Most bonsai will need to be repotted several times during their lifespan. This is because they are long-living plants, and they benefit from having their roots cleaned, and having access to fresh, nutrient-rich bonsai soil.
How often to report a bonsai
The general rule is, the smaller the pot the more frequently it will need to be repotted. There is no hard and fast rule about how often you should repot bonsai. Small bonsai may benefit from repotting every 2- 3 years, while larger plants could go 4-5 years before needing to be repotted. You will know that a plant needs to be repotted when the pot feels heavier than it once did and you can feel root growth in all areas of the soil. Repotting is also a good idea if your plant has root damage, has been allowed to become very dry or has been infected with fungus or bacteria.
When to report a bonsai
Both indoor and outdoor bonsai are best repotted in late winter or early spring, before the plant really takes off with new growth. You don’t want to expose the plant to extreme temperatures during the repotting process. If your plant is an indoor plant, it is preferable to set up a repotting station in the same environment rather than taking it out into very hot weather. However, a little exposure to mild spring weather won’t hurt it. If you have multiple types of bonsai, begin the repotting cycle with the evergreens including the boxwoods, junipers and azalea. Next, do the deciduous plants in your collection, waiting until you see some swelling and budding before you commencing. Remove any dead leaves at this time.
Check the health of the bonsai roots
Remove the bonsai plant by wiggling it free from its pot, beginning at the edges. Take it out from the pot entirely. It is a good idea to use the opportunity of repotting to examine your bonsai’s root system and remove any that have died or which appear rotten. Dead roots will be brownish in color, while rotten ones will be mushy or slimy, and may have a rotten aroma. Use bonsai scissors to remove any roots which are unhealthy.
Trimming bonsai roots
While you are holding the plant, loosen off any dirt caught between the roots and where possible, using a chopstick or some other implement that allows you to poke and wiggle between the roots. Only use your fingers to untangle roots that have become messy. Trimming healthy roots back can also encourage new growth, so give the ends a short trim. Don’t remove more than one third of the total root mass. Don’t be alarmed if some clumps of roots fall off as you are doing this. They typically have detached from the plant some time ago.
Preparing the new soil
Providing your bonsai with new soil will give it a boost. It is important to use a high-quality soil that has all of the elements your plant needs. Take care in selecting a blend of organic and mineral matter. This mixture needs to provide both water retention and create small pockets where air can circulate. Popular mineral elements include coarse sand, pumice, gravel or loam. Good choices for the organic material are pine bark, peat moss or compost soil.
Preparing the container
If you want to return your bonsai to its existing container, you will need to make sure you give it a good wash with disinfectant or bleach to remove any bacteria or fungus. Let the pot dry in the sunshine before you line the bottom with the mineral part of your mix. If you want to upgrade and move to a bigger container, it doesn’t hurt to wash it out as well. And of course, ensure that it has the draining holes that your plant will require. As you move to a bigger pot, you will encourage and enable more plant growth to occur. If you are happy with the size of the plant and want to keep the plant the same size it is, opt for using the same container or another of the same size and volume.
Once you have selected and cleaned your container, and trimmed and cleaned your plant, it’s time to repot it. Ensure there is a base layer of sandy material in the pot then place the plant inside, spreading the roots out as far as possible. Keep the roots moist during this process by spraying as you go. Then, build up around the plant with your organic and mineral material.
• Work gently to get your bonsai into the desired position in the pot
• Don’t press too firmly on the soil or you may eliminate air pockets which are useful for the plant
• Ensure soil mix is pushed to all corners of the pot evenly, as well as in between the root system
• Take the soil to the top of the container, leaving the top part of the root system a little exposed
• Give your plant a big drink of water once repotted, using either top watering or immersion method
• Once you have finished watering, ensure that good draining is occurring
• Use colored gravel, moss or other decorative elements around the base to make your bonsai unique
Tools for repotting your bonsai
Although you can use common gardening and pruning scissors, there are a number of tools that have been designed specifically to help with the repotting and pruning of bonsai. These include:
• Bonsai root hooks – for untangling roots
• Bonsai tweezers – for grabbing and manipulating roots
• Bonsai spatula – for dealing with dirt
• Bonsai repotting sickle/ knife – for removing unnecessary roots
• Bonsai trimming shears – for removing shoots
These tools often come with wooden handles and stainless steel elements to help you dig and cut very cleanly.
The bottom line: you will become more comfortable with the act of repotting your bonsai the more often you do it. Your bonsai will benefit from a good tidy up, clean soil and a beautiful new container or pot.