Juniper re-potting.

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Despite their popularity, I find myself in the position of doing my first re-potting on a Juniper this Spring. I am comfortable working on deciduous material but would like a few pointers on this subject.

I acquired this tree last year in late Spring/early Summer for a styling contest on another forum. The bottom of the root-ball was reduced by about one third (sawn off) but otherwise was not disturbed. The tree was fine all last summer and has spent the Fall and Winter out of its pot and planted in my growing bed, well mulched and, finally, under some snow cover.

I recently prepared a batch of soil/medium for this tree that consists of roughly half lava, half Haydite and a little charcoal as well. This is my first excursion into the realm of 100% in-organic (excepting the charcoal) mix. Below is a picture to get the idea of the scale of this mix, it is a little coarser than my usual mix, does this seem appropriate? What is the approximate time frame for this type of work? I assume that it is acceptable/preferable to totally remove the old potting mix. And finally, how aggressive can I be WRT my root pruning? Advice on anything else I am overlooking will be appreciated as well, thanks.

Norm
 

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Norm, that soil mix seems a bit coarse, if that is a quarter. I have never used soil that coarse even for alpine trees. Boon uses as his coarse mix, particles about half that size. You are on the right track as to soil makeup, but this is going to require you to water at least three times a day. In fact, Boon waters three times a day and uses the smaller mix.

What variety is the juniper? A procumbens is probably going to want particle size in the 1/4 to 3/8 inch size.

Remember when you repot this tree that you need to get all the old soil from the roots without bare-rooting the tree;) . There is a very easy way to do this that does not slow down growth of the tree at all. Just tease out the tips on one side, bare-root the other and prune the roots to balance growth. Next repotting reverse sides. In two repottings you have rid yourself of pesky bad soil and your tree is ready to grow well.

Good luck!
 

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Chris,

Thanks for the helpful response. This Juniper is not a traditional bonsai variety; it is “Old Gold” a scale type Juniper used in the landscape trade. After purchasing it I learned that it has fallen out of favor among nurserymen and is not a considered a particularly strong grower, although it seems healthy enough.

My local source for Haydite has discontinued it and I pretty much cleaned him out. This provided me with about 7 gallons of this larger material that I had hoped to utilize somehow, but if it is too large then I guess it will go to waste.

Below are a few pictures, one of the foliage and another showing an alternative to the previous mix. The components shown above are considerably smaller than the previous mix and just a bit coarser than the mix I have been using on my deciduous trees. I have provided a sample of the previous mix, below, to aid in comparison. Does this seem more appropriate?

Realistically, I have no hope of watering three times a day. My other material does well with my checking it once a day, but I use a bark component with them. This leads me to another question, if you don’t mind. What factors in more regarding watering frequency, the presence or absence of a bark/organic component or the particle sizes, irrespective of their composition? And finally, do you suggest that I use bark with Junipers?

Norm
 

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I avoid organic matter entirely, except for the bit of charcoal you mentioned. Organic components rot, which robs the tree of needed nitrogen. They collapse over time, which leaves air pockets in the roots. And they do not allow as precise regulation of fertilization because they absorb some nutrient and release it later when we don't want it.

It looks like the soil in the upper left is pretty close to what I would use, the upper right is not too bad either. The one thing I think you may need is akadama or something like it. Unless your haydite and lava are quite porous...

Generally with soilless mixes, particle size has a strong effect on water retention. I use large particles on alpine trees (scots pine, white pine if I had one, etc.) that need less water, and the same mix but small particles on water-loving trees like JBP, etc. Add extra akadama for deciduous trees.
 

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Chris,

It looks like the soil in the upper left is pretty close to what I would use, the upper right is not too bad either. The one thing I think you may need is akadama or something like it. Unless your haydite and lava are quite porous...
The material in the upper left position is Haydite, not terribly porous, at least not visibly so. Upper right is the lava, this is much more porous. These are the same components as the original mix shown, only smaller and not yet combined. I have not yet made the leap to imported soil components so I think I will go with this (smaller size) mix and forgo the bark entirely, as was my original intention. Thanks again for your help.

Norm
 

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