Inappropriate Soil!

     We’ve all heard warnings about using the wrong sort of soil for a bonsai. Sitting on my benches right now are some examples of what can happen when that is done.

In December 2011 I bought a baker’s dozen of young ponderosa pines; they were probably 3 years old, all in 1-gallon nursery pots. I described the trees, and the purpose I had in mind for them, in this post.

When I bought them, the pines were potted in what is probably the producer’s standard mix: sand with some organics blended in. That mix is economical, I’m sure, and it’s OK as a general-purpose blend, especially when the plant is expected to grow in it for only a short while before going into the ground. Some species, such as bald cypress, would grow well in it indefinitely. But Pinus ponderosa is a dryland pine. To quote Andy Smith, forester and bonsai professional: “Ponderosa roots are much better at getting the last molecule of water out of dry soil, than they are at getting oxygen out of soggy soil.” 

Needles browning from the tips back: typical of a chronically over-watered pine.

That mix was too fine-textured (and thus too poorly drained) for ponderosa pines to sit in for very long; and when I bought these trees, they had already been in that soil for more than 20 months! To make matters worse, all the plants in the garden center were being watered on the same schedule – the pines as often as the maples and azaleas.

The mix was staying too wet for the ponderosas. The result was that their roots were slowly suffocating. The symptoms showed up in the needles: large numbers of them began to brown, starting at the tips. When I got the trees, most of them showed this tell-tale sign; some more, some less, but they were almost all affected.

A few new needles were produced, at the ends of the candles.

Early in April 2012 -- as soon as buds began to swell -- I started repotting them into a coarser, better-draining mix: approximately 70% Turface and 30% organics, with no particles less than 1 mm across. The first picture was taken just before one of these trees was repotted. The dead needles are very evident.

I’ve kept these trees in partial shade over the summer because many were (and still are) weak, and I’ve been very careful to let the soil dry somewhat between waterings. One has died anyway, too far gone to recover. Of the rest, the tree shown above has the farthest to go. Here’s another picture of it, taken two days ago. (Yes, the same one; when I repotted, I leveled each tree’s nebari.)

But I am optimistic for it. This ponderosa, like several others, produced only a few new needles this spring, at the end of its candles. But those needles are healthy, and with the green that remains on some older needles, I hope the tree will be able to photosynthesize enough to build its reserves for next spring. Some twigs will be lost, I’m sure. But I believe there’s a good chance the tree itself will pull thru.

And this tree, in these pictures, is the weakest of the survivors.The rest are in better shape.

Closer look at this year's needles, and the green remaining on some older ones.

A rather dramatic demonstration, I think, of the need for appropriate soil!

:-0  :-0  :-0