Where Will Shadows Fall in My Garden? Plan Sun and Shade Like a Pro

Every gardener eventually learns the hard way that a plant labelled "full sun" will sulk in a bed that spends the afternoon in the shadow of a fence. The trouble is that shade moves. It sweeps across the garden through the day and shifts with the seasons, so the sunny corner you planted in June can be in shadow by September. Rather than guess and replant, you can predict exactly where shadows will fall at any hour on any date, using nothing more than the sun's position and a little geometry. Our sun position and shadow simulator does it visually in 3D, and this guide explains how to read it for real planting and layout decisions.

The one formula behind every shadow

A shadow's length depends on just two things: how tall the object is and how high the sun sits. The relationship is simple:

shadow length = object height ÷ tan(sun elevation)

When the sun is high, its elevation angle is large, its tangent is large, and the shadow is short. When the sun is low, the tangent is tiny and the shadow stretches out enormously. The shadow always points in the direction opposite the sun: if the sun is in the south-west, the shadow falls to the north-east. Because the sun tracks across the sky through the day, every shadow in your garden pivots like the hand of a clock, long and pointing west at sunrise, short and pointing north (in the northern hemisphere) at midday, then long again and pointing east by evening.

A full day of shade, worked out

Let's trace a 3-metre fence or small tree in a mid-latitude garden (around 40 degrees north) on the summer solstice. Drop those numbers into the simulator and step through the day:

08:00 — sun low in the east (elevation about 37 degrees). Shadow about 4.0 m, thrown to the west.
10:00 — sun climbing (about 60 degrees). Shadow shrinks to about 1.8 m, pointing west-north-west.
12:00 — sun nearly overhead (about 73 degrees). Shadow at its shortest, roughly 0.9 m, pointing north.
16:00 — sun dropping in the west (about 38 degrees). Shadow back out to about 3.9 m, now pointing east.
18:00 — low evening sun (about 15 degrees). Shadow sprawls to about 11 m, pointing east-south-east.

Notice how the shadow is barely a metre at midday but eleven metres in the evening from the very same fence. A bed just east of that fence gets full morning and midday sun but is plunged into shade every evening, which is perfect for plants that resent hot afternoon sun and fine for morning-sun lovers.

Winter is the real test

Summer shadows are short and forgiving. Winter shadows are the ones that catch people out. On the winter solstice at the same 40-degree latitude, the midday sun barely reaches 26 degrees of elevation, so that same 3-metre fence casts a midday shadow of about 6 metres to the north, roughly seven times its summer midday length. Anything you want to grow on the north side of a wall, fence, or building may sit in permanent winter shade. That is why evergreen and winter-interest plantings belong where the low winter sun can still reach them, and why the far side of a tall obstruction is the place for shade-tolerant species, a compost bin, or a shed rather than a vegetable bed.

Designing the garden around the shade

Once you can see the shadows move, planning becomes straightforward:

Put sun-hungry plants where they clear the midday and afternoon shadows. Tomatoes, peppers, roses, and most vegetables want six or more hours of direct sun; check that no fence or tree shades the spot during the middle of the day across the growing season.
Use shade deliberately. The reliably shaded strip on the north side of a structure is ideal for ferns, hostas, and leafy greens that bolt in full sun, or for a cool seating nook in high summer.
Place seating and dining areas for the time you actually use them. If you eat outside in the evening, a spot that catches the low western sun after work beats a corner that bakes at noon and chills by six.
Anticipate growth. A sapling casts a short shadow now, but model it at its mature height so you are not surprised in ten years. The simulator takes any height you enter.
Respect your neighbours' structures. A tall boundary wall or a building next door can shade a surprising depth of your garden in winter, when its low-sun shadow runs several times its height.

How to run your own garden through the tool

Set your location. Choose a city preset or type your latitude and longitude and UTC offset into the simulator.
Measure the obstruction. Enter the height of the fence, wall, tree, or building whose shade you are tracking.
Pick the worst-case date. Check the winter solstice for the longest shadows and the summer solstice for the shortest, so you know the full range across the year.
Sweep the time slider and note the shadow length and direction each hour. The 3D view shows the shadow physically stretching and rotating across the ground, with a north marker for orientation.
Map it to your beds and paths and plant accordingly.

A note on precision

The simulator uses a standard textbook model of the sun's position that is accurate to about a degree of elevation, which is more than enough for planting and layout decisions. Two honest cautions, though: near sunrise and sunset the calculated shadow length grows very quickly and becomes unreliable, so treat those enormous early and late figures as "very long" rather than exact; and the model does not know about hedges, slopes, or reflected light, which soften real shade in ways geometry cannot capture. Use it to understand the pattern of sun and shade, then trust your own eyes for the fine detail. If you are also planning the built parts of the space, our room and flooring calculator and the companion guide on how much sunlight a window gets round out the picture indoors and out.