It’s an emotional blow to lose a bonsai. Even bonsai professionals and seasoned growers who know a lot about bonsai care sometimes face the unfortunate decline, and even death, of a tree. Our advice is to use tree death as an opportunity to analyze the cause so you can learn and not repeat the conditions that lead to your tree's untimely demise.
While it’s possible that you can go on vacation and come home to a dead tree because your neighbor forgot to water it, it’s also possible that your tree can die after a series of decisions to either do something or do nothing in an attempt to help the tree.
There are numerous factors that can lead to the death of a tree - watering, fertilizer, pest control, and sun protection and cold protection are among the things that if not executed properly will lead to health issues. Making any major changes at the wrong time of year can also damage a bonsai tree. The good news is that you can observe warning signs of tree stress or improper care, and you can take proven steps to tend to the tree.
Signs of Dormancy
Winter dormancy starts with cold conditions in fall. These cold nights and days cause deciduous trees to move resources out of the leaves into the branches, causing the leaves to change colors. Conifers also change with cold conditions, often the needle color changes. Conifers pack extra sugar into foliage for winter like anti-freeze to keep cells from forming ice inside. Some tree species require dormancy periods in winter, while others consider it optional. Junipers and tropical species don't really need to go dormant. Many maples and pine trees do need cold weather to go dormant. Make sure you identify your tree's species correctly and provide the right conditions.
Summer dormancy is a reaction to stressful hot conditions. The tiny holes in the leaves called stomata close to reduce water loss in the foliage. This leads to the tree absorbing less water from the soil. Be careful not to overwater during dormancy periods. Carefully check your tree's soil to see if it is drying out over 1-3 days time.
Warning Signs of Tree Stress or Improper Care
Wilted or yellowing leaves are among the most common signs of ill health. This condition is most often caused by overwatering, but under-watering might also be the culprit. There are some fungal pathogens that may be the cause, such as needle blight.
Pests like spider mites can reproduce quickly and be very destructive. Spider mites suck the chlorophyll out of leaf cells (hence, a dulling or yellowing of the leaves.) They love Kishu Junipers, so always check that species! If you find mites, the first thing you want to do is apply weekly soap sprays for a few consecutive weeks, as the soap suffocates the insects (but doesn’t kill the eggs, which is why you need repeated applications).
White spots on trees may be mealy bugs, armored scale or Wooly Adelgids, a sucking insect similar to an aphid. There are a few options when it comes to pest control on bonsai. Watch this video for our recommended treatment for pests like these!
Red, brown, or black spots on tree leaves or needles also likely mean a fungal infection. Watch this video for our recommended treatment for fungal infections!
The roots of your tree will mirror the growth on the top. If the leaves and growth are healthy, your tree has healthy roots. If your tree stops growing, has wilting, yellowing, or dropped leaves, your tree may have dead roots. Root rot is typically caused by fungus (technically oomycetes, “water molds”) that like wet conditions; overwatering or keeping the tree in a situation where it is too wet can cause root rot. Heat stress can trigger root rot. The solution can be fungal treatment, or careful reduction of watering. Let the plant get drier between waterings then soak as normal. A spritz of water to the surface of the soil can balance out evaporation on the surface without making the bottom soggy.
Leaf drop: your tree should not lose leaves out of season. If your tree is losing leaves at the wrong time of year, that may also be a sign of fungal infection. Deciduous trees should lose leaves in middle-late fall. Broadleaf evergreens like olives drop older leaves in late summer. Pines and junipers can drop needles too, usually older shaded or diseased needles are dropped first. A tree that fails to grow new leaves or show healthy new growth is also a cause for concern.
Potential Reasons Your Bonsai Tree May Not Be Healthy
Watering Bonsai: Water is the most important and fundamental aspects of bonsai tree care. One of the most common reasons the health of your bonsai tree may decline is water: whether that’s too much water or not enough water. The amount of water a bonsai needs to thrive is unique for each tree. The quality of your water may also cause problems. Check out this article on water quality.
Sunlight: Another common problem is the amount of sunlight your tree receives. Determining the optimal amount of sunlight needed for bonsai tree health may feel like a guessing game - but it’s not. Generally speaking, keep your trees outdoors as much as possible; aim for at least 4-6 hours of direct sunlight. If your summers are especially hot, the best way to protect your bonsai plants is to place them under a shade cloth to keep them from getting too much sunlight. A common problem many people have is when an outdoor bonsai is brought inside and struggles to survive as an indoor bonsai because of a lack of enough sunlight. Tropical tree species can be kept indoors, though an indoor tree still needs access to lots of light. Natural light is generally brighter and better than any house lighting. Grow lights can be used to augment indoor light conditions.
Using the right type of soil: we recommend two different mixes for bonsai soil, one for early and middle development, and a second for late development and mature trees. Our recommended soil mixture can include perlite, coco coir, akadama, pumice, or lava. Watch this video to learn which soil to use for bonsai and why! We do not recommend adding new soil that is not appropriate for bonsai. Some people use sphagnum moss when potting trees; we use it to increase moisture retention and reduce erosion on rock plantings.
Repotting: There is an ideal time of year to repot a bonsai, and moving a tree into a new pot at the wrong time of year may lead to ill health or tree death. To avoid other issues with repotting remember to use a proper bonsai pot with good drainage holes at the bottom of the pot!
Fertilizer: you can use both organic fertilizers such as E.B. Stone Organics All Purpose Plant Food, OOF, or BioGold (imported from Japan and the very convenient) and mineral or salt-based fertilizers such as Dyna-Gro Foliage Pro, Miracle-Gro, or Osmacote on your trees.
With proper care a healthy bonsai can live a long time: hundreds, if not thousands, of years. Next time a bonsai tree dies, try giving yourself grace; analyze what went wrong with the tree; and learn what to do differently with your next tree.