Why your plant’s leaves are turning yellow

Yellowing is a plant's way of warning you, but it gives the same warning for eight different problems. The key is where it starts and what it looks like.

Quick diagnosis

What it looks like	Most likely cause
Yellow from the bottom up, soft leaf, damp soil	Overwatering
Yellow with a dry, crispy leaf, hard soil	Underwatering
Overall pale yellow, leggy plant	Not enough light
Yellow or whitish patches on the side facing the sun	Sunburn
Yellow between veins that stay green	Iron or magnesium deficiency
Yellow with tiny dots and fine webbing	Spider mites
Only one or two lower leaves, gradually	Normal aging
Sudden, widespread yellowing	Abrupt change of location or temperature

1. Overwatering — the most common cause

Drowned roots stop absorbing, the plant paradoxically dehydrates, and the lower leaves turn yellow and go soft.

What to do: stop watering and wait until the soil is truly dry. Check that the pot has drainage and that there's no water in the saucer. If the soil smells bad, take the plant out, cut off the black, mushy roots and repot it in fresh, dry potting mix. The watering guide is in how often to water your plants.

2. Underwatering

It's easy to tell apart from the previous one: the leaf is dry and crispy, not soft, and the soil has usually pulled away from the edges of the pot.

What to do: if the soil is so dry that water runs off without soaking in, submerge the whole pot in a bucket for twenty minutes.

3. Not enough light

The plant looks pale overall, with long stems and small leaves reaching for the window. Move it somewhere brighter, but gradually: a sudden move to full sun will burn it.

4. Nutrient deficiency

If the yellow appears between the veins, which stay green, it's chlorosis: a lack of iron or magnesium. It's common in plants that have been in the same soil for more than a year. Fertilize in spring and summer, and consider refreshing the potting mix.

5. Pests

Turn the leaves over and look at the undersides. If there are tiny moving dots and extremely fine webbing, it's spider mites — they show up with dry air and heat. If there are little brown bumps stuck to the stem, it's scale. Treat them with insecticidal soap or neem oil.

6. Normal aging

If it's an old lower leaf, every now and then, and the rest of the plant looks fine: nothing's wrong. Plants replace their leaves. Remove it and move on.

What not to do

The most common reflex is to water more as soon as a yellow leaf shows up. Since the number one cause is precisely too much water, that reflex kills most of the plants that are lost. Before you water, use your finger.