When to repot and root pruning question.

David M. Martin

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Some of you can look at a picture of a tree and tell someone that they need to repot. I however can't do that. Is there a basic rule of thumb for repotting?

Secondly, when I repotted last Spring, I trimmed the hardened, (is lignated the correct term?), roots above the soil line which defined the trunk of my Rock Juniper beautifully. I combed the root ball and found that the remaining hair roots were very long. I did not trim the hair roots and I'm wondering if I should have shortened them to some degree. Should the hair roots be shortened and if so, is there a standard for that process one should go by?
 

rockm

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One of the tell-tale signs that a tree needs a repot is how quickly water drains off the surface. Water should drain very quickly THROUGH the top of the soil in a second or two. If it ponds, or drains s-l-o-w-l-y, then you can bet the soil is compacted and/or the root mass is so thick it is impeding water flow.

As for cutting feeder (hairy) roots, you can, and must trim some at repotting. Exactly how much depends on species, health etc. It's best to be on the cautious side with conifers, but more aggressive with deciduous species.
 

Vance Wood

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I combed the root ball and found that the remaining hair roots were very long. I did not trim the hair roots and I'm wondering if I should have shortened them to some degree. Should the hair roots be shortened and if so, is there a standard for that process one should go by?

The rule of thumb is to cut these roots by 1/3. You have to shorten these roots in bonsai in order to promote back growth and the continuation of fine roots. The roots you do not cut will eventually become lignified and useless. You did right in eleminating the heavy roots, in nature they only anchor the tree in the ground. In bonsai we eliminate the heavy roots except those on the surface that are there as a design feature, the rest of the root system should be made up of fine roots. A lot of fine roots will do the same job a few larger roots will do in holding the tree in the pot while prodiving the resources a tree needs in a limited amount of space. Root pruning is crucial in bonsai; the trick is not to take too much or take the wrong ones. The only way you can learn this is by doing it.
 

Umeboshi

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There are a couple of other signs that you can look for to know when a tree needs a repot. One is if the soil and tree is bulging upwards from the pot and another is if there are many roots escaping through the drainage holes. Both can indicate that the tree should be repotted.
 

Vance Wood

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There are a few guidelines that can be followed. Tropicals and deciduous trees should be re-potted every two or three years, some growers re-pot their Ficus bonsai at least once a year, and some in areas with prolonged growing seasons, twice a year. Conifers should be re-potted every three to five years unless you are dealing with very old trees which can be pushed to as many as ten.

How important is re-potting? It depends on the tree. In my experience the one tree with the most critical re-potting demands is the Procumbens Juniper. Most Junipers can tolerate going a year or two beyond the recommended three years but a Procumbens will start to look bad and fail soon after. In my experience once they become root bound you MUST do something and quickly.

The time to repot is largely species dependant. For this you might have to do some hunting around and asking questions of people who have these trees. Most trees respond best to a spring repotting but not all of them. Some do better with summer repotting and others with fall repotting. I would recomend you making out a chart bassed on people's experience and sucesses.
 
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