Sun and Shade Mapping for Your Yard: A Practical Method

Light is the site condition that most often decides whether a plant thrives, struggles or simply survives. It is also the one people most often guess at. A bed that feels sunny at lunchtime in June may be in shadow for most of the day in April, and a corner that seems shady may get four hours of hot afternoon sun.

A sun and shade map replaces guesswork with observation. It takes a few days of attention spread across the seasons, a base plan and a pencil. This guide explains the standard light categories, how to record them, how sun angle changes through the year, and how to use the results when choosing plants.

Light categories: what "full sun" and "shade" mean

Plant tags and references use a small set of light terms. Definitions vary slightly between sources, but the common hours-of-direct-sun convention is:

A few refinements matter:

• Direct sun means unobstructed sun on the leaves, not bright sky. An area under a high, open canopy may receive dappled light all day without any full direct sun.
• Hours do not need to be continuous, but timing matters. Four hours of hot afternoon sun is a much harsher condition than four hours of morning sun, especially in hot summer climates. Many plants labelled "part shade" do well with morning sun and afternoon shade but scorch with the reverse.
• Climate shifts the categories. In the hot, high-light Southwest, many "full sun" plants appreciate some afternoon shade. In the cooler, cloudier Northeast, some "part shade" plants tolerate more sun if the soil stays moist.

Orientation: start with north

Before mapping, establish where north is on your plan. Use a phone compass (allow for magnetic declination if you need precision) or an aerial image, and draw a north arrow on the base map.

In the Northern Hemisphere:

• South-facing walls and open southern exposures receive the most sun and heat.
• North sides of buildings and fences are shaded much of the day, especially in winter.
• East exposures get gentler morning sun.
• West exposures get strong afternoon sun and heat, often the most stressful condition for plants.

How sun angle changes through the year

The sun's height in the sky at midday varies with latitude and season. At solar noon, the sun's altitude is approximately 90° minus your latitude, plus about 23.4° at the June solstice and minus about 23.4° at the December solstice. The equinoxes fall in between.

That changes shadow lengths dramatically. Shadow length at solar noon is the object's height divided by the tangent of the sun's altitude:

At 40°N, the same 2 m fence casts a noon shadow of only about 0.6 m (2 ft) in June. These are noon values; in the morning and evening, shadows are much longer in every season.

The sun also rises and sets at different points on the horizon. In summer it rises north of east and sets north of west, so the north side of a house can receive early-morning and late-evening sun in June. In winter it rises south of east and sets south of west, and the north side may get no direct sun at all.

For gardens, the growing season matters most, but spring and fall shadows decide when beds warm up, where snow lingers and how early bulbs and ephemerals perform.

Mapping sun through the day

Equipment

• A base map of the yard, ideally to scale (see our guide on how to plan a backyard landscape)
• Several printed copies or tracing paper overlays
• Coloured pencils or a simple code
• A watch or phone, and a free afternoon at least once in each season

Method

1. Pick a clear day. Overcast days make shadows hard to read.
2. Observe at regular intervals, such as every two hours from about 8 am to 6 pm (adjust for daylight saving time and your day length).
3. On a fresh overlay each time, shade the areas in shadow. Note the time.
4. Stack the overlays. Count, for each part of the yard, how many observations were in sun. Multiply by the interval to estimate direct sun hours.
5. Classify each area as full sun, part sun/part shade or shade, and note whether its sun comes in the morning or afternoon.

If you cannot observe all day, phone photos taken from the same spot at intervals work well. Some people set a phone on a window ledge to take time-lapse images.

When to map

• Late spring to midsummer gives the growing-season picture most plant labels refer to.
• Around the equinoxes (late March, late September) shows shoulder-season conditions.
• Winter shows where evergreens get light, where the ground stays frozen or icy longest, and which paths stay shaded.

If you only have time for one session, choose a day in late spring or early summer after deciduous trees have leafed out, and note that winter shadows will be considerably longer.

Trees, buildings and other shade sources

Deciduous tree canopy

Deciduous trees cast dense shade in summer but let much more light through from late fall to spring. That is why spring-flowering woodland plants such as Virginia bluebells (Mertensia virginica) do their growing before the canopy closes. Map under-tree areas both before and after leaf-out if you can.

Canopy density varies. Honeylocust (Gleditsia triacanthos) casts light, dappled shade; Norway maple (Acer platanoides, listed as invasive in several states) casts dense shade. Remember that trees grow: today's part shade can become full shade in ten years. Our guide to reading mature plant sizes helps estimate future canopy.

Evergreens

Evergreen trees and tall hedges cast shade all year, including in winter when the sun is low and their shadows are longest.

Buildings, fences and walls

Structures cast predictable shadows that change with the season. Pay particular attention to:

• The north side of the house, often shaded for much of the year
• Narrow side yards between houses, which may get only an hour or two of midday sun
• New construction on neighbouring lots, which can change light conditions

Reflected light and heat

Light-coloured walls and paving reflect light and heat onto nearby plants. A bed against a south- or west-facing wall can be significantly hotter and drier than an open bed nearby, and may extend the season for tender plants or stress heat-sensitive ones.

Recording micro-sites

Light is one part of a micro-site. While mapping, also note:

• Moisture: low spots, downspout outlets, dry soil under eaves and roof overhangs
• Wind: exposed corners and gaps between buildings
• Cold air: frost pockets at the bottom of slopes where cold air settles on still nights
• Heat: reflective paving, south walls, street-side strips
• Root competition: soil under mature trees, often dry and root-filled

Give each distinct micro-site a short label on the map, such as "A: full sun, dry, reflected heat" or "D: morning sun, moist, sheltered". These labels make plant selection much faster.

Matching plants to light

With the map done, match plants to each micro-site:

1. Use the light category as a filter, then refine by moisture, soil and exposure.
2. Prefer plants whose stated range comfortably includes your conditions, rather than plants at the edge of their tolerance.
3. Consider timing: for morning-sun beds, many part-shade plants do well; for afternoon-sun beds in hot climates, choose plants with proven heat tolerance.
4. Plan for change: if a young tree will shade the bed in five to ten years, choose plants that tolerate the coming shade, or plan to replace sun lovers later.
5. Check locally. Light tolerance varies with climate. Your local extension service or native plant society can tell you how a plant performs in your area.

Plants placed in less light than they need typically flower less, grow leggy and become more prone to disease. Plants placed in more sun than they tolerate may scorch, wilt daily or need far more water.

How OpenLandscape3D helps

In the web planner you draw your property, house and site objects and orient the plan to north. Each plant in the plant library carries a sun requirement, and the OL-SUN design check flags a mismatch between a plant's needs and the light at its location. The moisture check (OL-WATER) does the same for wet or dry conditions. Checks can be overridden with a note when you know a micro-site better than the data does. The sun and water feature page describes how these checks work. The planner does not replace on-site observation: the map you make on the ground is still the best source of light data.

Frequently asked questions

How many hours is full sun?

Full sun usually means 6 or more hours of direct sun per day during the growing season. Part sun or part shade is roughly 3 to 6 hours, and shade is less than 3 hours.

Does morning sun count the same as afternoon sun?

Not really. Hours are hours on the label, but afternoon sun is hotter and more stressful. Many part-shade plants do well with morning sun and afternoon shade but suffer with the reverse, especially in hot climates.

When is the best time of year to map sun and shade?

Late spring to midsummer, after trees leaf out, gives the growing-season picture plant labels describe. Mapping again near the equinoxes and in winter adds useful detail about longer shadows.

Can a north-facing yard grow sun-loving plants?

Often in parts of it. Areas farther from the house may still receive 6 or more hours in summer, when the sun is high. Map the yard rather than assuming the whole space is shaded.

Is dappled shade under a tree the same as full shade?

No. Dappled shade under a high, open canopy can provide plenty of light for many part-shade plants. Dense shade under low or evergreen canopies is much more limiting. Root competition under trees is often an equal challenge.