Beginner bonsai enthusiasts often ask this question “when does a bonsai need repotting?” or “When to repot bonsai?“.
Well, when it comes to bonsai repotting, it’s hard to set general rules. It depends on the condition of the bonsai tree (healthy or not), bonsai tree species, shifting to a new pot or the climatic conditions where you are growing the bonsai tree. Also, whether it is an indoor bonsai tree or an outdoor bonsai tree.
For example:
- In temperate regions, trees are typically repotted and root pruned during the dormant season, i.e. winter or about four to five weeks before spring growth is apparent (early spring). It is also common for sub-tropical trees to be repotted during the coldest season. In contrast to temperate trees (deciduous trees), their dormancy period is shorter. However, root pruning them when they are less active is safer.
- On the other hand, Unlike subtropical or temperate trees, tropical trees can be repotted almost anytime throughout the year. However, I would advise you to do the repotting at the same time as temperate and subtropical trees.
- Apples and cherries that bloom in spring should be repotted in early fall, and azaleas and quinces should be repotted immediately after they have finished flowering.
- In case of indoor bonsai trees, I would recommend repotting in late spring as early spring is too cold to disturb the roots of indoor bonsai.
Generally speaking though, bonsai repotting is mostly done during early spring, when the tree is still dormant. By doing this, the somewhat damaging effects of repotting on a tree are reduced to a minimum since the tree does not yet have to sustain its full foliage. In addition to this, repotting the bonsai tree in early spring also ensures that the healing process of pruned roots starts early. This is because the growing season of the tree is coming soon.
It is also worth noting that in the art of bonsai, the term “spring” does not necessarily refer to the season which begins on 21 March, but rather to when vegetative growth resumes and buds begin to form.
Following table shows the repotting and root pruning season of some of the bonsai trees (38 bonsai species listed):
| Genus | Name | Repotting and root pruning |
|---|---|---|
| Abies | Fir | Spring |
| Acer | Maple | winter-Spring |
| Bamboo | Bamboo | Spring-Summer |
| Camellia | Camellia | Spring-Summer |
| Cedrus | Cedar | Spring |
| Celtis | Hackberry | Winter-Spring |
| Cbaenomeles | Flowering quince | Spring |
| Chamaecyparis | False cypress | Any time |
| Cornus | Dogwood | Spring |
| Cotoneaster | Cotoneaster | Spring-Summer |
| Crataegus | Hawthorn | Spring |
| Cryptomeria | Cryptomeria | Spring |
| Cupressus | Cypress | Spring |
| Diospyros | Persimmon | Spring-Summer |
| Fagus | Beech | Spring |
| Fraxinus | Ash | Spring |
| Ginkgo | Maidenhair tree | Spring |
| Hedera | Ivy | Spring |
| Ilex | holly | Spring |
| Jasminum | Jasmine | Spring-Fall |
| Juniperus | Juniper | Spring |
| Larix | Larch | Winter-Spring |
| Malus | Crabapple | Spring-Fall |
| Picea | Spruce | Spring |
| Pinus | Pine | Spring |
| Prunus | Flowering fruits | Winter-Spring |
| Punica | Pomegranate | Spring-Summer |
| Pyracantha | Firethorn | Spring |
| Quercus | Oak | Spring |
| Rhododendron | Azalea | Spring-Summer |
| Salix | Willow | Spring-Summer |
| Tamarix | Tamarisk | Spring |
| Taxus | Yew | Spring |
| Thuja | Arborvitae | Spring |
| Tsuga | Hemlock | Spring-Summer |
| Ulmus | Elm | Winter-Spring |
| Wisteria | Wisteria | Spring |
| Zelkova | Sawleaf zelkova | Winter-Spring |
How often should I repot a Bonsai?
It is important to note that bonsai repotting frequency is heavily influenced by the species, size, size of the container and age of each individual tree.
For instance, fast-growing species such as fig tree may need repotting every year, whereas slower-growing trees such as black olive tree may require repotting every three to five years.
You can refer to the types of bonsai tree page for specific details about repotting needs of a specific tree. Regardless of these factors, the bonsai repotting method remains the same.
Mature bonsai do not require repotting as frequently as young trees because they grow more slowly and do not become root-bound as quickly. Also, trees potted in shallow containers might require more frequent repotting when compared to bonsai trees potted in large and deep containers.
Normally, conifers are repotted every two to three years, while deciduous and evergreen species are repotted every year or two.
Warm climate bonsai require repotting more frequently than those grown in colder climates (every 2-3 years in a temperate climate to every 5 years in a cool climate).
Do not stick to a fixed routine of repotting your bonsai. be flexible and only repot the bonsai when needed. There is no need to re-pot bonsai trees unnecessarily, as it is likely to cause the tree some considerable shock and trauma.
How do i know if my bonsai needs repotting
If a bonsai has been neglected for many years, you will notice a few things in your bonsai tree:
- Roots emerging between the potting mix and the inner wall of the container. These thin roots are not the same as the old ones growing at the base of the tree.
- Roots sprouting out of the drainage holes at the bottom of the pot
- Decline in the health of the bonsai tree (such as unexpected falling of leaves or discoloration of leaves, weak shoots and branches etc)
- A healthy amount of leaves during the growing season indicates a healthy root system. This is a fairly reliable indicator whether you need root pruning and repotting.
- Tree not responding well to watering and feeding
- Slow passing of water through the bonsai soil
All the symptoms listed above indicate that you must repot your bonsai.
In order to be absolutely sure that your bonsai tree does indeed need to be repotted, you should tap it gently around the side of the pot and then hold it upside down and carefully remove the pot from the root ball. As you are doing this, if large pieces of soil begin to fall out of the pot, then you will know that your tree does not need to be repotted. However, if after removing the pot, the root ball is almost solid and covered with roots, then it is definitely the case that the plant ought to be replanted.
Early spring is a good time to check the roots and determine whether your bonsai needs repotting.
Follow how to repot a bonsai tree instructions to repot your bonsai tree.
Will repotting a bonsai kill it
No. repotting a bonsai will never kill it. Provided you have taken care of all aspects of the repotting process. By using the right bonsai soil, making sure that the bonsai soil is disease and pest free and giving the correct after care after repotting, you can make sure that the bonsai tree survives.
Read how to make your own bonsai soil to know more about right bonsai soil for your bonsai tree.
Also read the last section of bonsai repotting to know about the after care of a repotted bonsai.
Many people think that the act of root pruning might kill the bonsai tree as it looks so drastic. However, you must remember that contrary to popular belief that root pruning will have a dwarfing or stunting effect on the tree, root pruning enables the tree to grow more strongly.
This is because root pruning will result in the production of more new feeder roots. Whenever a root is cut, a number of new fibrous roots emerge from the cut. This increases the amount of feeder roots needed to maintain the good health of the tree.
Repotting bonsai in fall
It is possible to repot bonsai during the fall season. It depends on the type of the bonsai tree. For example, some of the bonsai tree species like crabapple and jasmine can be repotted easily in fall. This does not mean that all types of bonsai trees will respond well to repotting in fall.
Keep in mind that if you prune the roots in fall, the roots will have to endure the rigors of winter before they can begin to heal. The risk of root dieback and decay will be greatly increased.
Should you decide to repot your bonsai in the fall season, make sure that you keep your bonsai in a protected frost free location and keep the watering to a minimum till the spring season.
Repotting bonsai in summer
Repotting a bonsai tree in summer depends on the type of bonsai tree species. Bamboo, Camellia, Cotoneaster, Persimmon, Pomegranate, Azalea, Willow and Hemlock can be repotted in summer (between Spring-Summer). On the other hand, some trees such as Pine or Juniper prefer repotting in spring before the buds open.
Also, most of the tropical indoor bonsai trees can be repotted in early to mid summer (in the middle of their growth period). However, this does not hold true for subtropical indoor bonsai trees. These are repoted in spring before the new growth starts.
Understand the bonsai species you are growing and know whether it can be repotted in the summer. With experience you will learn if your favourite tree species can sustain the stress of repotting in summer.
I will suggest not to perform repotting in summer if you don’t have to or if you are not sure. However, if you still wish to perform it, then practice it on a test bonsai subject and see if you can maintain the tree.
It is critical to know what a tree does in summer so that you have a better understanding of whether to repot the bonsai in summer or not.
Most bonsai trees are actively growing during the summer months, and their roots are doing their best to provide the tree with enough nourishment and water to sustain growth. When you prune the roots and repot the tree at this time, the tree will go through a lot of stress. This is because suddenly after repotting you will be moving the tree to a sheltered place and reducing watering.
Repotting bonsai in winter
Many bonsai tree species such as Maple, Hackberry, Larch, Elm, Sawleaf zelkova and flowering bonsai trees can be repotted in winter.
However, whenever in doubt as to when to repot your bonsai, your safest bet will be repotting the bonsai in spring few weeks before the new buds open.
Can you repot bonsai in the same pot?
If you want to repot an mature indoor bonsai, you can use the same pot, unless you want to change it for aesthetic reasons.
For young and vigorously growing bonsai trees, however, you will need a new pot roughly 2 cm bigger than the old pot every one or two years. Take this as a general guideline, you can take even bigger pot. It all depends on the size of the bonsai tree.
Also, every time you repot on the same pot, make sure that you clean it thoroughly before repotting.
How much roots are trimmed in bonsai?
If you are a beginner and unsure how much root pruning is needed, the best rule of thumb you can follow is to remove 20-30% of the fine root hairs.
It is important, of course, to remove just the right amount of roots each time the bonsai tree is repotted, and that requires a delicate balance between removing the right amount of roots at the right time.
If you prune too much of the roots mass, the tree will die, since it will not be able to absorb enough water to maintain an adequate level of hydration.
On the contrary, pruning too little roots will result in the roots spreading out further, and the bonsai will have to be moved to a larger container as the roots will continue to grow.
Benefits of repotting bonsai
- Repotting enhances soil texture and quality: Over time, soil in a pot breaks down. Seasonal changes, daily maintenance, and thick, aging roots reduce soil porosity. Also, the pH of the soil is changed. Repotting allows plants’ roots to receive sufficient oxygen: Old soil’s increasingly fine texture prevents plants’ roots from receiving adequate oxygen. During watering, fresh, porous soil helps in circulation of oxygen to the roots. Fresh soil also has the right pH level for the bonsai tree.
- Repotting aids nutrient absorption: It is impossible for new roots to grow when a bonsai is pot-bound, as there is no room for growth of new roots. After root pruning and repotting the new roots are able to absorb nutrients efficiently.
- Repotting helps in water retention: As the soil gets older, its water holding capacity reduces. Changing the soil with fresh porous soil at the time of repotting helps in water retention.
- Repotting prevents pests and diseases: The process of repotting not only involves changing the soil but also inspection of the root system. At this point, decayed or dead roots can be removed. Hence, changing old soil and removal of bad roots reduces the chances of diseases and pests.
- Repotting helps in controlling the size of the bonsai: Root pruning is essential in controlling the size of your bonsai tree. In general, the more roots a tree has, the bigger it can become. Hence, root pruning and repotting the tree in the same pot will help in maintaining its small size.
- Repotting can be used to change the aesthetics of the bonsai: If you plant to change the bonsai pot, repotting is a good time to do it. Read choosing the right bonsai pot for more details.
