We spend a lot of time talking with many new bonsai enthusiasts. Every time the topic of repotting comes up, we inevitably hear the following two questions (usually in quick succession): "How do I repot my bonsai?" and "When should I repot my bonsai?"
It can be an intimating thought. The vague answer is that it depends on the type of plant and the particular growing location. In general, it is best to repot right before your bonsai begins growing vigorously. In most cases this is spring.
However, there are exceptions to every rule, so you should consult an expert to really determine what the best repotting season is for your particular bonsai.
How often should I repot?
You need to consider a number of different factors. As the top of your tree grows, so do the roots. All bonsai need to be repotted (and root pruned) to maintain good health. For the roots, trimming gives them room to grow. At the same time, this is a good chance to replace old, worn out bonsai soil.
Some other factors to consider:
Some plant species are more prolific root producers than others. Others can go years between repotting.
Young trees or trees in small bonsai pots need more frequent root pruning.
Plants in very shallow pots do not have very much depth for roots to expand.
Some tropical trees that experience a year-round growing season can fill up the pot with roots very quickly.
What do I need?
So, it's time to repot. Here are a few pointers to get you going.
A new pot. If you are not using the same pot, you will need a suitable pot, usually an inch or bigger on all sides.
Bonsai soil. Bonsai soil - not regular potting soil - is essential because regular potting soil is too dense. Also, be sure to use a premixed bonsai soil, or if you are mixing your own, make sure you get some professional advice on the right components.
Basic tools. You will also need some basic tools for the repotting process:
A root rake or root hook for combing out the roots.
Pruning shears for cutting the roots.
A mesh or screen to cover the holes of the pot.
That's it! Now you're ready to start the repotting process!
How do I repot my tree?
First, relax and take a deep breath. You're going to be fine, trust us.
Good. Now that you're ready, start by lifting the tree out of its pot. The root mass will probably have assumed the contours of your pot; if so, you will probably see a heavy mat of roots on the bottom of the root ball.
Then, with your root hook, gently loosen and comb out the bottom third of the root ball.
With a sharp pair of pruning shears, cut off combed off this bottom third of the root ball.
Be sure to cut and shorten the large heavy roots. Remember, a bonsai's most important roots are the small, fine feeder roots.
Now prepare your bonsai pot with mesh or screen covering the drainage holes. Sprinkle a fresh layer of soil in the bottom of the pot, with a mound of soil right in the middle.
Place the tree in its original position (or the best position possible), taking care to spread the roots out evenly.
Add more soil and work it in among the roots with your root hook. Make sure that all the soil settles in and that there are no air pockets.
Then, soak the tree in its pot using the immersion method. (For more watering tips, please refer to our Watering Tips articles.)
After the repotting process, let the tree recover for a couple of weeks out of full sun and wind. Do not fertilize until new growth starts to emerge. Water only to keep the entire root/soil mass moist - not soggy.
And, you're done! Now that wasn't so hard, was it?
Associated tools for repotting:
Root hook or a root rake
Fertilizer. Fertilizer is one of the most important maintenance supplies you will need. There are many different types of fertilizer to choose from, so educate yourself to make sure you pick the one that is right for your bonsai. Popular choices include organic fertilizers or liquid fertilizer with a fish/seaweed base.
Extra bonsai soil. Remember, you will probably have to replace soil that washes away, so it's a good idea to have extra soil on hand. It is best to use a soil that is similar to the one your bonsai is already potted in.
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