How to Measure Garden Sun Hours

Count direct sun on a bed for a clear day, hour by hour, then match crops to that number. How to measure, what counts as direct sun, and common mistakes.

Published 2026-10-15 by ThriveThyme

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How to Measure Garden Sun Hours

Full sun on a seed packet means about six or more hours of direct sun. Part shade means less. Guessing from memory often overcounts. Measure one bed on a mostly clear day, then use the Sun Hours desk to see which crops fit.

What Counts

• Direct sun: a hard shadow with a clear edge. Bright open shade under a high canopy does not count as a full sun hour.
• Morning and afternoon both count when the sun hits the bed.
• Dappled light under trees usually underperforms for fruiting vegetables even when the day feels bright.

Penn State Extension and other university guides treat site light as the first filter for vegetable success. Soil and water matter, but a tomato bed with three hours of sun will not behave like a six-hour bed.

Simple Hourly Check

1. Pick a clear or mostly clear day near the season you care about. Winter sun sits lower than June sun.
2. From sunrise to sunset, note each hour when the bed gets direct sun for most of that hour.
3. Add the hours. That total is your bed number for the Sun Hours tool.
4. Recheck after trees leaf out in spring if you measured in early spring.

You can also photograph the bed each hour and tally later. A cheap sun calculator or phone app helps, but a notebook and clock work.

Common Mistakes

• Counting bright shade as full sun.
• Measuring only at noon and assuming the whole day matches.
• Ignoring a neighbor fence, garage, or new tree that cuts afternoon light.
• Using one number for every bed. Front and side yards often differ by two or more hours.

Next Steps

• Run your number through Sun Hours.
• Read vegetables that grow in part shade if you land under six hours.
• Read full sun crops and what six hours means if you have a hot, open site.