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How To Properly Take Care Of A Bonsai Tree

How To Properly Take Care Of A Bonsai Tree
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Many people buy or are gifted a bonsai, only for it die within a year. Learning how to properly take care of a bonsai tree is really important to help your trees not just survive, but thrive, while also pushing forward their design and making them look as good as they can.

Here's what you need to know:

How to care for a bonsai tree

How to care for a bonsai tree

Knowing how to take care of a bonsai tree comes down to two things - intention and knowledge.

When caring for a bonsai tree, you need to have a clear plan for how you want the tree to progress. For many, this can be as simple as keeping the tree's general shape and controlling growth. For others, it might be a radical redesign with branch removal and deadwood carving.

It doesn't specifically matter what the plan is, but you need one in order to guide your actions through the year. If you don't repot, prune, wire or fertilize with your primary goal in mind, the results for your tree could be different from what you wanted.

Once you have a plan, you need the horticultural and artistic knowledge to execute it in order to keep your bonsai healthy and progressing towards your goal.

How much care do bonsai trees need?

Bonsai tree care varies through the year, but it is something that you will need to think about on a daily basis if you have even a small collection.

The biggest part of bonsai care is watering, which is something you'll need to do at least once per day through the growing season. Watering your trees is a great opportunity to check them over and look for signs you need to provide other care such as pruning, repotting or pest control.

Repotting is an activity that is only required every few years for each tree, and should only be performed at one time in the year (late winter / early spring). If you have a small collection, repotting isn't usually too much of a time burden.

If like me you have a larger collection, then springtime can involve some long days in the shed. (I don't want that to sound like I'm complaining, repotting is one of my favourite things to do!)

Pruning and wiring are often performed together and generally aren't needed more than a couple of times per year depending on the species you are looking after.

All in all, if you can get your head around the fundamentals then the amount of care a single bonsai tree needs is quite small. But as your collection grows, that's where the fun begins!

Watering your bonsai

Watering is a technique that many new practitioners underestimate the complexity of. Bonsai are cultivated in a confined environment to achieve the desired reduction in leaf size and restriction of growth that creates nature in miniature, but the small container makes watering much more difficult.

Bonsai watering care

The key to providing the best care for your bonsai via watering is to achieve the perfect balance of water and oxygen in the pot.

Roots need oxygen as well as water to thrive. Overwatering your bonsai can be just as bad as underwatering it, but the negative effects will take a long time to show. A lack of oxygen in the root system can cause roots to die and lead to the development of root rot in your bonsai.

The idea with watering a bonsai tree is to very thoroughly water the pot until the whole of the root ball is fully saturated with water. In general, you should avoid watering the foliage where possible, because this can encourage the spread of fungal diseases.

Once the root ball is wet, you should leave it until it starts to dry out again. You should check your trees periodically to determine if they need to be watered again. You can decide this based on:

  • the size of the pot
  • species of the tree
  • soil composition
  • weather
  • moss
  • your lifestyle (when can you next water?)

We've created a bonsai watering checklist to help you work out if you should apply water.

Repotting

Repotting is a crucial activity in taking care of your bonsai tree. The small containers used in bonsai cultivation are important for restricting growth and reducing leaf size.

It's important to understand when to repot your bonsai and also how to repot it to make the best use of the container while also not leaving your tree in the pot for so long that it starts to lose health.

How to know if your tree needs repotted

There are three markers you can use to help you decide if your bonsai needs to be repotted.

  • Change of aesthetic - This includes changing the pot, changing the front of the tree or changing the planting angle.
  • Loss of percolation - If you water your bonsai and the water runs off the side rather than flowing through the soil, then you have a loss of percolation. When this becomes so severe that you can no longer water your tree properly, you need to repot.
  • Soil decomposition - Soil in your bonsai container will break down both actively (via root growth) and passively (through watering, microbial activity etc.) over time. As the soil particle size increases, it starts to hold more water and have fewer oxygen spaces. Once your soil becomes muddy and stops drying out properly, it's time to consider a repot.

These criteria are a very good guide for letting you know if your tree needs a repot. If you don't follow these, you might be repotting your tree too frequently.

If you repot your bonsai before it has filled the pot with roots, you are missing out on the benefits of the constricting container. Roots will be thicker, and as a result, your tree's foliage will be coarser.

You are unlikely to risk the health of your bonsai by repotting too frequently, but you will find it much harder to cultivate a refined bonsai.

Bonsai repotting care

When to repot

Almost all trees benefit from repotting in late winter or early spring. The key indicator you should be looking for is bud swelling.

Swelling of the buds shows you that your tree is coming out of dormancy and getting ready to grow. Once your tree is actively growing new foliage, it is generally considered too late to repot. You can still repot many young or healthy trees after foliage growth has started, but you should be aware that there is a risk that the bonsai won't make it through the repot. I would advise against repotting out of season.

How to repot

There are a few general steps you need to follow when repotting your bonsai tree. It's important to always be intentional with your actions - don't start impulsively removing soil from the root ball as it may be something you later realise you should have preserved.

The approach you should take is this:

  1. Remove the tree from the pot. Use a root sickle to free the edges of the soil mass, cut any tie-down wires, and then pull the root ball out of the pot.
  2. Remove moss and soil from the top of the root ball to reveal the nebari (flaring root base).
  3. Reduce the height of the root ball by working from the bottom up, first by removing the matted roots on the bottom and then scraping away soil with a chopstick. Make sure you mould the base of the root ball to your desired planting angle. Focus on areas of black or smelly soil, as these can negatively impact the health of your bonsai.
  4. Remove matted roots from the sides of the root ball.
  5. Prepare the pot - add drainage screens and tie-down wires. Ensuring your tree is immobile in the pot is vital for new root growth and success in repotting.
  6. Add a small mound of soil to the pot and add the tree. Tie it in with your tie-down wires and fill the pot with soil.
  7. Use a chopstick to put soil into any air pockets.
  8. Apply a topdressing of ground sphagnum moss and ground green moss to protect the soil surface.
  9. Water the tree very thoroughly to wash away any crushed soil particles.
Non-glazed bonsai pot

Pot Selection

There is no right or wrong answer when choosing a pot for your bonsai tree. Bonsai is an art form, so you should choose whatever container you feel brings interest to the tree and that brings you enjoyment.

If someone disagrees with the aesthetics of your chosen pot that's fine - beauty is in the eye of the beholder.

I don't want to write any 'rules' for pot selection, but there are some guidelines you can follow to help you to think about the impact of different pots on your tree.

There are two things you need to think about when choosing your pot - form and function.

Bonsai pot aesthetics

Some conventions are often followed when pairing a bonsai with its container. These have come about because they generally look good, but as already stated they are not rules so do not feel you need to strictly adhere to these.

Firstly, for evergreen trees, a non-glazed container is traditionally used. This is because conifers generally base their value around the impression of age, and a dull, toned-down ceramic can complement this.

In contrast, deciduous trees (broadleaf deciduous or deciduous conifers such as larch) can pair well with glazed ceramics. Deciduous bonsai, with their seasonal nature, often have a younger form. The shine and vibrance of a glazed container can complement the tree well, particularly during the winter when it can add colour to a leafless tree.

With glazed containers, we can also play on colour. You can choose a pot colour that either matches or contrasts differing parts of the tree, whether that's fruits or flowers, the summer or autumn foliage or the colour of the bark. There are a lot of options to think about and play with.

Glazed bonsai pot

As well as glaze we need to consider the shape of the pot. A thick, craggy trunk will generally suit a more angular and straight-walled pot. A slim and elegant tree will usually look nicer in a lighter and more curved container.

Bonsai care with containers

While a pot may look perfect for a tree, we also have to consider the impact it will have on how we care for the bonsai.

The smaller you go with the pot, the more watering you will need to provide through the growing season and the more protection you will need to give during cold winters.

The are some general, well-known guidelines in the bonsai community for sizing. These should be used as a starting point, but you must also consider specific factors for the tree such as age, vigour and whether you wish the tree to flower or fruit. For each of those factors, you may want to increase the size of your pot.

Also bear in mind that your lifestyle should influence your choice of pot. If you are out at the office all day and can't monitor your trees' water requirements closely, you may want to keep them in larger pots to avoid them drying out on hot summer days.

General pot sizing guidelines are as follows:

  • The depth of a pot should be equal to the diameter of the trunk just above soil level
  • If the pot is oval or rectangular, aim for its length to be 2/3 the height of the tree
  • If the pot is round, aim for its diameter to be 1/3 the height of the tree

Pruning

Pruning is a really important activity in caring for and maintaining a bonsai tree. There are two types of pruning you can perform - structural pruning and maintenance pruning.

Structural pruning involves selecting branches and creating the design of the bonsai. It involves making big cuts and big branch removals, sometimes even cutting the trunk of the tree. The other type of pruning is maintenance pruning which is necessary to maintain the shape of the tree after it is in style.

As you can probably guess, maintenance pruning involves maintaining the shape of the bonsai and encouraging interior growth. This interior growth helps to grow the body of the tree's foliage mass and increase ramification.

Bonsai pruning care

Structural pruning

Structural pruning can be done at various times during the year depending on the species of the tree. The most common times would be in spring just before growth, or in autumn - either early autumn for conifers or late autumn after leaf drop for deciduous trees.

When working with deciduous trees we need to consider whether or not the species may bleed sap when pruned. For example, Japanese maples have a high propensity to bleed sap if pruned in the spring and for this reason, the structural prunings are generally done after leaf drop in autumn.

Maintenance pruning

How you manage the foliage of a tree through the year very much depends on the species you're dealing with.

For most deciduous trees you will need to prune regularly through the year with pruning shears. After growth starts in spring, let the first flush grow freely and harden off. You can tell when a leaf has hardened off by a deepening of the green colour and the appearance of a waxy coating over the leaf.

Once this has happened you can then prune back to 2 or more buds. These buds will then push growth again and you continue this process throughout the growing season.

The reason for cutting back to 2 buds is to encourage more branching. If you do not prune in this way regularly then strong leaders will take strength away from weaker branches which will then die off.

When handling coniferous trees, there are a few different approaches to take.

For some deciduous conifer species such as larch, you follow a similar pattern to deciduous broadleaf trees, where you let growth push out and then prune back to 2 buds.

Species such as spruce should be pinched when they start to grow past the desired silhouette of the tree. Pine trees can also be pinched in a similar way.

Junipers should be pruned once or twice through the year with pruning shears. They should not be pinched as this can disrupt the hormonal distribution across the tree.

There is a great deal of complexity in pruning that is very species-dependent. Please read up on the species you're dealing with to make sure you're working off sound principles when pruning your tree.

Wiring

Similar to pruning, wiring your tree is a very important activity for developing the style and design. Wiring can be discussed in terms of structural wiring and pad wiring.

Bonsai wiring care

Structural wiring involves setting the so-called 'bones' of the tree. This involves shaping the trunk and primary branches of the tree. A primary branch is any branch that originates from the trunk of the tree.

Pad wiring involves shaping the secondary and tertiary branches that originate from the primary branches and establishing pad size and orientation.

As discussed with pruning, styling generally takes place in spring before growth starts or autumn. Wiring is something that you will likely need to do in some form throughout the lifetime of your bonsai, but the amount of wire you'll need to put on your tree will lessen over time as branches set in the correct position.

Structural wiring

When setting the structure of a tree, the approach you take will depend on the size of the material.

When dealing with very large bonsai it is often impossible to shape the trunk with the wire and we need to use other techniques such as wedge cuts and trunk splitting. These are rather advanced techniques and they are topics that are too in-depth to cover in this post.

For smaller material, using thick gauge copper wire should allow you to bend the trunk to the shape you want.

Wire should be applied at a 45-60° angle to the trunk, wrapping it counter-clockwise or clockwise depending on the direction you wish to bend. If you're bending to the left you should wrap your wire clockwise so it can tighten as you bend and vice versa.

If you're wiring the trunk on its own it is often helpful to push the wire down through the soil to the bottom of the pot to stabilise it before you wrap it around the trunk.

When wiring primary branches it can be helpful to pair branches together so one piece of wire spans two branches. If you do not have a suitable branch pair, you could also create a hook around a piece of deadwood to anchor your wire.

When bending be sure to watch the branch carefully for the focal point of the bend. This will be the point on the branch where the largest area of force is being applied. You will see stretch marks and very small splits appear on the branch just before it breaks. This means you have pushed the branch to its limit and you shouldn't risk bending it any further (unless you're very experienced and know what you're doing).

Another wiring technique you can use to set structure is the use of guy wires. This is where you wire a branch to another without wrapping wire around the branch. You can then tighten the guy wire to bring the branch down to the desired position.

Guy wires are effective for moving large branches and they are commonly used for deciduous trees to reduce the risk of wire scars on branches.

Structural wiring should start as early as possible in the life of a bonsai. This is so you can take advantage of the trunk being small and flexible to reduce the risk of breakages.

Bonsai pad wiring

Pad wiring

Once you've set the structure of your tree you'll need to wire the smaller branches into position to form pads (or billows if you are styling a deciduous tree).

As with structural wiring, we can make use of branch pairs to anchor the wire. Use wire and pruning to create pads with clean, flat bottoms in coniferous trees.

For deciduous trees, use a minimal amount of wiring to create billowy pads. Deciduous bonsai can often be handled with pruning alone once their primary and secondary branches have been set.

Wiring aftercare

Once you've applied it, how long you leave wire on a bonsai tree will depend on whether you're dealing with a thick- or thin-barked tree.

For thick-barked trees, we usually leave the wire on until you see evidence of wire biting into the tree. This means the tree has grown enough tissue in its new position and will likely hold when you remove the wire.

With thin-barked trees, if you let the wire bite into the branch this will often leave a scar which can take decades to heal. For this reason, we don't let wire dig into thin-barked trees. You need to watch carefully and remove any wire when it starts to look tight. Because wire stays on the tree for less time with thin-barked trees, you will likely need to reapply wire to continue developing your bonsai.

Fertilizing

Fertilizing is very much a misunderstood practice for many bonsai tree owners. Fertilizer can greatly benefit your trees if you use it appropriately but can hold them back or damage their health if used at the wrong time or in the wrong quantities.

To start, let's clear up what fertilizer is. Many people believe fertilizer is 'food' for bonsai trees, but this is untrue. Trees create their 'food' (e.g. sugars) via photosynthesis. Bonsai trees can and do survive very well without fertilizer.

Fertilizer is a blend of nutrients and minerals that are used to promote growth.

So now we have that established, the question you need to ask yourself is why am I fertilizing this bonsai tree?

Reasons to fertilize

Fertilizer is a tool to help us build our bonsai, so its use needs to be aligned with our goal for the tree:

  • Growing the tree larger, developing branches and thickening the trunk - fertilize heavily
  • Encourage multiple flushes of growth to enable partial defoliation to improve ramification - fertilize moderately
  • Maintain growth and vigour in a long-established bonsai - fertilize lightly

You should only apply fertilizer once you have worked out a development plan for your bonsai.

If you have a nicely refined bonsai and you start fertilizing heavily, you will get coarse growth which will ruin the fine ramification you have already achieved. Equally, if you need strong growth and development but only fertilize lightly, it will take much longer to get the results you are looking for.

When to stop fertilizing

Plant fertilizer contains a very high salt concentration which can be detrimental to your bonsai tree if applied at the wrong times. If you think your bonsai matches any of the conditions below, I would take great care before considering fertilization.

  • Recently repotted bonsai trees - Avoid fertilization for 2-3 months as cut or torn roots will be vulnerable.
  • Overwatered bonsai trees - Roots can become weak and die off as a result of overwatering. Improve your watering and let the tree gain strength before fertilizing.
  • Unhealthy bonsai trees - if your tree has a fungal infection, for example, it may be due to weakness in the roots. Let the tree recover before fertilizing.

Placement

Knowing where to place your bonsai trees is key to their well-being. Some trees can be grown indoors, some must be outdoors, some need shade while others love as much sun as possible.

Keeping bonsai indoors

Whether or not you can grow your tree indoors is a very common question for beginners. Many bonsai trees are sold as 'house plants', when in fact they are small trees that need to live outside to survive long-term.

Some trees can be grown indoors, which is great if you want to enjoy your trees as a feature in your kitchen or living room. These trees are generally tropical plants or plants that enjoy a warm climate. Some of these include:

  • Ficus
  • Jade
  • Fukien Tea (Carmona)
  • Hawaiian Umbrella (Schefflera)
  • Sweet plum (Sageretia)
  • Chinese elm (Ulmus)

The popular species have been tried and tested as indoor bonsai so you can be confident that given the right care, they will thrive in your house. Many of these trees are some of the best bonsai tree types for beginners because they are easy to care for and style.

The reason most indoor bonsai trees are tropical trees is they do not require winter dormancy.

Almost all temperate trees need a period of dormancy over winter to prepare for the next cycle of growth that will begin in the spring. Dormancy is triggered by decreasing temperatures and a reduction in daylight length, which is very hard to replicate in an indoor environment. Most temperate trees are therefore better kept outside.

Keeping a bonsai tree indoors is not necessarily the same as caring for a houseplant. Bonsai are planted in small containers to restrict root growth, which has a big impact on how you water them. On top of this, since most indoor bonsai are tropical plants you need to take into account their requirements for warm temperatures, a lot of light and high humidity levels.

Temperature requirements for indoor bonsai

Tropical plants benefit from quite warm temperatures throughout the year. A comfortable temperature in your living room is probably good enough for most plants, but ensuring it remains constant throughout the year can be a challenge.

If you live somewhere with cold winter nights, make sure the room you keep your bonsai in over the winter doesn't drop in temperature too much. If you usually keep it in your kitchen, it might be advisable to place it somewhere warmer such as your bedroom or living room over the winter months.

If you are growing a temperate tree such as a Chinese elm indoors then keeping it somewhere where it can get a bit colder in winters, such as a kitchen or utility room, could help the tree a lot.

Light requirements for indoor bonsai

Placing your bonsai where they can get enough light is one of the biggest challenges of cultivating trees indoors.

Light intensity is much less indoors than outdoors, which can impact the health of your tree over time. Most trees will be fine for several months or years, but if your bonsai isn't getting enough light it will slow down its growth and eventually weaken the plant.

Placing your bonsai directly in front of a window, ideally a south-facing window, can help the health of your tree.

Humidity requirements for indoor bonsai

The humidity of the air in your house is likely to be very low (meaning the air is dry) compared to outside.

Indoor bonsai require higher humidity levels to stop them from losing too much water and drying out too quickly.

To help achieve this, consider placing your bonsai over a humidity tray filled with water or misting the foliage a few times each day. Placing your bonsai by a window can help here too because you can open the window when it is warm enough outside to circulate some higher-humidity air from outdoors.

Keeping bonsai outdoors

Most bonsai trees should be cared for outdoors. Bonsai trees are genetically just regular trees.

There are a very wide variety of trees that you can cultivate as outdoor bonsai and many of them can have quite different requirements when it comes to light/shade, humidity and temperature tolerance. If in doubt, pick a tree that grows natively near you as you can be fairly sure it will cope well with your climate.

The placement of your tree outdoor will depend on the species. Some trees, such as pines and junipers, prefer as much sun as possible. Others, such as some deciduous trees, may prefer shade for periods of the day.

Light requirements for outdoor bonsai

Where to place your bonsai in your garden to give it the best light exposure will depend on the species and the condition of the tree.

The advice here is a generalisation, so be sure to check specific guidelines for the species of your bonsai when deciding where to put it.

In general, conifers such as pines and junipers prefer a lot of sunlight and warmth. A lot of deciduous trees like a half-day (morning) of sun or dappled shade, although some grow very well in full sun.

Temperature requirements for outdoor bonsai

This will very much depend on where you live. If you live somewhere without extremes of temperature (either high or low) then you probably don't need to worry too much about this. However, many people grow bonsai in places where temperatures can be either very high during summer or very low during winter. In each of these cases, you'll need to manage your trees.

If you have very hot summers, consider a shade cloth for your trees on hot days to keep them cooler. If you experience extremely hot summers and can't shade your trees, you may want to consider wrapping foil around your pots to reflect some of the sun's rays and stop any roots in contact with the pot from overheating.

If you experience very cold winters, you'll need a strategy on how to care for your trees when temperatures drop below freezing. Most temperate trees can tolerate temperatures around freezing with little issue, but below that, some species of tree will need protection.

Protecting your trees over winter can be achieved by placing them in a greenhouse, burying pots in leaves or mulch or placing bonsai in a windbreak shelter. The severity of the weather and the vigour of your trees will guide you.

How do you care for a bonsai tree?

As you can see there's a lot to think about if you want to know to how to properly take care of a bonsai tree.

There's a lot of info here, so make sure you bookmark this page and come back to it as a reference.

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