My Elm Bonsai Leaves Are Turning Yellow

Written by sara john
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My Elm Bonsai Leaves Are Turning Yellow
A number of problems cause leaf yellowing in an elm bonsai. (Jupiterimages/ Images)

Growers often can get a good sense of their plants' overall health by looking at their leaves; this is true with the elm bonsai, a genus that encompasses approximately 45 species. Yellowing of leaves can be an early indication of a health problem and usually requires intervention by the grower. Yellow leaves most often are indicative of a fungus or bacteria but also can be associated with watering or nutrition issues. If addressed early on, treating for pests or adjusting nutrition will return the bonsai to its healthy state.


Chlorosis is a fairly common cause of yellowing leaves throughout much of the United States. It is an abiotic illness, which means it is not caused by a living organism, like a fungi or pest. Instead, reduced chlorophyll production is to blame. Chlorophyll is the material that makes leaves green and promotes the use of sunlight for production of energy and food. When these processes are interrupted, leaf health suffers. An iron deficiency is the most common culprit, and can be corrected by mixing an iron supplement into the soil. Chlorosis most frequently presents with leaves turning yellow-green in colour. These leaves will become more yellow if treatment is not applied. If left untreated, most bonsais will begin to wilt, turn brown and die off. Once at this stage, the illness will cause growth to stop and branches will die.

Mineral Deficiency

The elm bonsai, like other trees, requires a minimum of 16 vitamins and minerals to grow properly and maintain overall health. Among the most prevalent are iron, nitrogen and magnesium, as well as traces of manganese and boron. If the tree does not receive these elements naturally in the soil, the grower must add them with supplements. Early symptoms of mineral or vitamin deficiency include leaf yellowing, which will become worse if the problem is not addressed. The shade and type of yellowing often varies depending on which mineral is lacking. Nitrogen-deficient leaves, for example, turn a blotchy yellow, while magnesium deficiency commonly presents with yellow-tipped leaves.


Aphids are a common garden pest found in almost every region of the United States. The key to treating for these pests is to start as early as possible. The longer growers hold off on treatment, the more difficult it is to get rid of them. Aphids feed primarily on young trees and quickly will damage new growth. An early indication of aphids is curling and yellowing of leaves. Treat these bugs with an insecticidal spray, focusing on the undersides of leaves. Aphids are fairly resilient, so more than one application may be necessary. To control potential outbreaks, growers can apply an insecticidal soap in the early months of summer.

Root Rot

Root rot is a serious tree illness caused by a soil-borne fungi of the phytophthora variety. Proper watering and control are essential to preventing damage and possible death of the plant. Symptoms usually begin in the bark, which will show dark brown patches and eventually become dry and cracked. If left untreated, the fungi will move up the tree until leaves yellow and drop. Root rot is most prevalent in periods of extreme rain, since the fungus thrives in moisture. Growers should work to prevent problems by cleaning up fallen leaves and branches and pruning away lower branches as needed. Apply preventive fungicide once the fungus is identified, and reapply as necessary the next spring so the infection doesn't return.

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