Light for houseplants explained: bright indirect, low light, windows and grow lights

TUREFF• •0

Light is the food of a houseplant. Watering and feeding get the attention, but a plant in the wrong light will struggle however carefully you look after it. The tricky part is that our eyes adjust so well that a room can feel bright to us while being dim to a plant.

What the labels mean

Direct light: the sun shines straight onto the leaves, usually on a sunny windowsill. Cacti, many succulents, citrus and some flowering plants enjoy it; many tropical foliage plants scorch in strong afternoon sun.
Bright indirect light: a bright spot where the sun does not hit the leaves directly, or only gently in the early morning. Near a sunny window but out of the beam, or behind a sheer curtain. This is what most popular tropical houseplants want.
Medium light: further into a bright room, or close to a window that gets no direct sun.
Low light: several metres from a window or in a room with small or shaded windows. Some plants tolerate this, but very few thrive in it. "Low light tolerant" means a plant survives and grows slowly, not that it will grow anywhere.

A rough test: hold your hand about 30 centimetres above where a plant would sit. A crisp, sharp shadow means direct light; a soft but clear shadow means bright indirect; a faint, fuzzy shadow means low light.

Window directions

Which way a window faces makes a big difference. In the northern hemisphere:

South-facing windows get the most sun through the day: good for sun-lovers, but often too strong for leafy plants right on the sill.
East-facing windows get gentle morning sun, which suits many houseplants.
West-facing windows get hotter afternoon sun.
North-facing windows get no direct sun and steady, softer light.

In the southern hemisphere it is the other way round: north-facing windows are the sunniest and south-facing ones get no direct sun. East and west behave much the same in both. Other factors matter as much: trees, buildings opposite, balconies above, net curtains and dirty glass all cut light. Light also drops off quickly with distance, so a plant a couple of metres back from a window gets far less than one on the sill.

Seasons

In winter the sun is lower and days are shorter, so light is weaker and comes further into the room. A spot that was too strong in summer can be just right in winter, and a dim spot can become too dark. Many people move plants closer to windows for the darker months, keeping them off cold glass.

Signs a plant wants more light

Long, stretched stems with big gaps between leaves, leaning hard towards the window
Small new leaves, or variegated leaves turning plain green
No flowers on a plant that should flower
Compost staying wet for a long time, since a plant in poor light uses little water

Signs of too much

Bleached, pale or yellowing patches on leaves facing the window
Brown, crispy scorch marks
Leaves curling or drooping in the hottest part of the day

Move plants gradually when changing their light. A plant shifted from a dim corner to full sun can scorch even if it is a sun-lover.

Grow lights in general

If your home is dark, LED grow lights can make up the difference. A few general points:

Full-spectrum white LEDs look natural in a living room and work well for houseplants.
Distance matters: light weakens quickly, so follow the maker's guidance on height and move the lamp closer for sun-lovers.
Plants need darkness too. A timer that gives a consistent daily period of light, rather than leaving it on around the clock, keeps things simple.
Ordinary household bulbs help a little, but are generally much weaker for plants than a light designed for growing.

Rotate pots a quarter turn every week or two so plants grow evenly instead of leaning. Which way do your windows face, and what grows best in them? Ask about a tricky spot or share what works in the comments.