Yellow spots on leaves

Even, fine yellow or pale dots scattered over a leaf are feeding marks. Each dot is a cell that was emptied, so the pattern is regular and nothing wipes off.

Spider mites are the usual ones indoors. They sit on the underside, and fine webbing appears in the leaf axils once the population is established. Dry warm air over a radiator suits them.

Thrips leave similar flecking with a silvery sheen, along with tiny black dots of excrement on the underside.

Stand the plant apart from the ones around it and shower it with the spray aimed up at the undersides. Then treat the undersides with a soap solution sold for plants every few days for at least three weeks, because eggs keep hatching after the first round. Look at the same leaves each time to see whether it is working.

Round or irregular spots with a darker, watery or brown edge, often ringed by a yellow halo, are leaf spot. They grow, and new ones appear, mostly on the lower leaves first.

They take hold where leaves stay wet and the air stands still. Water splashed on foliage, misting in a closed corner, and plants packed tightly together all favor it.

Take the affected leaves off and bin them. Water the soil rather than the leaves, give the plant room where air can move, and stop misting while it settles.

A photo cannot tell a fungal spot from a bacterial one, and at home both get the same answer. What decides the outcome is whether the leaves stay dry from now on.

When a leaf yellows between the veins while the veins stay clearly green, the plant is short of what it needs to build chlorophyll.

On the youngest leaves that usually points to iron, which roots take up poorly from soil that is waterlogged or has been watered with hard water for a long time. On the oldest leaves it points to magnesium instead.

Look at the pot before reaching for fertilizer. Roots sitting in wet soil take up little regardless of what is in the mix, and a plant that has been in the same soil for years has run its supply down.

A balanced houseplant fertilizer at the label dose through the growing season covers both. Repotting into fresh mix does the same job for a plant that has not been moved in years.

A dry pale patch in the middle of a leaf facing the glass is sun damage. It starts yellow and turns papery brown, and only the leaves in the light are affected.

It shows up after a move into a brighter spot, and in early spring when the sun reaches further into the room than it did all winter.

Move the plant back from the window or hang a sheer curtain. A plant coming from a dim corner needs two or three weeks of steps before it stands at the glass.

Pale rings and blotches on soft, hairy leaves such as African violet come from cold water sitting on the leaf. Water those from below and keep the foliage dry.

A night pressed against a cold windowpane, or a delivery in winter, can leave yellow blotches that brown at the edges within days. The marked leaves do not recover and the plant does.

Marks that appear once and never spread belong to an event rather than to a condition. Note when it happened and watch what the new leaves do.

A single lower leaf yellowing all over while new growth comes at the top is the normal leaf change. Cut it off once it loosens.

Several leaves yellowing at once from the bottom up, while the soil stays dark and heavy, is about water sitting in the pot rather than about spots.

A plant that pales all over with no pattern is usually short of light or of nutrients. Moving it a yard closer to the window is the first thing to try, and it is also the easiest change to reverse.