Start by Listening to the Leaves

Houseplants are honest communicators. Long before a plant sulks its way to the compost bin, it will shift its leaves, change colour and stretch its stems to tell you exactly what it needs. The trick is knowing which signal means what, because too much light and too little can produce surprisingly similar-looking damage. Get this one thing right and most other problems — soggy compost, pests, stalled growth — become far easier to manage.

A useful rule of thumb: light problems tend to show up in the newest growth and the overall shape of the plant first, while watering problems usually appear in older leaves lower down. Keep that in mind as you read the signs below.

Signs Your Houseplant Is Not Getting Enough Light

When a plant is running short of light, it does something wonderfully hopeful: it reaches. It invests everything in growing taller and wider in search of a brighter spot, at the expense of strong, compact growth.

• Stretched, leggy stems. Long, pale gaps between the leaves (the internodes) and spindly, floppy growth. A plant that was once bushy is suddenly all stem.
• Small, pale new leaves. Fresh growth that emerges smaller, thinner or a washed-out green compared with the older foliage.
• Leaning towards the window. If you have to rotate the pot constantly to stop it toppling, it is hunting for more light.
• Fading variegation. Patterned and coloured leaves — creams, pinks, reds — dull down as the plant produces more chlorophyll to compensate.
• Compost that stays wet. In low light a plant uses very little water, so the soil sits damp for weeks and the roots begin to rot.
• No new growth for months, or the slow yellowing and dropping of the lowest leaves.

Don't guess: hold your hand about 30cm above the foliage at midday. A crisp, clearly defined shadow means bright light, a soft fuzzy shadow means medium light, and virtually no shadow at all means the spot is too dim for most foliage plants.

Signs Your Houseplant Is Getting Too Much Light

Too much direct sun scorches leaves much as it would burn your own skin, and it can happen in a single hot afternoon through glass.

• Scorched patches. Brown, papery or bleached areas on the leaves facing the window, often with a crisp edge. These marks are permanent; the damaged leaf will not recover.
• Washed-out, silvery colour. Leaves that look faded, greyish or almost translucent rather than green.
• Curling or folding leaves, frequently with the edges turned away from the glass, as the plant tries to reduce the leaf surface exposed to the sun.
• Compost drying out within a day or two, even in a reasonably sized pot.
• Crispy tips and faded flowers on flowering plants such as orchids and anthuriums.

Remember that south-facing and west-facing windows can be brutally bright between April and September, while the very same windows are tame and welcome in December. A spot that suits a plant perfectly in winter may need a little shade in high summer.

Bright Light, Direct Sun and Heat Are Not the Same Thing

Many indoor plants, particularly those from tropical forest floors, adore bright light but hate direct sun. A monstera or a peace lily placed a metre back from a south-facing window sits in bright, indirect light and will thrive. Press the same plant against the glass and the leaves will burn.

Heat is a separate issue entirely. A plant on a windowsill above a radiator may show scorched-looking edges even in the depths of winter, simply from hot, dry air. If the damage sits on the side nearest the radiator rather than the window, move the plant rather than the curtain.

How to Adjust the Light Without Moving House

• Move it closer to the glass. Even 30cm can make a real difference. Equally, easing a scorched plant back from the window reduces intensity quickly.
• Use a sheer curtain or a net blind to filter harsh midday sun while still letting plenty of light through.
• Rotate the pot a quarter turn each week so every side receives even light and the plant grows straight rather than lopsided.
• Clean the window and the leaves. A film of dust and grime can cut the light reaching the foliage quite dramatically.
• Reposition reflectors. A pale wall, a white shelf or a mirror nearby bounces light back onto the plant.
• Consider a grow light on a timer for dim north-facing rooms or the darkest winter weeks — twelve to fourteen hours a day is ample for most foliage plants.

Match the Plant to the Window

South-facing windows offer the most light; east-facing gives gentle morning sun; west-facing delivers strong afternoon sun; north-facing is the dimmest and best suits shade lovers such as snake plants, pothos and ZZ plants. If a plant is content — steady growth, rich colour, no brown patches — leave it exactly where it is. Plants dislike being moved almost as much as they dislike the wrong light, so change one thing at a time, then give it a fortnight to respond before you adjust anything else.