Chlorosis, yellow leaves that signal nutrient deficiency in plants

Chlorosis on leaves of a bird-of-paradise plant

Chlorosis isn’t actually a disease. It is actually a physiological deficiency that plants endure when certain minerals or trace elements are found lacking in the soil. This occurs often when there is too much active lime.

An excess of limestone blocks plant roots from taking in certain elements such as iron.

Symptoms: How to recognize chlorosis?

Common symptoms

Chlorosis symptoms are very typical:

  1. Plant growth slows, mostly because photosynthesis decreases due to lack of chlorophyll.
  2. Visually, leaves turn yellow. At the beginning, only the space between leaf veins turns yellow or white, and then it slowly spreads across the entire surface.
  3. It’s a slow, progressive spread. Older leaves are impacted first. After that, younger leaves start turning yellow, too.

Specific symptoms

Secondary symptoms differ depending on the type of chlorosis.

  • Iron chlorosis: also goes by the name iron deficiency. Exact same symptoms as described above. However, in this particular case, leaf veins stay green. Only the flat portion between them loses its green color.
  • Magnesium chlorosis: after turning yellow, leaves turn brown and fall off.
  • Phosphorus deficiency: here too, leaves turn brown. Additionally, any fruit the plant bears are misshapen.
  • Nitrogen deficiency: leaves turn almost white, losing all their color. In this case, veins turn white before the rest of the leaf.

Which plants are the hardest hit?

All plants can experience chlorosis. Nonetheless, some are more vulnerable than others. This is clearly the case for plants that love acidic soil, such as Azalea, Hydrangea, Rhododendron, etc., as well as for “calcifuge” plants of which rose trees are a classic example. Soil type is important for these particularly picky plants. Whenever there is too much limestone in the soil, be sure to expect iron chlorosis.

Preventing chlorosis

If you can, it really helps to get a soil analysis done in your garden to prevent chlorosis. This will tell you if your soil contains too much limestone, or if basic trace elements are found lacking. The following elements and minerals are crucial for photosynthesis: magnesium, potassium, zinc, nitrogen, phosphorus, iron…

Many garden centers can help you test your soil. Check with the one nearest you how to go about it.

Iron chlorosis is the easiest deficiency to deal with. All you need to do is tweak your soil until the pH reaches 6.5 or lower (more acidic). In order to do so:

  • spread a thick layer of pine bark mulch. This organic material will restore soil acidity as it breaks down;
  • favor rain water to water your plants. This is especially important if you live in an area with very hard water.

Treating chlorosis

Most common case: plants in the ground

Cutout of hibiscus leaves showing signs of chlorosisWhen you’ve identified which particular deficiency you’re dealing with, several options open up:

  • In case nitrogen is lacking, spread organic manure, such as bone meal or dried blood. Early Spring is perfect.
  • For an iron deficiency, apply chelated iron (iron chelates) in March-April, just before the growing season.
  •  As a general rule, it always helps to add compost. Compost will increase levels of iron, zinc, and nitrogen in the ground.
  • An interesting option to solve the issue in the long run is to incorporate wrought iron ornaments in the garden. Let them rust a bit as time goes by to enrich the soil around them.

Special case: container growing

In this case, it’s even easier to manage. Since chlorosis is directly linked to soil quality, this disease usually simply signals that the time has come to change the potting soil for your plant.

But if you’ve repotted your plants recently, and still see no sign of them getting any better, just follow the same steps as for plants growing in the open air.

Another path to go is that of regularly applying fertilizer, preferably a fertilizer that contains high levels of trace elements.

Garden stores also sell products for adding during watering sessions. Look them up under the “anti-chlorosis product” label.

Smart tip about treating chlorosis

A famous old tip to fight against chlorosis, especially due to iron deficiency, is to bury rusty old metal items under the soil surface.


Credits for images shared to Nature & Garden (all edits by Gaspard Lorthiois):
Bird of paradise with chlorosis by Scot Nelson under Public Domain
Chlorosis on hibiscus by Scot Nelson under Public Domain