How much sun does your balcony get?

1. Choose one spot, not the whole balcony

Draw a simple sketch and mark A where you would put the pot. Observe at the approximate height of its future leaves: the floor behind a railing may be shaded while a raised plant receives sun. To compare two positions, use A and B and keep those locations fixed throughout the record.

Note the date, locality, local time and height of the point. At a window, also record whether it is inside or outside the glass, its distance from the glass and the curtain position. A window facing the sun can still be shaded by a roof; orientation alone does not describe the light reaching a plant.

2. Separate direct rays from a bright-looking space

Look for the sunlit patch reaching your chosen point; do not look directly at the Sun. A distinct shadow of your hand on that patch can help you recognise direct rays, but a generally bright room is not enough.

The RHS distinguishes direct sunshine from diffuse sky light. A spot can look bright even when a building blocks the rays. Use these four marks on the sheet; they are practical recording categories, not plant-label classifications.

• D — Direct: the sun’s rays reach the point at that moment.
• S — Shade: an obstacle blocks the rays. Add “bright” or “dark” if it helps describe the spot.
• M — Dappled: patches of sun and shade alternate, for example beneath moving leaves. Do not automatically convert this to full hours of sun.
• ? — Undetermined: you did not observe that time, or clouds prevent you from distinguishing the shadow pattern. Note the reason.

3. Make several observations through the day

Choose a day when you can check from early daylight until daylight ends, preferably with clear skies so that shadows from buildings and trees are easier to distinguish. An hourly check provides a first map. If a shadow is about to reach or leave the point, check again sooner: every 10–15 minutes, for example. This is a practical suggestion, not guaranteed precision.

Write down the actual time of each check, the code and what casts the shadow. Do not fill in a time you did not check. Note changes in the sky. When clouds hide the sun, record that fact: it does not establish that the building shades the point. Use another sheet to continue the same day.

The sheet has space for two positions and ten observations. If you follow only one spot, leave B blank. A photo from the same position can help you remember the sketch, but one photo does not summarise the day.

4. Do not add up the boxes as hours

Invented example: you see shade at 09:00, direct sun at 10:00 and 11:00, then shade at 12:00. Two D marks do not prove two hours of sun. You do not know the entry and exit times or what happened between your checks.

In a second invented example, a continuous record shows rays arriving at 09:40 and leaving at 11:10, with no observed interruptions. That interval lasts approximately 1 hour 30 minutes. It is one interval on that day, not a daily total if morning or afternoon observations are missing.

In your summary, write down the intervals you could follow and any gaps. If you only made isolated checks, keep the list of times; it is more useful than a falsely precise total.

5. Repeat before treating the pattern as a rule

The University of Minnesota recommends observing how light changes through the day and across seasons. Keep the date: the sun’s path and tree foliage change the shadows. An October observation does not by itself predict summer conditions, and October is not the same season in every country.

Repeat on another clear day to compare the pattern, and observe again in the season when the plant will grow. Recheck if an awning, curtain or tree canopy changes. If you cannot observe that season now, write down the uncertainty instead of inventing hours.

Indoors, recording that a beam passes through glass does not measure all the available light. This record measures neither intensity nor the amount of light a plant receives over the day. Nor does it turn a spot without direct sun into a spot without light.

6. Take a useful description when choosing a plant

A note such as “point A, inside the glass, 20 cm from the window; direct sun observed in the morning; afternoon not observed; record from 23 October” says more than “bright window”. This is an example description, not a measurement made by Coru.

Compare your record with the species’ needs and local advice for your climate. Sun and shade labels depend on context; we do not use an hours threshold as a universal guarantee. Temperature, wind, water, container and soil matter too. The sheet gives you a concrete observation with which to start that comparison.

About this guide

The sheet, codes and examples are by Coru. They draw on the observation and light guidance in the listed sources.

Sources & further reading

• RHS: Shade gardening — direct sunshine, diffuse light and types of shade
• University of Minnesota Extension: Gardening in the shade — observe days and seasons
• University of Minnesota Extension: Lighting for indoor plants — windows and available light
• Michigan DNR: Make a sun map — a sketch and sun observations