Repotting Bonsai: Ultimate Guide For Beginners

A bonsai tree is a perfectly formed artists representation of a tree or shrub. The bonsai tree is gently sculpted over time to characterise a full-sized and mature tree that you would find in nature. Typically, bonsais are grown in shallow ceramic pots; they are delicate, fragile miniature trees that require daily attention and regular maintenance.

This extraordinary craft started in China over a millennia ago and has gained popularity in Japan and across the world.

When you care for your bonsai, it’s common to pass your tree through entire generations. Part of the attraction of bonsai growing is that the techniques are an amalgamation of science, art, sculpture, horticulture and the best bit, magic. It’s a different way to appreciate and encourage nature.

When you picture a perfect bonsai in your mind’s eye, you’ll see a perfectly scaled tree or shrub. You’ll have a long-term vision of your scaled tree.

As part of your routine maintenance and care plan, you will want to ensure that your tree is healthy and thriving. Because your miniature tree grows in a small, shallow pot, eventually, it will outgrow the pot and need repotting. You regularly fertilise your bonsai, but the roots will fill the pot at some stage, meaning there are no nutrients consumed, which can result in starvation.

You will need to repot your tree, attend to its root structure and provide a fresh supply of nutrients and soil for your tree to grow and flourish.

Repotting is one of the most crucial techniques for the successful cultivation of your bonsai. You’ll soon understand the importance and how to carry out this critical task successfully. A healthy root system and healthy soil ecosystem are vital to maintaining your tree’s overall health and well-being. When you understand your plant’s growth patterns, you’ll be able to provide a solid and stable growing environment for your tree.

The Importance Of Repotting Your Bonsai

Your bonsai inhabits a small world, and its growth is restricted by a small pot, limited soil and reduced nutrients. A healthy tree can become pot bound quite quickly. As your bonsai grows, healthy roots flourish and replace the soil that once fed them.

If there is no soil, there are no nutrients, and the tree will ultimately starve. It is essential to have a regular pruning programme to remove the older ineffective roots allowing healthy and vibrant new roots to grow in their place.

Your bonsai is pH sensitive and will need to be relieved of any salt and chemical build-up; repotting will also allow for this.

Contrary to popular belief, repotting does not harm or stunt the tree’s growth; it will, in fact, increase growth and benefit the long term health of the tree. When repotting your bonsai, you should remember the original principle of the overall aesthetic of the tree and the pot in which it grows efficiently. Interestingly, there are bonsai in existence that have been growing happily in the same pots for over half a century.

By understanding your plant’s growth patterns and its nutrient needs from the soil, you will respond and repot accordingly.

To survive, plants need water, carbon dioxide, and sunlight to create photosynthesis, which provides carbohydrates such as starch and sugars as food burned in a process called respiration; this drives energy to cells to promote growth. You’ll already know that the air-filled voids in soil feed oxygen to the roots to fuel respiration.

Soil also provides oxygen for the respiration process; if there is a lack of oxygen, the process produces alcohol instead of healthy carbon dioxide and water.

Air-filled porosity (AFP) describes the soil’s capacity to retain air. The denser the soil, the less air it can hold.

Your bonsai grows in a small amount of soil, and the roots can fill the soil’s pores quickly, thus reducing the AFP and amount of nutrients to encourage growth. If the AFP reaches a critically low level, your tree will suffer. In time, the soil will begin to retain more moisture, affecting the air levels to the roots. It’s essential to begin to recognise the signs that your tree needs repotting.

When To Repot Your Bonsai

As a rule of thumb, your young bonsai tree should be repotted each year, whilst the older trees that experience slower growth should be around every three years. You will know when to repot your tree when you look at the root system. When you remove the tree from the pot, and the root ball comes out in one piece, it is time to repot. If fine roots circle the root ball, it is also time to repot, but if the rootball is still surrounded by plenty of soil, carefully re-plant it and check again at the same time next year.

The optimal time to repot your bonsai is in the late winter season, just before it comes out of dormancy. The end of February or the beginning of March is ideal. Repotting and root pruning can cause stress to your tree. It is best to do it during the dormancy period so that it has a little time to recover and heal before the growing season.

By giving your tree time to heal, you will prevent root disease and pest attacks.

During dormancy, your tree is not maintaining fully grown foliage, so damage is minimised.

A good indicator for repotting is when deciduous buds look like they are just about to open. Most pines repot successfully in August when their annual growth has finished. There are a few exceptions; the ficus, pistachio and bougainvillaea prefer to be repotted in the middle of their growing season in the summer.

Remember: Use The Right Soil!!

Choosing the right soil mixture is essential so that you can ensure your tree thrives. As you will have discovered, there isn’t a one size fits all solution. If you are repotting a deciduous tree, the soil should contain 2:1:1 of akadama, pumice, and lava rock. The soil for conifers and pine should contain 1:1:1 of akadama, pumice and lava rock. The soil mixture should allow for essential drainage to avoid root rot and prevent salt build-up.

If you sometimes forget about watering, consider adding more akadama, allowing more water absorption to prevent your bonsai from dehydrating. If you are in a humid climate, add more lava rock to improve drainage.

Choosing the right soil is of paramount importance for the health of your tree. The soil should provide enough drainage and absorption to hydrate the tree. You can purchase specially blended potting soils for your bonsai. Find one that has been double-sifted, so that very fine particles and larger clumps are removed. You can use regular potting soil as part of the potting mix, but not independently.

The soil doesn’t provide good drainage or enough aeration for healthy roots, but as part of the mix, it can help improve texture and help with water retention.

How To Repot Your Bonsai: Step By Step Guide

Treat this as a form of meditation, so why not put on your favourite calming music and have a glass of Japanese saké. Before using your tools, remember that they should be very sharp and thoroughly cleaned with antibacterial wipes or rubbing alcohol to help prevent infection.

Step 1: Find The Right Tools

You will need to invest in the correct tools to manage the growth of your bonsai throughout the various stages of care. You can purchase them individually or in handy kits. Be as gentle as possible when repotting so that you don’t cause unnecessary damage or shock.

Bamboo Rounds

Bamboo rounds or chopsticks are one of the most versatile tools in your repotting toolkit. They allow you to gently manipulate the soil into the tree’s root system to eliminate unnecessary air spaces. You can also use the chopsticks to remove exterior soil and to help free the tree from its pot.

Pruning Sheers

You can use pruning shears to efficiently prune branches and twigs in the tree’s canopy and the roots to ensure a healthy root system. By making fine, clean cuts, you can ensure the best possible healing and root regeneration in the cut areas. You must tease out the roots, adjust their length and prune them to encourage a more refined, ramified root system.

Root Cutters

Root cutters come in various sizes suitable for small, medium and large growth trees. You can use the cutter to shape and create a form to the roots to encourage new growth.

Wire Cutters

If you have used wire on your bonsai, you might find that you need wire cutters to remove tie-down wires to ensure the best aesthetical position throughout the repotting process.

Pliers

You may need to use pliers during the repot if you need to anchor, secure, and tighten any tie-down wires.

Root Rake

The root rake not only loosens the topsoil to promote aeration and water absorption during watering. It can help you remove the tree from the pot and pack new soil to strengthen the tree’s structure during repotting.

Step 2: Cut The Anchor Wire

Older bonsai trees are often secured and anchored to the pot to help hold them in place. If this is the case, you will need to cut the old wire with your wire cutters. Carefully using your fingers or your root rake, begin to loosen the soil so that you can remove the tree.

Step 3: Carefully Remove Your Tree

Carefully remove your bonsai tree from the pot. Young trees tend to be relatively easy, but you might need to use a root saw to separate the bonsai from the pot for much older trees. Separate the root ball from the pot and be cautious not to cut the root ball with the saw.

Step 4: Examine The Roots To Check If Repotting Is Nesscary

When you remove the tree, make sure that the soil is dry. Assess the bonsai roots to see if they are growing around the root ball and the pot. If they are, then your bonsai needs root pruning and repotting to receive more nutrients.

Check the roots for root aphids that suck sap; you can use insecticide to get rid of them.

Step 5: Remove Old Soil

Begin to remove the old dry soil from the roots with your fingers or the root rake; as the soil is dry, it is likely to fall away. Maintain some of the old soil on the roots and add some to the new soil. The root rake can also help you carefully detangle the roots by using careful outwards movements. The bamboo chopsticks can help you release particularly fragile roots. It contains all sorts of beneficial microorganisms.

Step 6: Carefully Prune The Roots

Pruning the old roots will encourage your bonsai to grow better; it encourages root and tree growth. Culling some roots prevents your tree from becoming root-bound and not finding nutrients, water and air. You’ll see that when you start to remove the old soil carefully, fresh new roots are growing from the older roots. Cut back the old roots with root cutters or shears. Remove any rotten or dead roots.

Be very careful not to remove more than a third of the roots. If you are too harsh, you can kill your trees within a matter of days. Cutting back the roots too much will prevent them from absorbing water and nutrients. Avoid repotting your bonsai in the sun; the exposed roots will dry out very quickly.

Keep a spray bottle of tepid water handy to mist the roots as you work.

Step 7: Prepare Your New Pot

Preparation of your new pot is vital so that you can make the transition as quick as possible. The pot must have a drainage hole in its base. Attach the mesh to the pot base to keep the mesh in place by threading aluminium wire from the inside of the pot to the outside, creating a fan to keep it secure.

Once secure, pass two long wires back through the base of the pot to hold the tree in the pot without putting strain on the entire tree.

Step 8: Final Steps

Put a fine layer of gravel at the base of your new pot. Cover with a layer of soil being careful that the cut roots do not come in direct contact with the gravel. Spread the roots upwards and outwards to the sides of the pot when placing the tree.

Be mindful of the placement of the tree in the pot and plant non-symmetrical trees off-centre.

When you place the tree back in its pot, use the new wires to hold the tree in place. Gently fill the pot with your bonsai soil. Use your chopstick to work the soil around the roots, making sure to fill all the air pockets around the root system. Press firmly with your fingers to facilitate secure roots.

Once compacted, place the pot in the sink so that the new soil is moist.

Decorate the top with gravel or sand to help maintain the moisture levels.

Repotting Bonsai: Your Top Questions Answered

Will Repotting Kill My Bonsai?

You need to ensure that you follow the instructions carefully, prudently plan your repotting experience and don’t rush the process. You can quickly kill your tree if you over-prune the roots or use the wrong soil mixture. After-care is also essential.

Ensure that you keep your tree in partial shade and water it properly, careful not to overwater the fragile roots.

Do I Water My Bonsai After Repotting?

Yes, but be careful not to overwater the tree. It needs to be kept in temperate conditions for a couple of weeks to recover fully and for new growth to emerge.

Should My Pots Have Drainage Holes?

Yes, they do. All ceramic bonsai pots must have drainage holes. Usually, there are two holes that you will need to cover with mesh so that the soil doesn’t leak away. Larger pots sometimes have more holes.

Can I Repot My Bonsai In The Summer?

Dormancy helps protect your tree against shock and untimely death. Bonsai experts recommend that you plan your repotting jobs each spring. Some species prefer repotting in the summer months, but as a rule of thumb, stick to the spring. Emergency repots can be carried out at any time if absolutely necessary.

Should I Fertilize My Bonsai After Repotting?

Many different health elements can benefit the overall well-being of your bonsai. You must repot your plant between every one, and three years depending on its age. It is essential to maintain regular liquid and slow-release fertilisation programmes based on the time of year.

Be aware and check to see if your tree is actively growing or in its dormancy period.

Experts do not recommend that you fertilise your bonsai immediately after repotting. Your tree will be fragile and susceptible to fertiliser burns. Allow your bonsai to settle and heal for three to four weeks or until you start to see healthy new growth.

Avoid any excess stress to your bonsai so that you can allow it to recover fully and start to grow with vigour again.

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