What does this sun calculator calculate?
This calculator classifies a growing spot by the hours of direct sun it receives and matches that reading against the light needs of common garden crops. It reports the exposure category, the crops suited to the light, and the crops that will struggle there.
How to measure sun
Pick a clear day close to midsummer, when shadows are shortest and the reading is most honest. Check the spot once an hour and note whether it sits in direct sun. Add up the sunny hours.
A few details change the answer:
- Start counting around mid morning. Early sun is too weak to count as full exposure.
- Measure after trees have fully leafed out. A spot that is sunny in April may sit in deep shade by June.
- One reading on one day is enough for a decision, but a weekend spent checking hourly gives a much better picture.
How the classification works
The categories follow the definitions used by university extension programs:
- Full sun: 6 or more hours of direct sun
- Part sun or part shade: 4 to 6 hours
- Shade: under 4 hours
The calculator then compares your reading with the minimum light each crop needs. Fruiting crops such as tomatoes, peppers, and squash need the most light. Leafy greens, roots, and some herbs manage with less.
Reading the result
Full sun
Six or more hours supports nearly every garden crop. Fruiting vegetables need this much light to set and ripen well, and most herbs and flowers are at their best here.
Part sun or part shade
Four to six hours still grows a real garden, but the crop list narrows to leafy greens, root crops, peas, and tolerant herbs. Fruiting crops will grow but produce noticeably less, and they ripen slower as the light drops.
Shade
Under four hours is the hardest spot in the yard. Realistic options are shade tolerant greens in the brighter end of that range, woodland ornamentals, or moving the garden entirely. A sunny container on a patio often outproduces a shaded bed.
Worked examples
A spot against a fence
A bed along a south facing fence gets sun from 9 in the morning until 3 in the afternoon, when the house shades it. Six hours counts as full sun, right at the boundary, so tomatoes will grow but the earliest fruit will ripen slowly. Greens and roots are safer choices for the shadiest end of the bed.
A spot under an open tree
A bed under a honey locust gets dappled light all day plus three hours of direct afternoon sun. The honest count is about four hours: part shade. Lettuce, spinach, kale, and parsley are comfortable there, while tomatoes will disappoint.
A narrow side yard
A side yard between two houses sees direct sun only from noon to 2. Two hours is shade. Rather than fight it, the gardener keeps that space for ferns and grows vegetables in containers on the sunny driveway.
Common measuring mistakes
Counting morning sun as full sun
Light before mid morning is too weak and too slanted to carry the same weight. Extension guidance suggests counting from about 10 in the morning onward.
Measuring in early spring
Bare deciduous trees let through light that disappears once leaves emerge. A spot measured in March can lose most of its sun by June, so measure when the canopy is full or adjust for it.
Counting bright shade as sun
An open sky overhead still counts as shade. Only direct, unfiltered light on the leaves counts toward the hours.
When this calculator may not be the right choice
The reading describes total daily hours, not when the light arrives or how intense it is. Afternoon sun is stronger than morning sun at the same hour count, and summer sun in the south delivers more energy per hour than northern light. Use the classification as a starting filter, then check the individual plant page for the crops you are considering.
Frequently asked questions
How do I measure hours of sun? Watch the spot on a clear day in the growing season and note when direct sun arrives and when shade covers it. Measuring in early spring reads high, because tree canopies have not leafed out yet.
Does morning sun count the same as afternoon? The hours count equally in the classification, but afternoon sun is stronger in practice. A spot with five hours of afternoon light grows fruiting crops better than five hours of gentle morning sun.
What can I grow in part sun? Leafy greens, many herbs, and root crops manage on 4 to 6 hours. Fruiting crops like tomatoes and peppers still produce below 6 hours but yield noticeably less, and the results flag that trade-off rather than hide it.
