| Measured Sun | Shade | Latitude | Date | Orientation | Clouds | Adjusted Hours | Category |
|---|---|---|---|---|---|---|---|
| 7.0 hrs | 15% | 24.86° | 2026-03-21 | South-facing | 20% | ~6.6 hrs | Full Sun |
| 5.0 hrs | 35% | 40.71° | 2026-10-01 | Flat / Open | 40% | ~2.9 hrs | Shade |
| 8.5 hrs | 10% | -33.87° | 2026-12-15 | North-facing | 15% | ~10.2 hrs | Intense Sun |
The calculator estimates Adjusted Sun Hours by multiplying your measured direct sun by real-world modifiers:
Adjusted Hours = Measured Hours × Shade Factor × Cloud Factor × Daylength Factor × Orientation Factor × Time Factor × Canopy Factor × Reflectivity Factor
- Shade Factor = 1 − (Shade% ÷ 100)
- Cloud Factor scales 0.40–1.00 based on typical cloud cover.
- Daylength Factor = (Estimated day length ÷ 12), clamped for stability.
- Orientation/Time/Canopy/Reflectivity use practical multipliers from common garden conditions.
- Measure direct sun hours in your planting spot on a clear day.
- Estimate shade percentage from trees, walls, or structures.
- Enter latitude and a target date for the season you care about.
- Select orientation and sun window to reflect your site layout.
- Add canopy and reflective surfaces if they apply.
- Review adjusted hours and category, then pick plants accordingly.
- Use the watering change as a starting point, then observe growth.
Microclimates can shift sunlight dramatically within a few meters. Tall fences, seasonal leaf drop, and neighboring buildings are common reasons a bed behaves differently than expected.
For vegetables and flowering annuals, aim for consistent sun windows and protect roots with mulch. For leafy greens and herbs, partial shade can reduce bolting and improve summer quality.
Re-check sun patterns each season. Small changes in pruning or trellises can add meaningful light without relocating plants.
1) Why adjusted sun hours matter
Two beds can both “get six hours,” yet perform differently. Shade edges, seasonal day length, and nearby reflective surfaces change the energy plants receive. This calculator converts observed sun into an adjusted value that better matches growth and watering demand.
2) Practical light targets for common crops
Many fruiting vegetables and flowering annuals perform best at 6–8 adjusted hours daily. Leafy greens often prefer 3–6 hours to reduce heat stress and bolting. Shade-tolerant ornamentals can thrive under 0–3 hours when humidity and soil moisture are stable.
3) Season and latitude influence day length
Day length shifts as you move away from the equator. At roughly 25° latitude, day length stays fairly moderate. At 40° latitude, day length expands in summer and contracts in winter, which changes the same spot’s effective exposure across the year.
4) Clouds, canopy, and reflection change intensity
Cloud cover often reduces direct light, but plants still receive usable diffuse light. Overhead canopy can filter sun even on clear days. Bright walls, paving, and water can bounce extra light, increasing heat load and speeding soil drying in sunny corners.
5) Using results to adjust irrigation
As adjusted hours rise, evaporation and plant demand usually increase. Use the suggested watering change as a starting point, then validate with weekly observations. Mulch and wind protection can reduce swings, while exposed beds may need more frequent, deeper watering.
1) What is the difference between measured and adjusted sun hours?
Measured hours are what you observe. Adjusted hours include shade, clouds, season, and site modifiers. This helps match plant labels to real performance, especially near trees, walls, and tall structures.
2) What adjusted hours count as full sun for most plants?
Many plant tags treat 6 or more adjusted hours as full sun. Some heat-tolerant crops handle 8+ hours. If your site is hot and windy, even 6 hours can behave like intense sun.
3) How accurate is the day length estimate?
It is an approximation based on latitude and date. It is reliable for planning and comparisons, but local terrain, coastal haze, and tall buildings can still shift actual light at ground level.
4) Should I use cloud cover from a single day?
Use a typical seasonal average when possible. One cloudy day can underestimate light. If your weather varies, run two scenarios, such as 20% and 60% clouds, then compare results.
5) Why does orientation matter in the calculator?
Beds near walls can receive more or less sun depending on direction. In the northern hemisphere, south-facing areas often receive stronger exposure. In the southern hemisphere, north-facing sites are typically brighter.
6) Can reflective surfaces harm plants?
Yes. Bright walls and paving can raise leaf temperature and increase water stress. If adjusted hours are high, add mulch, increase irrigation consistency, or provide midday shade with netting.
7) How often should I re-check a garden spot?
Re-check at least each season or after major pruning. Sun angles change across the year, and trees grow. A quick re-run helps you decide when to relocate containers or switch plant varieties.