Bonsai tree is losing leaves – what to do about yellow leaves

In the first step of the analysis, it should be ruled out that we are talking about a deciduous tree species. If the bonsai is a gift, it is not automatically known which variety it is. Therefore, research carefully whether the leaf loss is not due to a natural, seasonal process. The care requirements should then be examined in detail.

Excessive
watering Too frequent and copious watering usually leads to waterlogging. In the further course the roots rot, so that a bonsai can hardly or no more nutrients absorb. In addition, plant bowls without a bottom opening for water drainage inevitably cause waterlogging. The leaves suffer as they starve and fall.

measures

• Repot Bonsai in fresh, well-drained substrate
• In principle, use bonsai pots with water drainage
• Do not water or water at a reduced rate for a while

Too poor watering
Few of the plants can tolerate a longer period of drought. Such neglect of care in turn means that nutrients are not transported into the leaves. Leaf shedding is the logical consequence.

measures

• Immerse the root ball in water until no more air bubbles rise
• Alternatively, pour thoroughly
• Ideally, check the substrate daily using a thumb test

Unsuitable substrate
So-called ‘department store bonsai’ are usually sold in an inferior transport substrate . Anyone who fails to repot the plant immediately for lack of experience will be confronted with leaf fall within a short time. The earth hardens completely and offers the roots neither water nor nutrients.

measures

• Immediately repot purchased or given bonsai
• Always use species-appropriate quality soil
• Optionally a mix of Akadama, lava gravel or pumice and humus

Poor location
All common types of bonsai require a location that is as bright and warm as possible. Photosynthesis is reduced where it is too dark, so that only a few leaves are needed. The mini-tree throws off the apparently superfluous specimens without further ado. If a bonsai is exposed to cold drafts, or if it is cultivated permanently at too low temperatures, the deficiency is also expressed in the fall of leaves.measures

• Prefer bright, light-flooded locations
• Avoid cold drafts and temperatures below 15 degrees Celsius
• In summer place in a bright, not full sun location in the garden or on the balcony

Unnecessary change of location
Various common tree species, such as the popular June snow (Serissa foetida), are extremely faithful to their location. They react indignantly to sudden or repeated changes by shedding their leaves.

measures

• Move bonsai as infrequently as possible
• After the leaves have shed, water and fertilize less
• If the bonsai has its full foliage again, the normal care protocol takes effect

Causes of yellow leaves

Passionate bonsai gardeners are convinced that a bonsai communicates with them by means of yellow leaves. In this way, the little tree communicates what it does not like. In addition to the classic leaf throw, yellow leaves are therefore a typical damage pattern. Experts refer to this clinical picture as chlorosis and assign it to divergent triggers. The hobby gardener is again called upon to search for the cause.

Magnesium or iron deficiency
If yellow leaf discolorations develop on the young shoots while the veins remain green, experience has shown that there is a magnesium deficiency. If this is evident in older foliage, you can assume that there is an iron deficiency. These deficits occur especially when a bonsai is watered with calcareous tap water instead of collected rainwater. If a fertilizer with a correspondingly high calcium content is added to the calcium it contains, the absorption capacity of iron and magnesium is reduced.

measures

• Always water with decalcified tap water or rainwater
• Preferably use special bonsai fertilizers from specialist dealers
• Compensate for magnesium deficiency with an Epsom salt solution from the pharmacy

Getting used to the new location
After moving to the summer balcony or from there back into the house, the less robust tree species need a period of getting used to. The same applies if you have moved into your new home after purchasing it. If the leaves turn yellow, a bonsai signals that it is not yet completely harmonizing the new site conditions.measures

• Check the local conditions after changing location
• If necessary, place in a lighter or semi-shaded, warmer or cooler place
• Carry out the move to the field step by step

Depleted substrate
The vast majority of bonsai are supplied with additional nutrients every 2 weeks from March to September. If this fertilization rhythm is neglected, the deposit in the substrate is quickly used up. In response to the predicament, the leaves turn yellow.

measures

• Fertilize a bonsai regularly during the vegetation phase
• Organic fertilizers such as rapeseed meal, blood meal, horn meal or guano are ideal
• Alternatively, use an organic liquid fertilizer

Over- fertilization Anyone who means too well with the administration of fertilizers also conjures up chlorosis. In view of the very small volume of soil that a bonsai has in its shell, the supply of nutrients requires a high degree of sensitivity. While a deficiency is relatively easy to compensate for, treating an overdose requires more effort.

measures

• Repot the bonsai immediately in fresh substrate
• Do not fertilize during the following weeks
• Always follow the dosage instructions meticulously

Strongly rooted substrate
A central aspect in the care of a bonsai is the regular repotting in a larger bowl. An interval of two to three years is mandatory. However, this is not a firmly cemented schedule, so that the small tree sometimes reaches the limit of capacity much earlier. If a bonsai gardener does not recognize the problem in the bulging roots, he can no longer overlook the yellow leaves.

measures

• Repot the bonsai in a new bowl, the length of which is 2/3 the height of the tree
• Alternatively, shorten the root area along the edge and fill up with fresh substrate
• Always carry out pruning measures during the growth break

Sunburn
Most bonsais want to spend the warm season outdoors. The mild temperatures in connection with the natural light conditions offer an optimal climate during the growth phase. The tree can build up energy reserves from which it benefits in winter. If, on the other hand, its foliage is exposed to direct sunlight, there is a risk of sunburn, which manifests itself in yellow leaves.

measures

• Do not expose the bonsai tree to direct sunlight
• Shade especially during the noon hours
• Cut off yellow leaves, water and fertilize sufficiently

Suckling pests

If a care error can be excluded as the cause of leaf fall or yellow leaves, sucking pests are targeted in the next step of the analysis. Above all, spider mites are the usual suspects, followed by aphids and scale insects, as well as mealybugs and mealybugs.

Diagnosis of spider mites
The widespread pests spread in warm, dry weather during the summer or multiply in winter when the humidity is low, caused by dry heating air. White webs can often be seen between the leaves. Due to the suckling activity, the leaves turn yellow before they wither. Spider mites initially do their thing on the underside of the leaves, so that they are often only discovered late.

Measures against spider mites

• Shower infested bonsai with as strong a water jet as possible
• Repeatedly spray with nettle stock or horsetail broth
• Put the tree in a plastic bag for 8 to 10 days and restrict the pests’ breath

Aphid diagnosis When spring heralds the outdoor season for bonsai, the aphids appear at the same time. The wingless pests are green, brown or black and vanishingly small at 1 to 7 millimeters. Like the spider mites, they cavort at the beginning on the underside of the foliage, where they suck the life of the bonsai. In doing so, they excrete honeydew, which ants target. Thus, both types of insects give each other a conspiratorial rendezvous on the bonsai, which sooner or later leads to yellow leaves.

Measures against aphids

• Again, a sharp water shower provides a remedy in the early stages
• Repeatedly spray on the well-known soft soap solution or a milk-water mix
• Use natural predators such as ladybirds, parasitic wasps or lacewing larvae

Diagnosis of mealybugs and mealybugs
If the tiny mealybugs attack a bonsai, the infestation can be recognized by small cotton balls. It is particularly insidious that they do not spare the roots themselves, so that here at the latest the supply of nutrients and water to the foliage is hindered or completely interrupted. The yellow discoloration of the leaves thus signals an immediate need for action if the afflicted bonsai is to be saved.

Measures against mealybugs and mealybugs

• Isolate the bonsai and place it as brightly as possible
• Soak a cloth or cotton swab with lemon balm spirit and wipe off the lice
• Spray the tree daily with water and additionally every 3 days with a soft soap solution

Fungal diseases

They are called Fusarium wilt, spray stain, fire blight, Verticillium wilt, or root rot. Their origins may be different; the damage they cause on the bonsai tree is always accompanied by yellow leaves. Fungal diseases spare neither the large trees nor the mini editions in bonsai culture. The therapy takes place at a largely uniform level. In addition, the cultivation conditions of the tree should be put to the test. Experience has shown that fungal spores only gain access to a plant when it is weakened, either through a pest infestation or insufficient care.

Measures against fungal diseases

• Remove and burn any infected leaves
• Treat repeatedly with liverwort extract as a natural fungicide
• As a last resort, use a systemic preparation from a specialist retailer

Conclusion
If a bonsai tree loses its leaves, this is not only very annoying, but also a warning sign. If it can be ruled out that it is a seasonal process, a thorough investigation into the cause is inevitable. There are a number of possible causes of the problem to be investigated. First and foremost, neglects during maintenance come into consideration, such as incorrect watering, an unsuitable location or depleted substrate. The same applies to the yellow leaves on a bonsai. With the help of a detailed analysis, sooner or later it becomes clear how this damage pattern could have come about. Over-fertilization is just as possible as a lack of nutrients or a sudden change of location.