What Does Full Sun Mean?

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You just bought this great-looking plant.  You don’t know much about it, but it sure is pretty.  The plant label says “full sun to part shade.”  What does that mean?  Does it matter?  Should you plant it by the fence, or maybe by the patio?  How many rays does the yard catch, anyway?

Knowing the conditions you have when you build a garden can make all the difference between stunning success and abject failure.  Knowing your soil type(s), how that soil uses water, and how much light your garden receives will help you choose the “right plant for the right place.”

All plants need sunlight to grow.  Through photosynthesis, plants use solar rays, nutrients in the soil, and water to manufacture the food they need to thrive.  Different types of plants need different amounts of these three basic elements and determining how much direct light your space receives is one of the first steps in building a bountiful garden that doesn’t require a lot of fuss.

Let’s look at how plant growers and garden experts describe the types of light you might find in your yard.  Hours of brightness do not have to be consecutive – it’s the total number of sunny hours that count.  And don’t worry about cloudy days.

Full sun has a very specific definition in gardening

Full (Direct) Sun

This is an area that receives six or more hours of direct, unfiltered light per day.  In nature, a site like this would be an open meadow or a prairie.

Plants That Need It

  • The vegetable garden, and it will be really happy with 8 to 10 hours!
  • Trees and shrubs like maples and oaks, junipers and arborvitae, roses, barberry, and forsythia.
  • Perennials such as coneflowers, daylilies, peonies, yarrow, bearded iris, and coreopsis.
  • Annual flowers like zinnias, marigolds, moss roses, cosmos, and petunias.

Caring for These Plants

Except for vegetables, most plants that need strong light are usually well suited to dry conditions once they are established.  Of course, all plants appreciate supplemental water in times of intense heat and drought, even sun-lovers.

A man is planting vegetables that benefit from having full sun.

Part (or Partial) Sun

If an area receives less than six but more than 4 hours of direct light each day, that area is considered part sun.  Interpret this to mean that a plant will tolerate a few hours of shade, mainly in the morning, but needs to be in full sun the rest of the day.  These are plants that need to be grown on the west side of your home.

Plants that Need It

  • Horse Chestnut, honeylocust, and Kentucky coffee tree; and smaller understory trees such as serviceberry, redbud, and witch hazel.
  • Shrubs like yews, dogwood, and viburnums.
  • Perennials like monarda, penstemon, and anemone.
  • Annuals such as begonias, calibrachoa, caladium, and some coleus.

Caring for These Plants

Plants that are susceptible to fungal diseases may stay too wet with morning dew if they are in the shade too long.  In southern climates and during hot, droughty times, these plants would benefit from extra waterings, because they receive the more intense afternoon rays.

You’ll know these plants are in too shady a location if the plants are stretched and leggy, and flowering is reduced. The presence of fungal diseases (leaf spots, mildews, etc.) can also indicate that these plants need more light.

Begonias benefit from partial sun to grow optimally.

Part (or Partial) Shade

This spot also receives less than six but more than 4 hours of sunlight, but this area would get most of its light in the morning, when the light and heat are less intense.

 Plants that Need It

  • Japanese maples, chokeberry, clethra, fothergilla, hydrangeas, and boxwood like these conditions.
  • Perennials such as astilbe, chelone, ferns, Jacob’s ladder, and some varieties of hosta can tolerate morning light.
  • Annuals like torenia, begonias, fuschia and coleus.

Caring for These Plants

These are plants that like to take the afternoon off.  Plant them on the east side of the house, or at the eastern edge of a wooded area, or under trees that provide dappled light most of the afternoon.

If these plants wilt easily, have burned-looking or scorched leaves, or have a “crispy” appearance, you’ll know they need to be moved to a shadier location.

Ferns benefit from partial shade.

Shade

Full shade is considered any area that receives less than 4 hours of sunlight per day.  Shade can be light or dappled – receiving intermittent light through the leafy canopy of a tree – or full (heavy) – under evergreens or in the shadow of a building.

Plants that Need It

  • Yews, rhododendrons, and gray dogwood will grow in full shade.
  • Perennials such as hostas, astilbe, bleeding heart, lenten rose, heuchera and ferns.
  • Annuals like impatiens, tuberous begonias, fuschia, and coleus,

Caring for These Plants

Shade plants in general like moist, cool conditions.  Some spots – especially under thirsty trees – can be dry, so these plants may need additional waterings.

Some plants require full shade to grow properly

How to Make a Sunshine Map

Knowing the areas of sun and shade on your property can help you determine what to plant where.  Tracking apps like Sunseeker and Sunnytrack can show you the solar path on any given day of the year.  But they don’t show you obstacles that can create shade, like neighboring buildings or trees.

It’s easy to make a sunshine map.  All you need is a full day at home, paper and pencil, and a clear day.

Make a chart that lists your garden areas down one side of the paper.  Write the hours of the day in 2-hour increments across the top, starting at 6:00 AM and ending at 8:00 PM.

Start early in the morning, shortly after dawn and continue through the evening. Every 2 hours, step outside, look at your gardens and write down if they are in the sun or shade.

At the end of the day, count up the number of times you wrote “sun” for each spot.  If it’s more than 6, you know you have a full sun garden!  Between 6 and 4 hours indicates a part sun/part shade area, and less than 4 hours tells you that the spot is shady.

Some gardeners will take pictures, some might want to draw a map, and others will record the information in an Excel spreadsheet.  You do what works best for you.  It doesn’t have to be complicated or down-to-the-minute exact; plants are forgiving.

It’s great if you can do this on the first day of summer, but any time a few weeks before and after will work.  Consider charting your sunshine every few months throughout the year.

If there is no way you can be home all day, there are light meters and other tools you can buy that will do the tracking for you.  Or maybe a fellow gardener has one you can borrow.

Revisit your map every couple of years – trees and hedges grow, fences get built, the neighbors put on an addition…there are lots of factors that change your light exposure over time.

Planning the amount of sunlight around your garden will be a very important task

Putting This Knowledge to Use

When you research plants for your garden, garden books, and plant tags often use symbols representing the sun.  A white or yellow circle means full sun, a gray or black circle means shade, and a half colored circle means part shade.  Sometimes the tag will list hours of sunlight, which is more helpful than the symbols.

Mapping your light throughout the day at different times during the year (yes, even in winter!) can give you a complete picture of how light moves through your property.  You will discover:

  • The best place for a vegetable garden.
  • That area under the tree is in hot, bright light from 2:00 PM until 7:00 PM.  No wonder the hostas are struggling!
  • In July, the north side of the house isn’t as shady as you thought.
  • That frost-crack susceptible tree shouldn’t be sited where it gets winter sun on its trunk.

And that new plant you bought that wants “full sun to part shade?”  Place it where it gets a minimum of 4 hours of direct sunshine, either in the morning or the afternoon.

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About the author: Alaine has been working way too hard in horticulture since 1992, beautifying golf courses, resorts, and hotels. She is a part time landscape designer who works full time caring for a 28,000 square foot public garden. At home, she maintains her own 400 square feet plot. Alaine lives in northern Illinois - zone 5b.

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