SunnypatchFull sun, part sun, part shade and full shade: how many hours each means
On a plant label, full sun means at least 6 hours of direct sun a day. Part sun and part shade both mean 3 to 6 hours, and full shade means less than 3. The hours are counted in the growing season, with the sun shining straight onto the plant.
| Label | Direct sun a day | In practice |
|---|---|---|
| Full sun | 6 hours or more | Open ground, or the sunny side of a wall or fence |
| Part sun | 3 to 6 hours | Nearer 6 hours, and happy to have them in the afternoon |
| Part shade | 3 to 6 hours | Nearer 3 hours, best in the morning, out of hot afternoon sun |
| Full shade | Under 3 hours | Bright, but with little or no direct sun: the north side of a wall |
Sources draw the lines a little differently. Some put part sun at 4 to 6 hours, and some put full shade at under 2. The Royal Horticultural Society in the UK counts the hours at midsummer.
What counts as an hour of sun
Only direct sun counts
An hour counts when sunlight falls straight onto the plant. Bright light in the shadow of a wall doesn't count, however light the spot looks. Dappled light under an open tree is usually treated as part shade.
Midday hours are worth more than early or late ones
The sun is strongest in the middle of the day. Six hours that include midday do more for a tomato than six hours made up of early morning and late evening. In a hot climate it works the other way for delicate plants: morning sun with afternoon shade is the kinder half of the day.
The season matters
Count the hours in the months the plant is growing. A spot can be in full sun in June and full shade in March, because the sun is lower in spring and every shadow is longer. A 1.8 m (6 ft) fence in London casts a midday shadow about 1 m long in June and 2.3 m long in March. The guide to fence shadow lengths has the figures for other places.
How to find out how many hours your spot gets
Watch it for a day
Pick a clear day. Once an hour from sunrise to sunset, note whether the spot is in sun or in shade, or take a photo from the same place each time. Count the sunny hours. This is often called sun mapping.
One day only tells you about that time of year. Do it again in spring, at midsummer and in early autumn to see the whole growing season.
Work it out
The sun's path on any date is known exactly, so the hours can be calculated instead of watched. Sunnypatch does this: you draw the walls and fences around the spot on a satellite map, and it shows the hours of direct sun for every day of the year at once, including the months you would otherwise have to wait for.
It counts the shade from the walls you draw, under a clear sky. It doesn't know about trees, so near a tree, watch the spot as well.
Reading the result
Compare the hours for 21 June and 20 March with the table at the top.
- Over 6 hours on both dates: full sun for the whole growing season.
- Over 6 hours in June, under 3 in March: a summer-only sunny spot. It suits summer vegetables and bedding planted out in late spring, but not early crops or spring bulbs that need sun.
- 3 to 6 hours in June: part sun or part shade. Look at whether the hours come in the morning or the afternoon.
- Under 3 hours in June: full shade.
Count the hours for your own spot
Sunnypatch is free, with no sign-up. Search for your address, draw the walls and fences, and drag the pin to the spot. It gives the hours for midsummer, the equinox and midwinter, a chart of the whole year, and a calendar showing which hours of each day are in sun.
Or open an example: the shady side of a 1.8 m fence in London