How to Assess Sunlight in Your Garden Before You Plant

Before you fall for a plant at the nursery, it helps to know how much sunlight in your garden actually reaches the spot you have in mind. Plant tags are written in light categories, which makes light the first thing to check. A sun-lover in shade tends to grow tall, thin and shy to flower, while a shade plant in hot sun can scorch.

You do not need a meter or an app. One clear day, a sheet of paper and a pencil give you a light map you can use for years.

What the label terms mean

“Direct sun” means sunlight falling straight on the leaves, with nothing in the way. Bright light under an open sky does not count toward the hours, and neither does dappled light filtered through a tree canopy, although both are useful to shade plants.

Wording varies by source, and some draw the lines a little differently. For one set of definitions, see the glossary of gardening terms from University of Illinois Extension. Treat the numbers as ranges and read each tag, since growers describe their own plants.

How to map the light, step by step

1. Pick a clear day. Choose one in the growing season. If you garden near deciduous trees, wait until they have their leaves.
2. Sketch the area. Draw a rough outline of the house, fences, trees and the places where you might plant. It does not need to be to scale.
3. Check about once an hour. Start soon after sunrise. For each spot, note whether it is in direct sun, dappled light or shade. A simple code on the sketch works well.
4. Keep going until evening. A phone timer helps. If you miss an hour, carry on; the pattern will still be clear.
5. Add up the hours. Count the hours of direct sun for each spot, and note whether they fell mostly in the morning or the afternoon.
6. Mark the zones. Outline the areas that count as full sun, part sun or part shade, and shade. This is your light map.

Repeat in another season if you can

One day shows you one day. The sun rides high in the sky in summer and low in winter, so shadows from buildings and fences are shortest at midsummer and stretch much longer in spring and fall. A bed that is sunny at the height of summer may sit in a wall’s shadow for much of the day early in the season.

Trees change the picture even more. Ground beneath a deciduous tree can be bright before the leaves open and heavily shaded once the canopy fills in. That is why early spring flowers often do well in places that are too dark for summer bloomers.

Repeating the exercise near the start, middle and end of your growing season gives a far more reliable map. If you only do it once, do it when the plants you care about will be in active growth.

Morning sun versus afternoon sun

Hours are not all equal. Morning sun arrives while the air is still cool. Afternoon sun arrives when the day is at its hottest, so the same number of hours is harder on leaves and dries the soil faster.

This matters most in hot-summer climates, where many plants labeled for full sun appreciate some shade in the afternoon. In cool-summer and far northern climates the opposite can be true, and the same plants may need all the sun the site can offer.

In the Northern Hemisphere, east-facing spots get morning sun and west-facing spots get afternoon sun. South-facing spots receive the most light across the day and north-facing spots the least. In the Southern Hemisphere, north and south are reversed.

Walls, fences and reflected heat

Structures do more than cast shadows. A light-colored wall or a stretch of paving bounces light and heat back onto nearby plants. A bed at the foot of a sunny wall can be noticeably warmer and drier than open ground a few steps away, and roof overhangs often keep rain off the soil there.

Shade also comes in different qualities. A building or solid fence casts dense shade on one side while leaving the sky open overhead, so the spot stays fairly bright. Shade beneath a thick evergreen is darker, and tree roots compete for water as well. Note these differences on your map, because “shade” on a tag usually assumes soil that is not bone dry.

What to do with the result

Match plants to the spot instead of fighting it. If the only place for a bed gets three hours of sun, choose plants labeled for part shade and enjoy them, instead of hoping that sun-lovers will cope. If you have a choice of sites, put the bed where the light suits the flowers you most want to grow.

Your map feeds straight into the next decisions. The overview of flower gardening for beginners shows where light fits alongside soil and climate. When you are ready to lay out a bed, the guide to planning your first flower bed starts from the same site notes.

For plant ideas, the list of easy perennial flowers for beginners includes choices for both sun and shade. Check each plant’s hardiness range on the tag as well as its light needs, since a perennial has to suit your winters and summers too.