When should my bonsai be re-potted?

Late winter is the best time to re-pot your bonsai tree.  Mid February is a good general average for most Bonsai trees.  During the winter, your Bonsai is dormant and the tree "rests" for the Spring.  Junipers, of course, are evergreens and don't lose their leaves like a deciduous tree, but they go dormant just the same.  During the growing season, severe root pruning and transplanting can be pretty stressful to your plant.  Ultimately, pruning your bonsai trees roots should be done just before the growing season begins because that is when your cut root ends will begin to repair themselves.  Pruning your roots too early in dormancy means the roots will be remain unhealed and open, and therefor susceptible to root rot and diseases.

Why should I re-pot my bonsai?

A Bonsai tree lives in a very small world. Its entire earth is bound by the dimensions of a small bonsai pot can become root-bound pretty quickly.  As a Bonsai tree grows, the root system takes the place of what used to be soil.  (That's right, it "used" it).  A bonsai cannot thrive if it doesn't have a proportionate amount of soil.  As new roots are produced, older roots become ineffective and should be pruned off.

Bonsai soil is course by design to increase drainage.  That leaves behind a lot of built up not-so-great stuff in the soil.  A build up of salts and minerals is common too.  Replacing the soil is a quick way to fix a bonsai plant's balance of pH and built up salts and chemicals.


Article you might like - An Introduction To Bonsai Soil


How often should I re-pot my bonsai?

Generally, once a year for younger Bonsai trees and up to every three years for older ones.  You won't really know until you look at the roots, but most bonsai trees are re-potted every February.  They can be potted again if needed during the growing season.

If you can take the tree out of its pot and the root ball comes out in one piece, then it 'it's time to re-pot it.

Should I put my bonsai in a bigger pot?

Not necessarily.  Re-potting doesn't mean replace the pot, it really should be thought of as replacing the soil.  Although most Bonsai trees and certainly Junipers will get bigger every year and a bigger pot will do it a lot of good, not only for the health of the plant but aesthetically too.

Won't cutting the roots of a plant kill it?

Yeah, pretty much...(not expecting that were you?)  But pruning and combing the roots of a Bonsai doesn't mean cutting off the roots.  The purpose is to prune out the ineffective old ones and the new ones if they've become too long.  A root system moves water and nutrients up to the top of the tree through a process called transpiration.  Kind of like photosynthesis in reverse.  Nearly all of the water that is absorbed by a root system is taken in through the tiny root hairs at the tips of the roots.  The big fat roots are generally useless and can be cut away.  A Bonsai tree has to be balanced between the roots that support the tree and photosynthesis.  Small amounts of foliage, like a lot of bonsai trees are designed to have, means less photosynthesis that can support the roots.  Therefore, you need less roots and vice versa.

What kind of soil do I need to use?

Use a potting medium specifically blended for bonsai.  They are well worth the money.  They are balanced and mixed to make sure that your bonsai is well drained.  Get one that has been "double sifted" which means the big chunks of stuff have been sifted out and the very small particles too.  The dust from peat moss for example can choke out tender new root growth.  

Tips on Repotting:

- Re-pot your bonsai out of the sun; exposed roots will dry out very quickly in the sun or wind.  I always keep a water bottle handy to mist the roots as I work.

- Carefully comb out the roots to loosen them up.  Trim the lanky, long newer roots.  Active roots are the small white ones that are on the periphery of the root ball.  Any roots that are a little larger and do not have smaller white roots at the end of them can be cut off.  Don't completely eliminate the old soil from the root system.  Biologically, it's good to take some of the bacteria, enzymes, pH level, etc. that the tree knows from the old soil, to the new soil.

- Once you have completed the root pruning, put a layer of gravel or mulch on the bottom of the pot.  Put a shallow layer of soil down next so the roots are not place directly on the gravel.  (Gravel can get pretty hot in just a few minutes of sun too).  Spread the roots up and out to the side when placing the tree in the pot.

- This is the point you might want to spend a little time looking at the placement of the Bonsai in the pot.  Remember to plant non symmetrical trees off center and make sure the best side is facing the right way in the pot.

- Once the tree is where you want it, gently fill in the pot with soil.  Press it down well with your fingers so that the soil fills in the spaces in the roots.  Then place the whole pot in a pan of water of a sink for a half hour or so.  This allows the soil be be evenly and completely moistened.  Don't press the soil down again, you want it to be a little loose, but you should place more soil in areas where there are depressions.

- Decorate with gravel or sand.  This helps keep the moisture level on the soil surface up.

- Put on a jazz CD, have a little wine and enjoy.


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