Room setups
The south-facing bay: a greenhouse in summer, a cave in winter
A south bay is the brightest position in most houses by a very large margin, and its character changes completely between summer and winter. Getting it right means using it for the plants that genuinely want strong light, and managing the heat and the winter light drop for everything else.
| Orientation | SDirect sun |
|---|---|
| Glazing | Bay of three 1.4 x 1.6 m windows, no overhang, no external shading |
| Average light | 20,000-60,000 lx at the glass in summer, 1,000-3,000 lx at 2 m |
| Temperature range | 18-35 C at the glass in summer, 12-21 C in winter |
| Humidity band | 30-45% |
| Species that work here | Aloe vera: the plant that rots because it is treated like a houseplant, Jade plant: the winter rest that most indoor growers skip, Hoya carnosa: why your wax plant will not flower |
| What makes this room difficult |
|
presentationWhat you are seeing
- Leaves bleaching, scorching and curling on the side facing the glass in late spring and summer, on plants that were fine in March.
- Plants that thrived in the bay from March to September then yellow, drop leaves and stop growing from November onwards.
- The mix drying out within two or three days of watering in summer, and staying wet for three weeks in winter.
aetiologyWhy it happens
- Transmission through south glass at midday in summer reaches 50,000-100,000 lx, which is two orders of magnitude more than a shade plant can use. The excess destroys photosynthetic pigments, which is the bleaching and scorching.
- In winter the same glass transmits 10,000-20,000 lx at midday, and in December the day is short. The five- to tenfold seasonal drop is more than many plants can buffer, and those without a winter rest strategy decline.
- The bay acts as a solar collector. Heat builds behind the glass during the day and cannot escape, so the temperature at the glass is much higher than the room, and it falls sharply at night. Root damage from hot pots in summer and cold pots in winter both happen here.
managementWhat to do
- Divide the bay by depth. Put sun-lovers — Aloe, Jade, Hoya, string of pearls, Strelitzia — right at the glass. Put foliage plants 1.5-2 m back, where the light is 10-20% of the glass level and manageable.
- Fit a sheer or a horticultural shade net from May to September. It cuts 40-60% of the intensity and prevents scorch on anything not adapted to full sun.
- Open the windows in the bay on sunny summer days, or fit a vent. The heat build-up is the main cause of summer losses in a bay, more than the light.
- Move the pots off the floor in winter. The floor of a bay window is the coldest point in the house on a clear night, and cold roots stop taking up water.
- Adjust watering between seasons, not just the amount but the frequency. A bay plant may need water every two days in July and every three weeks in January.
- In winter, accept that growth stops and reduce feeding to nothing from October to February. Pushing growth in December in a bay produces pale, weak leaves.
Zoning the bay by depth
The useful way to think about a south bay is as three zones rather than one position. Zone one is within 30 cm of the glass: 20,000-60,000 lx in summer, 5,000-15,000 lx in winter. Zone two is 0.5-1.5 m back: 5,000-15,000 lx in summer. Zone three is 1.5-2.5 m back: 1,000-3,000 lx all year.
Zone one is for the plants that evolved in full sun and need it: Aloe, Echeveria, Jade plant, Hoya carnosa, string of pearls, Strelitzia, and most herbs. These are the plants that will not grow anywhere else in the house.
Zone two suits the bright-indirect plants: Ficus, Monstera, Begonia, Anthurium, African violet. They want the volume of light the bay provides but not the direct beam. Zone three is the zone for the shade-tolerant species, and it is often the brightest place in the house for them.
- Zone 1, at the glass: Aloe, Echeveria, Jade, Hoya, string of pearls, Strelitzia, herbs
- Zone 2, 0.5-1.5 m back: Ficus, Monstera, Begonia, Anthurium, African violet
- Zone 3, 1.5-2.5 m back: pothos, ZZ plant, snake plant, Aglaonema
- Summer at glass: 20,000-60,000 lx
- Winter at glass: 5,000-15,000 lx
The heat problem in summer
A closed bay window on a sunny June day reaches 35-40 C at the glass while the room behind it is at 22 C. That is a genuinely hostile environment for most plants, and it damages them in two ways: by cooking the leaf tissue, and by heating the pot and the root zone to temperatures that stop root function.
The two fixes are ventilation and shading, in that order. Opening the window in the bay, or fitting a vent, removes the heat at source. Shading with a sheer or net reduces the energy entering in the first place. Doing both is what makes a bay usable through July and August.
Watch the pots, not just the leaves. A black plastic pot in direct sun in a bay can reach 40 C on the sunward side, and roots at that temperature stop taking up water. Standing the pot inside a larger decorative pot, or wrapping it, buffers the root zone by several degrees.
Winter in the bay: colder than you think
A bay window loses heat on three sides, so on a clear winter night the air at the glass can be 5-8 C below the room temperature. A plant that was comfortable in zone one in July may be sitting at 8 C in January, which stops growth and, for tropical species, causes leaf drop.
The floor of the bay is the worst place. Cold air sinks, and the floor is in contact with the external wall, so a pot on the floor of a bay window can be several degrees colder than one on a windowsill 40 cm up.
The winter strategy is to move the tropical plants out of zone one entirely and let the sun-lovers — which are mostly tolerant of cool nights — have the bay to themselves until March.
Troubleshooting
What can I put right at the glass of a south bay?
My plants scorched in the bay in June. Should I have shaded them?
How often should I water in a south bay?
CaveatLight and humidity figures are measured ranges from one specific position, not guarantees. A room's readings shift with season, glazing, nearby buildings and whether lights are on in the evening, so measure your own spot before buying a plant for it.
Published2026-10-14 ·