Folks

I recently had the following exchange with a customer. I thought it might
be of general interest:

At 09:37 AM 3/1/03 -0500, Grant wrote:
Hi Brent.
New questions keep popping us as I begin to learn and practice a bit more.
This one has been nagging at me for a while and reading your article on Why
the Earth is Not Like a Pot has me thinking even more.
Here's my thought process:

I'm using the soil recipe you recommend of fir bark, perlite and peat moss.
Talk about fast draining! Pour in, out it comes. This is good. Now general
wisdom on when to water is to stick your finger in 1/2inch or
so.
But I think this is usually for a smaller bonsai pot and not for a one or
three gallon growing pot. So I stick my finger in a one gallon growing pot
1/2 inch and it would seem it always needs to be watered. But I then stick
a chop stick in and there is indeed water, just much lower in the pot.
This, I believe, is the water column you referred to created by the
impermeable layer of the pot bottom. Let's say it's the last 2 or 3 inches
from the bottom of a 12 inch pot.

It won't be that high. You are confusing a _saturated_ layer with moist
soil. They are two entirely different things. You can have a pot full of
moist soil and no saturated layer whatsoever. As water is used by the plant
or evaporates, it is wicked into the upper layers by capillary action from
the bottom of the pot. Finger action is not necessarily a good indicator,
unless you have a lot of experience. Chopstick is good. With my soils, the
mix is so light that lifting the pot is probably the best test. Often, the
pot will weigh more than twice as much after watering and immediate
drainage as opposed to critically dry.

Now, if the tree is young (or not so young) and the root ball is in
the top half of the pot, there seems to be a problem.
The roots aren't providing aeration, they're only getting water as it
passes by and I have no idea how long it's going to take them to colonize
the bottom of the pot but it doesn't seem to be super fast.

Newly repotted plants often do need watering more often, for several
reasons. One: fresh soil usually holds less water than soil that is several
months/years old, especially bonsai type soils that have an organic
element. As soils settle and begin to decompose they retain more water.
Two: Root systems in newly transplanted plants are not maximized for
absorption. This doesn't happen until new root growth finds all the pockets
of water.

As water "passes by" it doesn't leave a dry soil, it is moist even if not
saturated and moisture is available. New roots extend down into the new
soil very quickly. In winter they grow slowly, if at all, but then
transpiration losses are small also. As it warms up, the roots begin to
grow in response to temperature. Roots begin to grow quickly at bud break,
just when more water is needed. A typical rate of growth is about 1/2 to
one inch a week (elongation). So by a month or two, roots are at the bottom
of the container and quickly wicking the saturated layer.

Am I wrong in thinking this is overall not a good situation? It is
leading me to believe that somewhat shallower growing pots may be wise.

There doesn't seem to be a great deal of difference in growth relative to
container shape (same volume), that I can see anyway. Shallower pots will
retain more water because of the greater area of the saturated layer. That
can be a curse or a blessing depending on the demand for water. Aeration
also doesn't seem to vary much for plants that are not overpotted. A good
well drained mix that is watered every day or two is going to get more
aeration than is necessary for good root growth despite the container size.

Not 2 inch bonsai pot shallow but like 4 or 5 inch growing box shallow.
Am I right here? Or are there rules of thumb as to depth of pot and size of
rootball?

No, no rules guiding shape of container, see above. More importantly, is
what stage you are in, in terms of root manipulation for bonsai. It is
always easier to deal with plants in shallow pots for bonsai purposes.

My second line of questioning follows closely to the first.
I recently repotted two trees that you sent me: the one gallon Shimpaku and
the Golden Blue Atlas Cedar.
When I received them I removed minimal amounts of soil from the root ball
before potting them up in the fir bark/perlite mix.
But I was struck by the different consistencies of the soil that
encompassed the root ball and the soil now surrounding the root ball.
The soil around the ball is older and denser than new soil and I am
wondering how that effects the roots and tree. It seems to me the two
soils will absorb and hold water at different rates. Does this create a
problem?

I mentioned that above. As a soil ages, it decomposes, especially the
organic element, but even the organic to some degree, unless it is a
vitreous substance. Perlite most definitely breaks down into smaller
particles. This is not necessarily a problem, because a plant _grows_ while
it is in a container and thus demands more water. Properly designed soils
can age and retain more water about the same rate that the demand
increases. Of couse there are other factors (some article at the site
discusses all of them, maybe on soils or watering). If you prune hard, that
decreases demand, if you move it to shade that decreases demand. I think
you get the picture. The bottom line is that all the factors are relative,
in mathematical parlance, they are parameters. I can't give your fixed
numbers, because the equation has four or five parameters. Rather than
relying on rules, you have to rely on your senses and your observations. If
growth is poor, the first thing to do is to yank it out of the pot and
examine the soil, that will usually tell you what's wrong, and you have to
correct it.

Soils are designed to operate for a _range_ of conditions. As I said above,
a smaller plant in a fresh soil is not necessarily affected by lower
retention of fresh soil (but it will need to be watered more often for the
other factors stated). Established plants can tolerate a range of
conditions of higher retention because they are root colonized and have
heavy demands. But it is still a range of condtions or plants couldn't grow
at all. In general, plants respond and adapt to the conditions that exist.
I see this all the time. Unpruned plants will grow until they deplete the
water reservoir in one day. After this, growth dramatically slows down
(unless you begin watering more than once a day), because the conditions
won't support it. They survive just fine until a sudden hot day. Now the
external environment has changed and created a greater demand, and the
plant wilts where the day before it was fine. If it wilts severely, it
loses soft growth, then attaining the ability to tolerate such heat. It has
pruned itself and adapted to new conditons.

You have to see things as systems, where one change affects more than just
the obvious, it can create a whole cascade of changes in an adaptive system.

Have I created a problem similar to the dense soil and amendments
boundary you write about in the article? If so, what is the solution?

Not if you have loosened the soil so that the roots can get a hold of the
new mix and there is not a sharp boundary. In this case, I have already
prevented that by removing the pot from the juniper and loosening its roots
and breaking up the outside of the rootball. That is _why_ I do that, I
don't trust people to do it properly, so I prepare the plant for repotting,
all you have to do is add a good soil. In the case of the cedar, I believe
it was in much younger soil, so that the new soil is probably a pretty good
match, and there is not much danger of boundary effects.

Or do I just need to relax and stop being so anal.....?

You definitely need to relax, but these are good questions and show that
your thinking is leading you in the right directions. My brain does this
_constantly_, and for thousands of plants and conditions, that is why I am
so process oriented, and try to teach folks to think like this rather than
follow cookbook prescriptions. You can give a man a fish......

I'm learning, and I really want to understand what is happening and
what the repercussions for things are.

Thanks for taking the time to answer me.
Yours,
Grant L.

My pleasure

Brent


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

http://www.EvergreenGardenworks.com

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