Environmental Causes of Yellow Leaves on Plants: Under or Over Watering, Lack of Iron or Nitrogen, and Sunburn

Sickly, yellow foliage on your favorite plant may not be a pest or disease, but rather a problem caused by environmental factors. These abiotic (non-living or non-infectious) disorders can be caused by numerous things, including climate, nutrients, and soil.

You may look at yellowing leaves on a plant and assume that it’s not getting enough water. However, the outward symptoms of both too little and too much water can be similar.

Too much water in the soil will prevent oxygen from getting to the plant’s roots, thereby smothering them. As roots die, the foliage above ground starts to discolor and die. Overwatering also promotes fungal root diseases such as armillaria and phytophthora.

Under watering will cause leaves to wilt, fade in color to a dull shade, and drop prematurely. The new growth at the tips of the plant may wilt in the afternoon and then recover in the evening. If the plant is under prolonged stress from lack of water, new leaves will be smaller and the plant will become increasingly susceptible to insects and disease.

Mineral Deficiencies - Iron or Nitrogen

If a plant is lacking in iron, new foliage will be small and it will fade to a yellowish green, starting at the edges of the leaf and spreading inward until only the veins remain green. If the plant is lacking nitrogen, older leaves will uniformly turn yellow.

To correct iron-deficient soil, aerate the soil around the roots and spread an iron chelate evenly over the soil beneath the plant canopy or apply it to the foliage, according to the product label. If you regularly mulch with composted organic matter, you will eventually remedy the iron deficiency.

A nitrogen deficiency can be fixed quickly by applying a nitrate fertilizer but this will tend to promote more rapid, succulent growth, which attracts aphids and mites. An organic form of nitrogen, such as compost, which must decompose before being absorbed by plants, will prevent the excessive growth.

Too Much Sun - Sunburned Plants

A combination of too much light and heat and not enough moisture is causes sunburn. It shows up in the areas between the veins of the foliage, appearing as a yellow or brown area, and then the foliage begins to die in that area. Vegetation growing in compacted soil is prone to sunburn - one more reason to freshen your containers each season with new potting mixture.

To prevent sunburn, choose plants that are well-suited to the site where they’re being planted. Don’t put a shade-loving plant in bright, full sun. Containers make it easier to ensure that your plant is situated in the right conditions.