Why Are Houseplant's Leaves Turning Yellow?

The simple answer is that there is no simple answer. Houseplant leaves turning yellow can be caused by several things.

• Random leaves that are yellow or have yellow patches on the window-side of the plant are probably being sunburnt. Too much sun can bleach out your leaves to a sickly yellowish-green. An easy fix is to move it to a less sunny spot.

• Upper yellow leaves are a sign of lime intolerance or chlorosis. If your water is high in lime or calcium, collect and use rainwater on your plants instead. Also repotting in an acidic potting mix will help. Often the newest leaves on acid-loving plants such as gardenias, azaleas, jasmine, or dwarf citrus are light green with dark veins, another indicator of chlorosis. Lime keeps them from absorbing the iron needed in photosynthesis. To prevent this, water them with a chelated iron fertilizer formulated for acid-loving houseplants. It will also contain trace amounts of minerals and micro-nutrients that your plants will make good use of.

• Lower yellow leaves can have several causes:
  1. If the lower leaves are turning yellow and dropping off it can be due to natural aging and die-off of the oldest leaves. Some plants shed their leaves seasonally. Don’t fret! They will respond with new growth in the spring.
  2. Yellow lower leaves can also be a sign of overwatering. Check the pot to see if the soil is soggy. If so, you have been over-watering, a common cause of death in houseplants. Let the soil dry out before watering again. Instead of watering on a schedule, test your plants by sticking your finger into the soil to see if they really are dry before watering.
  3. Lower leaves that turn yellow, dry up, and fall off can also be a sign of under-watering. Drought stress will cause the older leaves to shrivel up and drop off. Again, check the soil to see if it is dry and compacted. If so, pay more attention to how often you are watering and try to get them a drink before they get too dry. You may need to do some repotting depending on the size of the plant in relation to the amount of soil in its container. Small plants in large pots tend to be over-watered so move them to a smaller container with less soil while large plants in small pots tend to be under-watered and will need to be moved into roomier quarters with more soil.
  4. If lower leaves are yellow and a lot of leaves on the plant are pale, light green it is a sign of insufficient nitrogen in the soil. Repotting in fresh soil may perk it up or you can start fertilizing on regular basis. Nitrogen is good for foliage plants or for flowering plants that have yellow leaves and weak growth. Go easy on the fertilizer though, and always follow the manufacturer’s recommendations. Too much fertilizer won’t cure a problem overnight. In fact overfeeding is 2nd only to overwatering as the leading cause of houseplant death. One important rule of thumb is to fertilize only during times of active growth—usually spring through fall—and not when plants are resting—usually in the winter.

Don’t expect totally yellow leaves to magically green back up again, they won’t! Time to remove them, wait, and see what the new growth looks like.

Learn more about indoor plant problems, specifically how to get rid of houseplant pests.

See the Almanac’s Houseplant Guide to see more plant care tips.