Full Sun To Shade: How To Assess Light Conditions In Your Garden

When plant tags recommend full sun, part sun, part shade, or shade—what exactly does this mean? Use these tips to better understand light recommendations and how to assess the various light conditions in your garden for better planting decisions.

While full sun is essential for many fruiting crops, there are also plenty of vegetables you can grow in varying degrees of shade as well.

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Sun & Shade: Gardening 101

Whether you are growing from seed or buying annual or perennial plants at a nursery, the seed packet or plant tag will list (or show a symbol for) full sun, part sun, part shade, or shade as one of the recommended growing conditions.

Or, it may list a range like “full sun to part shade” if the plant does well with either.

This information is important because light is fuel for plant growth (through photosynthesis). The more energy a particular plant needs, the more sun it requires.

With too much or too little sun exposure, the plant may not grow as expected.

So how do you know what light conditions you have?

Whether your growing space is a balcony, patio, rooftop, or a patch of earth, it’s most likely you have an ever-changing mixture of sun and shade depending on the season and time of day.

Fortunately, it’s these sorts of inconsistencies that plants have evolved with.

We hear “full sun” and think it must mean continous, direct sun for a set number of hours a day. But really it means providing plants with at least six hours total of direct sun a day, even if it’s broken up into shorter periods that add up to that amount (or more). In other words, it’s the cummulative amount that matters.

It’s details like this that are not explained on plant tags, but helpful to know.

To get started, let’s look at the basic types of sun and shade and how to assess what you have so you can make better planting decisions.

Contents

• Why Light Conditions Vary
• Light Definitions (Sun & Shade)
  • Full Sun
  • Part Sun or Part Shade
  • Full Shade or Shade
• Assessing Light Conditions In Your Garden
• Planting Priorities For Sun & Shade
• Resources

Why Light Conditions Vary

You have probably noticed that light conditions are different in every single garden. They vary depending on the location, season, time of day, weather, and any obstacles like trees, buildings, or fences that can block or reflect light.

The same amount of sun in Ontario, Canada may be less intense than it is at a latitude closer to the equator like Miami, Florida.

An open garden bed here in Ontario will receive much more light overall in a growing season than one with more cloud cover in Seattle or Vancouver.

Direction also matters. Morning sun on an east-facing garden is much less intense than the same amount of sun on a west-facing bed in the afternoon.

Time of year changes things too. In spring, while trees are still bare, the garden below may receive full sun. By summer, the tree canopies are filled with leaves and that same area is partly or fully shaded.

And, for those of us in towns or cities, we are also more likely to have some or all of the sun blocked by nearby houses, sheds, fences or other structures during some part of the day.

As gardeners, our job is to get familiar with the unique lighting conditions within our gardens and pay attention to how they shift and change from day to day and season by season to get an overall sense of what we can grow.

Then, along, with the right soil, nutrients, and water, we can position plants where the overall sun or shade conditions best meet each plant’s needs.

Light Definitions (Sun & Shade)

There is no official guide to sun conditions because there are so many variables depending on location, time of year, and more, but many growers share basic common definitions.

Along with your plant tag information, it’s also wise to do extra research to find out whether the recommended light or shade is deal-breaker or not.

For example:

• A watermelon is going to use a lot of energy and need a certain number of growing days to reach maturity and for the fruit to ripen on the vine. That means the more full sun it can have, the better.
• Other flowering (but non-fruiting) plants may do best with full sun but also manage fine—albeit grow a little slower and bloom a little later—with some shade.

Photosynthesis

The process where plants receive sunlight and in turn create carbohydrates to fuel their growth is called photosynthesis. This is why sunlight is essential for plants—they need this light-fueled energy to grow.

How much light each plant needs, however, can vary greatly.

Fruiting crops like tomatoes and watermelons need a lot of sun (energy) over many months to get through flowering and fruiting.

Other plants like leafy salad greens have evolved in cooler, shady conditions and have lower energy needs.

This is why any flowering or fruiting crop plants should be given priority in full sun locations—they may not reach maturity without it.

Meanwhile, in general, anything like food crops grown for stems or foliage do best out of direct sun, otherwise the plant may bolt—skipping right to seed production—in a bid for its own survival.

Other non-fruiting, flowering plants do fine in those in-between spaces with a mixture of sun and shade. While they may flower a bit faster in full sun, they just grow a bit slower and bloom a bit later with some shade.

Assessing Light Conditions In Your Garden

“Sun mapping”—a process where we assess the light conditions in our gardens—does not require mathematical precision or fancy scientific instruments.

There are sun gauges or sunlight calculators made for home gardeners but they seem expensive and impractical for what they are—if they even work.

No matter how you do it, the idea is to pay attention to the light conditions throughout the garden over a period of time to determine the sunniest and shadiest spots and everything else in between.

For those of us in the northern hemisphere, June is a good time to make a sun map since the findings will average out what you get in spring and late summer/early fall.

How To Sun Map Your Garden

There is no official way to create a sun map for your garden but here are some suggestions:

• Create a basic sketch of your garden.
• Over a period of a few days, rate the sun in different areas of the garden at set times of day.
• I use a scoring system where I rate the light giving a score between 1 and 10 where
  1=dense shade and 10=full, unobstructed sun.
• Note any weather conditions that may be affecting the light such as cloud cover.
• After collecting your data, add up the scores. Highest score should be the sunniest spot; lowest should be the shadiest. The part sun/shade areas land in between.

As said, it’s an unscientific way to get more observant about your garden—particularly a new space you may not be familiar with.

Planting Priorities For Sun & Shade

There are countless exceptions to sun recommendations, but, overall, the suggestion to save sunny spots for fruiting crops and shadier spots for non-flowering plants is helpful.

Plants Requiring Full Sun

Some plants must have as much full sun as possible to successfully grow. These are the ones to give first dibs on sunny locations. They tend to be slow growers that are up against a deadline, having to flower and fruit during the main growing season before fall.

Examples include:

• Sunflowers
• Cantaloupe
• Corn
• Cucumber
• Eggplant
• Tomato
• Peppers
• Watermelon
• Squashes and Zucchni

Herbs that like full sun include basil, chives, dill, lavender, and tarragon.

Flowering perennials and wildflowers recommended for full sun loctions can often manage fine in part sun as well. It just means they might grow a bit slower or flower a little later.

Trees and shrubs like lilacs must have full sun to flower. If you have an older lilac that is no longer flowering, it could be that nearby tree canopies—that were not there when it was planted—are now blocking the light.

Others, like hydrangea, often do best with part sun or shade—too much or too little and they may not produce flowers.

Plants Requiring or Tolerating Part or Full Shade

Non-fruiting food crops grown for their edible stems and leaves do not like or require full sun.

These are crops that can be harvested at any time and do not require pollination.

They have evolved in cool, moist growing conditions and will bolt if exposed to too much light and heat.

The exact light preferences will vary depending on the species and variety.

Some cuilinary herbs fall into this group as well.

These are a few examples:

• Broccoli*
• Brussels sprouts
• Cabbage
• Cauliflower*
• Lettuce
• Kale
• Swiss chard
• Leafy greens including argula, endive, spinach, mustard greens

*The main edible parts of broccoli and cauliflower are (botanically) flowers. While they need a fair amount of sun (energy) to produce them, the challenge is to keep them happy without causing bolting.

25 Vegetables To Grow In The Shade has more recommendations.

Getting Started With Outdoor Herb Growing (Top Questions Answered) has a light chart for many common herbs.

Resources

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