How do you repot trees with a solid root ball?

[justBonsai]

A lot of times when I work on some pre-bonsai or raw material its been growing in the same pot most if not all of its life. The result is an extremely dense compacted root ball that cannot be broken apart. On some deciduous trees I can simply cut off the entire mass and regrow a new root system but my less vigorous or coniferous trees cannot handle the stress.

How should I go about repotting these trees so that I can compact the root ball and introduce new soil in the center of the root mass? What I thought to do is to slice out sections, like a pie every growing season until I remove the entire old root mass?

Julian

 

[milehigh_7]

It's for this very purpose that Vance invented the screen side pot. There once was a great article he wrote on this very subject. Maybe someone knows how to find the information.

 

[milehigh_7]

Found it:

http://ofbonsai.org/techniques/pruning-trimming-and-pinching/root-pruning-and-why-part-two

 

[justBonsai]

I read the article but I didn't understand it too well. Where in that article does it discuss what to do with the old root mass? The tree in question is a small coast live oak I've been developing for a year in a half. These native oaks develop insanely fast here and branch structure is progressing well. The issue is that I don't think it was ever repotted in its old nursery can. During my initial repotting I did bare-root and jet wash out as much of the old soil as possible but the very core is still intact.

Because I eventually like to cram my tree in a tiny pot I need the soil directly under the tree to be my bonsai soil where I can build a dense high quality root system.

**
I think you may have linked the wrong article. This one talk about building the new root system but the last one talked about root grafting:
http://ofbonsai.org/techniques/pruning-trimming-and-pinching/root-pruning-and-why

 

[sorce]

So you have washed off the ball....

But all still be cutting blind into some stuff?

When I repotted my mugo...
I didn't cut out pie slices,
Just made one blind cut in and raked it out a bit.

I reckon you could do that.

Just take good pictures or Mark the area you did well if you do anything....so you remember where it was...

But I would ask one of them fellers been rocking oaks.

@Zach Smith ?

@rockm ?

Sorce

 

[petegreg]

You can use chopsticks + water jet to get rid of old soil in the core below the trunk.

With azaleas...very solid root ball... I simply cut wedges into root ball (triangle cuts), then remove cut off roots carefully and fill it with new soil, that's it.

 

[Dav4]

On big, dense root balls, I almost always start by sawing a portion off the root ball off the bottom. If I'm certain most of the roots are leaving the trunk up near the top, I saw off a lot, maybe 50-60%. If I'm not sure, I'll saw off less. Once the bottom is cut, I'll use chop sticks and a hose to work the soil away from the root mass on the top, bottom, and sides and reduce as needed with the goal of eventually getting it into a decent training pot, though many times it goes back into a nursery can for a season or two. Obviously, if it's a conifer, I'm not bare rooting, but just reducing the roots. With a maple, I'm ruthless and remove all the old soil and most of the roots. Having never worked live oak, I really can't give you specific advice other then to say that you need to eventually lose that core of old soil, and I suppose you can do it at the next re-pot?

 

[rockm]

With oak, you can be fairly aggressive. Simply sawing off the bottom half of the compacted root mass can free things up considerably. After that, use your fingers to work out where the remaining roots are, using an OCCASIONAL blast of water with a hose. Don't blast away at the roots with the hose--you want some soil to remain. With this, You can pick though and find the big dominant roots and shorten them further. Pay particular attention to the part directly underneath the trunk. I tend to reach into the roots as far as possible and remove the roots growing directly down from the trunk, which forces the roots to spread laterally.

FWIW, I've never had any significant success with the "pie wedge" approach with deciduous trees. I've found it' better to just saw off the bottom of the root mass and go from there. It's a more even way to do things and does more to untangle the mass over time.

 

[Paradox]

I agree with Dav4 and rockm.

Understand that you are most likely not going from a nursery can to a bonsai pot in one step. It usually takes more than one and most of the time 2 or more steps depending on the tree.

 

[Zach Smith]

With a new pre-bonsai that's in a standard deep nursery pot, I always saw off most of the root mass (once I've verified where the good surface roots are, don't want to cut off too much on the first pass) and then reduce around the perimeter using an old pair of shears, then use a root hook to untangle the bad actors, then do a final trim to fit, then finally wash off what's left to remove the non-bonsai soil. When repotting a bonsai, most of the time it's just pruning around the perimeter and on the bottom to allow room for new roots to grow. I've used the pie-wedge approach on occasion and it works all right. It's not always necessary, though, especially if you repot fairly frequently.

Zach

 

[milehigh_7]

The tree in question is a small coast live oak I've been developing for a year in a half.

What the others are recommending for your oak is what I have done with oaks.

http://www.bonsainut.com/threads/quercus-virginiana.4751/page-2#post-137751

 

[justBonsai]

Thanks for the advice everyone. In my initial repotting I did saw off the bottom half of the root ball and worked the sides. There was just no way I could completely untangle the center mass without seriously stressing the tree--it was just too compacted to comb out. Since I already did the first cut back and major root reduction last year I probably will give the tree another growing season before doing a second round.

 

[milehigh_7]

Thanks for the advice everyone. In my initial repotting I did saw off the bottom half of the root ball and worked the sides. There was just no way I could completely untangle the center mass without seriously stressing the tree--it was just too compacted to comb out. Since I already did the first cut back and major root reduction last year I probably will give the tree another growing season before doing a second round.

It's often a several year job so don't rush.

 

[bonsaibp]

Those trees are often difficult to repot. First off I'd be prepared for it to take a couple of years at least. What I've done is use the method advised by Boon and do a half bareroot. Not an easy task but well worth it. There are plenty of references to how to do this. He usually waits two years between doing the halves but I find that here with oaks one year is usually enough. After that it's just a regular repotting.