At 09:07 PM 10/18/03 -0400, Martin Haber wrote:
Pines are fussy about removing soil from their roots. If you remove all of
the soil, you'll be removing the mychoriza as well. These trees depend upon
it to grow.
So if you decide to do it, save some of the old soil to mix with the new.
In any case, wait until spring to do it.

Folks

I will respectfully disagree about the mycorrhizae part. I have never paid
much attention to it, never intentionally inoculated my pines, and I can't
seem to keep it out of them. It finds its way to them no matter the source,
whether it be imported bareroot seedlings, my own seedlings or just
repotted plants.

As for washing the roots, I am learning more all the time. I will limit
this discussion to Pinus thunbergii, since I did extensive repotting of
them this summer (usually a no no). Since my endless nursery move begin,
many of my plants have fallen into neglect and have needed emergency repotting.

The plants involved were mostly one gallon black pines that were very good
sized, heathy if a bit hungry and with no root problems. The biggest
problem was soil collapse since it had been too long since they were
repotted. I had too objectives: One was to get them into new soil so they
wouldn't have to spend the winter in soggy soil. The other was to head them
back somewhat to promote lower budbreak. Since it was midsummer, it was
excellent timing for the second objective and a terrible time for the first.

I analyzed the situation (as I constantly encourage others to do) from the
perspective of plant growth principles. Heading them back in summer was no
problem since this is an acceptable period for rapid budbreak under high
fertilizer conditions. Disturbing the roots during the heat of summer is
very dangerous since it impairs water uptake. So the repotting would have
to involve as little root disturbance as possible, but the removal of fines
was necessary. Heading the plants back at the same time would actually be
beneficial since it would reduce the transpiration load.

I decided to wash the old soil from the roots rather than try to remove it
mechanically. This seemed the best solution since washing would be much
gentler and incur less physical damage to the roots. The object was to
remove as much fine material as possible and repot into the same container
with fresh soil. No root pruning or adjustment was involved; it was deemed
too risky.

I learned a couple of things from this. A well established plant will
retain most of its root ball shape after the washing. Most of the fine
material is on TOP not the bottom of the pot. Removing the larger particles
was not easy or even necessary or desireable. Removing the finer material
from the rootball was exceedingly difficult. Finer material did NOT migrate
to the bottom of the rootball, contrary to popular belief.

This is what I did. I used a jet spray of water to remove the soil. The
upper collapsed soil was easy to remove, there were few roots in this area.
As I proceeded down the rootball, the roots became denser, and the soil was
harder to wash. I couldn't afford to spend half an hour washing out all the
soil, nor did it seem necessary. I develop a standard to limit the amount
of disturbance. As best I could, I tried not to wash so hard that the root
ball lost its integrity, although for a few plants this was impossible. I
washed the top, sides and bottom of the root ball to remove muddy material.
I continued to use a lot of water on the top of the rootball to try to
flush out the fines. This didn't work so well. It was equally proficient to
do the reverse, to flush through the bottom and let the fines drain through
the top. Once the water started coming out relatively clear with visible
specks of organic material as opposed to muddy looking dark water, I would
reverse or alter the flushing position, until it became difficult to get
any muddy water.

An interesting thing I learned is that the finer material does NOT migrate
through the rootball. In fact, it is exceedingly difficult to get it to
move at all. Frequently, I would get a clear stream from any flushing
position, then slightly jet a little deeper into the rootball with the
water: more muddy water. So, there were very few plants in which ALL the
fine material was removed, but I stopped when the rootball integrity was
threatened or about an inch deep of the rootball was clean.

In almost no cases was all or nearly all the soil removed. The coaser
material remained imbedded. Since my mix is fir bark and perlite, the
coarser perlite remained, but some still intact bark was there too. Now, if
you used a finer nursery mix, you might not be able to do this process,
since earth type soils don't have much particle integrity and will be
flushed out completely and the rootball integrity will be lost.

I repotted gently. I did not poke and probe with a chopstick or other
instrument to pack the soil, as this was deemed too destructive to the
roots. I achieved acceptable packing mostly by shaking the pot and with a
few final slams on the table to settle it.

Since these plants were already pretty hungry, I proceeded with immediate
fertilization. I have a low dose of Osmocote incorporated into my mix, and
I also gave them a full dose of granular 15-15-15 on top AFTER the initial
thorough watering flush. I took the further risk of putting them back in
full sun where they were before, although this is an overhead watered area
and sheltered by other plants and the ground stays pretty saturated, so
there is some moderation of our typically hot dry conditions.

This was a pretty risky procedure, but seemed sound. Still, I proceeded
with a bit of angst since these were very valuable cutting grown Nishiki
black pines.... AND the result is in. I checked them again yesterday. I did
about 100 pines in that batch, zero losses, stems that were cut are nicely
budded as expected with summer pruning.

Again, this was done with P. thunbergii. P. parviflora is more difficult.
If it can be done with white pine, it would probably require far more
protective aftercare. An earlier experiment with P.p. proved an abysmal
failure, probably because it was too hot and dry for them. The black pine
also had a tough time in this location, so there may a timing factor as
well. These were done in mid spring. In general, I have had far more
problems with repotting conifers in spring than in summer, but I don't have
anything conclusive to say about whether it will work under the right
conditions.

After I did this batch of one gallon plants, I got brave and repotted some
of the 2 and 3 gallon size P.t. cultivars. I got cold feet with these and
stuck them under shadecloth just to be safe for aftercare. These too all
survived, although there is not the degree of budbreak as on the one gallon
pines. This probably has too causes, one is the fact that there were done
later, and the other is that they received less light.

I again emphasize that these were HEALTHY plants despite the fact they
needed repotting. I also did a batch of P.t. mikawa pines that were not as
healthy and not growing as strongly. There were some losses in that group,
although some have budded out after completely defoliating.

I almost feel like saying "Don't try this at home". Much of what you read
and hear about bonsai horticulture is bunk. You can do more things and
perform them out of season than you usually read. HOWEVER, to accomplish
them, you have to have a good understanding of how your plants grow, a feel
for how your climate limits or enhances certain processes, and always err
on the side of caution.



Brent in Northern California
Evergreen Gardenworks USDA Zone 8 Sunset Zone 14

http://www.EvergreenGardenworks.com

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