How to Repot a Bonsai Ficus Plant

Last year I purchased a bonsai ficus retusa and over the past year it has become side heavy, leaning to one side and pulling itself out of the soil. The tree leaves themselves are flourishing and look amazing, drinking in the warm sunlight from its tranquil spot in front of my south facing window. The severe lean that is causing the roots to be exposed, however, has me concerned that this tree may soon find itself in distress. An intervention is needed!

For most houseplants, the going wisdom is to repot in early spring, but the timing for repotting a bonsai tree depends quite a lot on the specific type of tree. (And it’s important to note that bonsai plants are miniature trees, and not a typical houseplant.) My specific type of tree—as mentioned previously—is a bonsai ficus retusa, so my timing for repotting this plant is not in early spring, but in mid to late summer. 

This is possibly an over-simplified overview of when to repot the bonsai ficus, however, and it’s only fair to share just a little of the abundance of information I have found on the topic. I have actually found (frustratingly) that there are different opinions on the topic, but much of how you care for your bonsai ficus will depend on a few key points: 

• the specific species of tree
• the age of the tree
• your climate
• whether or not your bonsai is an indoor or outdoor plant

According to one source–Bonsai Empire—you should avoid replanting bonsai trees in summer or winter, however other sources indicate that indoor plants are less vulnerable to the changes in the season and will tolerate repotting at other, less ideal, times of year.

As with floral arrangements in vases, the pot of the bonsai should be 1/3 the height of the tree.  You may need a pot that is 2/3 the width of the tree as well to create the right balance, forming a triangular shape to your display. If you are shaping your bonsai you are probably using triangular geometry in your design, so keep this in mind when choosing a pot.

Now that we’ve addressed the pot for the bonsai tree, let’s talk about soil. What type of soil will you need for your bonsai ficus? Just like I mentioned before, there are different schools of thought depending on who you ask, but Below are a few suggestions from my research:

• bonsai soil mix
• lava rock and pumice (lava rock helps with draining), 
• Akadama (soil containing clay)
• leaf mould
• bark, along with soil that contains humus

I have also been told that cactus soil is good to use in a bonsai soil mixture for its drainage properties. It’s a good idea to tailor the soil mixture to the type of tree and the level of humidity in the environment, and overall you just want a well draining soil. You want your soil to hold just enough moisture for the tree to thrive but not be sitting in soggy soil. For my mix I used a mixture of what I had on hand—cactus mix, sphagnum peat, potting mix, and orchid bark. For the fungicide (for the branch I cut off and potted) I used a TBS of apple cider vinegar in 1 cup of water.

The root ball of your bonsai tree will need to be carefully manipulated and unraveled during this process. Carefully unravel the root ball, rake out the old soil using your fingers or a small rake so you can stretch out the roots for pruning (see the next section for trimming instructions). Once the roots are prepped you can start adding in a layer of soil or drainage rocks, feed in the wire that will hold the tree in place, place the tree in the soil, carefully work new soil in between the roots, then add soil to fill the pot. Wire the tree into place (we’ll discuss later) and water thoroughly.

After the soil has been raked out and roots have been carefully loosened, it is time to assess how—and if—the roots get trimmed. Kaizen Bonsai recommends trimming roots according to the tree species and relative to the condition of the tree and roots at the time. If in doubt, or if the tree is not doing well, maybe err on the side of caution and not bother the roots this time around. 

Why trim the roots, you might ask? Giving the roots a hair cut (root pruning) while replanting helps stimulate new growth. This process will help the tree get water and nutrients faster. When doing this process, however, don’t get too carried away—only cut up to 1/3 of the roots.

According to Kaizen Bonsai, only fertilize when the plant is showing strong growth, which will very much depend on your specific type of tree. Do not try to fertilize to fix “problems”. If there are plant health issues, try other options instead, such as adjusting water schedule, pruning, loosening roots, or repotting. 

Again, how you fertilize will depend on your tree species and your very specific circumstances. To be honest, I have not given my tree any fertilizer, because it just didn’t seem to need it! It had strong steady growth, with new shoots all the time, so I have been foregoing the fertilizer.

A quick note about misting…The bonsai ficus does not necessarily need misting, but in dry environments the tree could benefit from an occasional mist. As this is a tropical plant, it does like some humidity, so an occasional mist and a wet tray can provide that little extra bit of moisture in the air.

The bonsai ficus likes to be in full sun, but this tree can tolerate indirect light as long as it gets a little bit of direct light on its leaves during the day. Southern sun is good for this plant, but less direct light from the east or west can work as well. My plants sit in a southeast window of my house, and they all seem to love it! They get a lot of direct light during the day until mid afternoon, which seems to make them happy and content. Do not leave this plant in the dark! It won’t tolerate dark corners or cold drafts (think tropical).

And don’t worry about the milky sap (latex) that will ooze out of the cuts. They are the tree’s way of creating a protective sealant to help it heal the cut.

My bonsai tree was admittedly neglected in terms of pruning, so it developed a large branch off to one side of the tree that ultimately led to the tree tipping over from the weight and being off-balance. This repotting process gave me the perfect excuse for pruning that branch, but I couldn’t bear to just throw it away. The branch was the perfect size to propagate as a new tree!

The thing to remember is that bonsai is a tree, so it’s pretty resilient when it comes to chopping off bits here and there. The tricky bit is getting the cut piece to grow roots. To prune a branch for propagation cut at a 45 degree angle, just like you would for fresh cut flowers. This helps the cutting have more of a surface to soak up much needed water.

The one bit of wiring you will want to do right away though is to wire the tree trunk into the pot when repotting. The tree will need to be anchored, and that has to be done when you repot. Wiring of the plant from the base will help stabilize the bonsai tree and create balance for the shapes you want to create and keeps the tree from toppling over. (My tree was apparently never wired into the pot, which is why it is now toppling over and in need of a triage!) The wire simply gets fed up through holes in the bottom of the pot and wound securely around the largest roots and/or tree base and then secured in a way that keeps the tree stable but does not cut into the tree itself.

Please feel free to drop a line in the comments with any of your own tips!

This article may contain a few items or commercial mentions, but I only used them for demonstration purposes only. I am not endorsing any particular product or receiving any monetary gain for this blog.