants in an area than gets no sunlight at all. Full shade is used to describe plants that get less than four hours of sunlight a day. Plants grown in full shade are usually grown for their decorative foliage, like hostas or coleus.
PennState Extension has identified three additional types of shade, and while these classifications may not be as relevant for the vegetable garden, they are helpful for gardeners growing forest botanicals like ginseng and Solomon’s seal:
Light shade sites receive partially filtered sun, such as that found under open canopied trees […] Moderate shade occurs with mostly reflected light, such as at the floor of a hardwood forest. Heavy or dense shade is a site with no direct sunlight, such as at the base of a north-facing wall or below dense evergreen trees.²
https://extension.psu.edu/planting-in-sun-or-shade
Some plants, particularly forest botanicals like ginseng and Solomon’s seal, might call for dappled shade, which is meant to replicate sunlight filtering through tree canopies to the forest floor.
While there are four main categories of lighting scenarios that describe most plants, some plants can tolerate a range of growing conditions. If your newest addition to the garden is marked “part shade to shade” or “partial sun to full sun,” you have options.
Remember to take into consideration your regional climate and place the plant in either location! If your plant doesn’t seem to be happy with its placement, you can always transplant it to a better site.
Managing Light In The Garden
The first order of business when planning a garden is determining how much light your growing space receives on average, and where. Our yards and patios tend to look differently at different times of the year.
When the sun rises and sets at an angle during the winter months, you’ll see more shadows than in midsummer when the sun hangs high in the sky. But in summer, many deciduous trees will have leaves, shading areas that seemed to receive full sun in the winter months.
Take Notes
If you can, you’ll want to observe your space for a full growing season before you build any permanent structures like raised beds or greenhouses, so that you know exactly which places in your garden receive full and partial sunlight or full and partial shade. Be sure to write down your observations so you don’t forget.
Use A Garden Light Meter
There are some tools available to take readings in your garden, but as with any tool, there is some room for error. While some gardeners have had success with garden light readers, others have remarked that weather conditions can throw off the reading completely.
These meters range in price, so start with an inexpensive one and if you feel the tool is useful you can upgrade.
To use a garden light meter, plant the meter in the ground, level with your plants and facing the light source. Rotate the meter between a few different locations during different times of the growing season to obtain the best results.
Once you know your readings, designing next season’s garden will be easy!
Observe Plant Response
Watch your plants closely – if they aren’t growing big enough or flowering and fruiting, they may need more sunlight than what they’re currently getting. If the foliage looks discolored and is crisp to the touch, the plant might be getting too much sun – there is such a thing as plant sunburn!
According to the University of Maryland Extension, leaf scorch looks like “pale, bleached or faded areas [that] eventually become brown and brittle” and the conditions worsen with water stress.³ As soon as you notice lighting issues, make a plan to move your plants to a better location. Transplant on an overcast day, water the plants thoroughly, and they will recover within a few days.
Creating Shade
Some growers have gardens that are more partial shade than anything else, but there are plenty of gardeners in warmer regions or in urban areas that see too much sun and heat to grow shade-loving crops. With a little creativity, you can create the shade you need with inexpensive materials – or you can build your plants their own shade house!
Shade Cloths & Screens
If you have a greenhouse or a hoop house, you can use shade cloths to create a partial shade environment. Best of all, you can remove or place shade cloths as needed to meet the different needs of your crops. Even if you don’t have a greenhouse, you can use a bamboo screen and place it in the field where it will cast shade on your sun-susceptible crops.
Image from:
Wikimedia Commons
courtesy of user:
T. R. Shankar Raman: https://commons.
wikimedia.org/wiki/File:RJDRP_Nursery_
DSC0282.jpg
You can learn more about shade cloth here.
Lath Houses
If no buildings or walls are available to provide your plants some shade from the scorching afternoon sun, you might consider building a structure that accomplishes that purpose.
Lath houses look like small garden sheds, but instead of being fully enclosed the building is only partially covered with narrow slats. The unique design of a typical lath house casts about 50% shade, resulting in a partial shade environment–a growing space where even the most heat and sun-sensitive plants can thrive.
In Summary
Who hasn’t been guilty of taking light for granted? We all do, but plants don’t have the luxury of stepping outside on a sunny day or putting on sunscreen. Do the responsible thing for your garden and research your plants’ lighting needs, place them appropriately in your garden, and check back frequently to make sure that they are good and well.
I hope you found this article helpful. If so, please share it with someone who can use the information.
You can get a summary of vegetable plant care basics with this free app I made.
You can learn about shade gardens (and some good plants to include) here.
If you want to read some of my most popular posts, please check out the “Best of GreenUpSide” page here. Enjoy!
~Jonathon
Resources
¹ Photoperiodism: How Day Length Affects Plant Growth,” High Mowing Seeds, 27 Nov 2017, https://www.highmowingseeds.com/blog/photoperiodism/.
² Hubbard, Pamela, “Planting In Sun Or Shade,” PennState Extension, 8 March 2018, https://extension.psu.edu/planting-in-sun-or-shade.
³ “Sunburn Damage On Flowers,” University of Maryland Extension, 17 March 2021. https://extension.umd.edu/resource/sunburn-damage-flowers.
About the author:
When not writing content or growing flowers in her native Virginia, you can find Sarah hiking a long-distance trail deep in the woods. Follow along with Sarah’s adventures at http://sarahcolliecreative.com.
