Sunlight exposure calculator for garden beds
Hours of direct sun, which way the bed faces and what is overhead. Out comes the exposure category nurseries use on plant tags, plus plants that will actually work there.
Afternoon sun hits when the air is already hot, so it counts for more.
Dappled light counts for about half. Dense canopy, about a third.
Effective exposure: about 6 sun-hours
Full sun
6+ hours of direct sun
This bed can take the sun lovers: Mediterranean herbs, grasses, roses, most vegetables. Water and mulch are the constraint, not light.
Plants that suit full sun
- Lavender · 6h minimum, sharp drainage
- Rosemary · Shrub-sized in zone 7+
- Ornamental grasses · Best colour in full sun
- Roses · Fewer diseases with more sun
- Bougainvillea · Zone 9+, or a pot
- Succulents · Sedum and sempervivum are hardy
What the categories on a plant tag mean
Nurseries use four labels and they are defined by hours of direct, unfiltered sun in midsummer. Full sun is six hours or more. Part sun is four to six hours, usually with some of it in the afternoon. Part shade is also roughly four hours, but morning or filtered light with protection from the hot afternoon. Full shade is under two to three hours of direct sun, or bright light with no direct sun at all. Dense shade, the kind under a Norway maple or a north wall with a fence, is a fifth category most tags do not mention because almost nothing sold as an ornamental enjoys it.
The reason the labels feel vague is that the line between part sun and part shade is not about hours, it is about when. Four hours of morning sun and four hours of afternoon sun are not the same four hours. Afternoon sun in July, from about 1 pm to 5 pm, delivers more heat and more water loss than an equal stretch in the morning. A hosta takes four hours of morning light and looks fine. Give it four hours of west sun and it scorches by August.
That is why the calculator asks for aspect and not just hours. A west-facing bed gets treated as if it had an extra hour or two of sun, an east-facing bed as if it had slightly less, and a north bed with a canopy overhead gets pushed toward full shade even if you counted three hours of flecks through the leaves.
How to measure the sun a bed really gets
Nobody guesses this correctly. People overestimate sun on beds near the house and underestimate it in open lawn. Measure it once, on a clear day between late May and mid July, and write it down.
The manual way: check the bed every hour from 8 am to 6 pm and note whether it is in direct sun, dappled light or shade. Add up the direct-sun hours. Dappled light through a thin canopy counts for about half. Ten minutes of attention across one day gives you a number you can trust for years, until a tree grows or a neighbour builds.
The lazy way: take a photo of the bed from the same spot at 9 am, noon, 3 pm and 6 pm. Sun on the soil in three of the four is full sun. Sun in two is part sun or part shade depending on which two. Sun in one or none is shade. The photo method also catches the thing people forget, which is that a bed against a south wall gets baked by reflected heat even in the hours it is not in direct sun.
- Measure in summer, when trees are in full leaf. Winter sun through bare branches does not count for most plants.
- A fence or house to the south of a bed steals the low winter and shoulder-season sun first, so a bed that is full sun in July can be part shade in April.
- Reflected light off white walls, glass or paving adds heat, not hours. It pushes part shade plants past their limit without showing up in a count.
Exposure by aspect, at a glance
Aspect is the direction the bed faces, meaning the direction open sky is in, away from whatever wall, fence or hedge sits behind it. This table assumes nothing overhead and no big trees nearby; the calculator adjusts from here.
| Bed faces | Typical direct sun | Character | Usually reads as |
|---|---|---|---|
| South | 8 to 10 hours | Hot, bright, dries fast | Full sun |
| West | 5 to 7 hours | Afternoon heat, harsh in summer | Full sun to part sun |
| East | 4 to 6 hours | Gentle morning light, cool afternoons | Part sun to part shade |
| North | 0 to 3 hours | Cool, even, bright but indirect | Part shade to full shade |
What to plant in each exposure
Full sun beds are the easy ones to shop for and the hard ones to keep watered. Lavender, rosemary, ornamental grasses, roses, bougainvillea, olives and most succulents want six hours minimum and sulk with less. In part sun, hydrangeas, Japanese maples, clematis and boxwood are at their best, with enough light to flower or colour up and enough shade to keep the leaves from crisping. Part shade suits hostas, ferns, hellebores, heuchera, astilbe and the woodland bulbs. Full shade is fern and hosta country, plus a few flowering shrubs like camellia and mahonia if the shade is high and bright rather than dense.
The mistake that costs the most is planting full-sun plants in part shade because the spot looks bright. Lavender in four hours of sun lives for a couple of years, flops open, flowers weakly and rots at the base in a wet winter. The reverse mistake, shade plants in full sun, at least announces itself quickly with scorched leaves so you can move them.
If a bed sits on the borderline, plant for the shadier category. Plants tolerate more shade than their tag suggests far more gracefully than they tolerate more sun. And if you want a full-sun plant in a part-sun spot, put it at the front edge of the bed where it catches the most light and gets the least competition from anything taller.
Get a plant list for this exact light
Upload a photo of the bed and the free plant finder picks species for your light, climate and the look you want.
Try the AI plant finderFrequently asked questions
Is 5 hours of sun full sun or part sun?⌄
Part sun. Full sun starts at six hours of direct light in midsummer. Five hours of afternoon sun on a west bed behaves close to full sun for heat-lovers like lavender and grasses, while five hours of morning sun on an east bed is comfortably part sun. The calculator treats the two differently for that reason.
Does morning sun or afternoon sun count for more?⌄
Afternoon sun counts for more, roughly an extra hour's worth in summer. It arrives when the air is already hot, so leaves lose water faster and soil dries out. Plants that need full sun prefer it. Plants tagged part shade specifically want to avoid it, and are happiest with morning light and afternoon protection.
What counts as dappled shade?⌄
Light that moves and flickers through a tree canopy, so the ground gets short bursts of direct sun all day rather than a solid block. Count it as about half its clock hours. Six hours of dappled light under a birch or a honey locust reads as roughly three hours of sun, which is part shade. Under a dense maple or an evergreen it is full shade.
Can I grow vegetables in part shade?⌄
Leafy crops, yes. Lettuce, spinach, chard, kale, herbs like parsley and mint all manage on four hours and often taste better for it. Root crops like carrots and beets need five to six. Fruiting crops, meaning tomatoes, peppers, squash and beans, want the full eight and produce poorly with less. Put those in the sunniest spot you have and give the shade to salad.
Does the sun exposure change through the year?⌄
A lot. The sun is much lower in the sky in spring and fall, so anything to the south of a bed casts a far longer shadow. A bed that is full sun from May to August can be part shade in March and October. Measure in summer for perennials and shrubs, since that is when they do their growing, and accept that spring bulbs will get more light than the summer number suggests.