For plant-parents, growing a bonsai is the best project to take on. If you’re a beginner, a juniper bonsai is relatively low maintenance. But caring for them still has a learning curve.
Many of my friends have approached me for advice when their bonsai becomes unhealthy. One sign that a juniper bonsai is in trouble is yellowing leaves. It can signify a few different issues.
Now that I’ve spent some time troubleshooting them myself, I’d like to share the main problems I've found. In most cases, the problem is improper watering, lack of nutrients, or lack of sunlight.
But disease and pests can also cause these issues, so I’ll outline how to check and treat these too. If your bonsai is yellowing, this guide will get you back on track soon.
The Juniper Bonsai Tree
A juniper bonsai is a juniper plant that has been grown and pruned to resemble a bonsai tree. They are popular among first-time growers because they are easier to shape, forgiving, and well-suited to bonsai growing techniques.
That, unfortunately, does not mean it isn’t possible to damage the tree. It still needs the right amount of sunlight, water, and nutrients. Getting this balance wrong can result in discoloration.
If you notice leaves turning yellow, here are some causes to consider.
The Main Causes of Yellowing in Juniper Bonsai Trees
Don’t give up, though. If your bonsai tree starts to turn yellow, you can still save it! Read through below to see which diagnosis fits your bonsai tree.
Both overwatering and underwatering are problems for a juniper bonsai tree. The soil needs to be consistently moist, but not waterlogged. Allow the soil to dry a little between waterings, but never completely.
Signs of underwatering are wilting and drying leaves. These will begin to fade and lose color. If you see yellow leaves and the plant has become dry, this is likely the cause.
Improve the tree's health with regular watering and do not allow the soil to completely dry out. If the soil is soggy, you may have a planter without adequate drainage holes.
Natural materials, like clay and terracotta, make a great bonsai vessel, as they wick excess moisture away from the soil. Overwatering and improper drainage leave the roots sitting in water. This can cause discoloration and lead to fungal growth.
Lack of Nutrients
Juniper bonsai trees need a balanced N-P-K fertilizer (nitrogen, potassium, and phosphorus), especially during development. If you notice yellowing on the tree, the balance of nutrients may be incorrect.
You can use a simple soil testing kit to find out what nutrient the soil is missing. Using a balanced fertilizer, you can correct this problem and restore your tree to health.
Buy fertilizers designed for bonsai growth, labeled N-P-K, for the right nutrients. Buying cheaper fertilizers damages the tree by providing improper nutrition.
Lack of Sunlight
Juniper bonsai trees need a minimum of 6 hours of direct sunlight per day. If your juniper bonsai is not receiving direct sunlight, this may be the reason it is turning yellow.
Outdoors is usually best for juniper trees, but they are fine indoors with enough light. If you cannot find a spot in your house where the tree can receive six hours of direct sunlight, move it outside.
Effects of Pruning
One reason juniper bonsai is good for beginners is that it can tolerate more aggressive pruning. But this doesn’t mean there can be no care taken at all.
Cutting instead of “pinching back” new growth can cause the surrounding needles to die and fall off, and wounds on the tree from pruning can leave it open to infection.
“Pinching back” means physically pinching away new growth between your thumb and index finger. Cutting it away with shears will cause the nearby needles to lose color and fall away.
Prune dead branches away with a concave cutter, appropriately sized for the branch. Make sure to place a wound sealant on the branch afterward, so that you don’t leave it open to moisture and infection.
Wounded twigs and improper drainage may result in fungal disease. There are two main fungal pathogens, Phomopsis Juniperovora, and Kabatina Juniperi.
Although this is a more serious problem than those outlined above, I’m going to take you through some signs to spot and treat these blights.
Phomopsis tip blight will likely appear in spring or fall when the ground is cool and wet. You will see new plant tissue lose color and fade to yellow. It is much more common in younger plants.
Kabatina blight appears from late winter to spring and causes discoloration and the death of the newer growth ends. Blights spread quickly and must be dealt with straight away.
Stop any overhead watering immediately, as the spores spread through splashing water. Remove and destroy any infected part of the plant. Apply a fungicide with the active ingredient mancozeb or thiophanate.
For Phomopsis blight, apply in early spring every two weeks and for Kabatina do the same but during the fall. These treatments are applied before the symptoms can appear, and, with care, can save your bonsai.
Juniper trees are untroubled by most pests. However, one in particular, the spider mite, can cause trouble. These mites are invisible to the naked eye but suck the sap from the tree, causing the leaves to turn yellow and brown and fall away.
In the case of a heavy infestation, you’ll notice a fine webbing, but often their presence goes completely unknown. If you suspect your plant has spider mites, regularly blast the tree with a strong jet of water.
Use insecticides against heavy infestations.
Bonsai trees are prone to stress. If there has been a sudden change in the bonsai's environment recently, this is a possible cause.
A sudden move can change temperature or moisture conditions and cause damage to the tree. Bonsai trees react badly to sudden drops in temperature, and it can lead to discolored leaves. Keep this in mind when moving them.
Over-pruning may also cause stress. You can reduce stress on the tree by reducing the amount cut from the tree at a given time. Minor pruning is considered less than 10 percent of the tree.
Don't worry if you're having some problems growing your tree. Bonsai trees are famously difficult, so it's expected that you will run into trouble somewhere.
It’s necessary to be very observant when growing a Juniper bonsai. If you notice any bad signs, react to the problem straight away. With care, the juniper bonsai can reach over 100 years old!
If you have noticed yellow leaves, there is still hope to save the plant. Whatever the issue, I hope with this guide you've found the right path to solving it.