Call it "Validation of Concept."

     In April 2010 I bought a yamadori ponderosa pine (Pinus ponderosa) from Andy Smith of Golden Arrow Bonsai. It also seemed like a good idea, a few months later, to buy a small nursery-grown ponderosa pine for a few dollars as a "learning tree." I had lost my first yamadori ponderosa through a series of mistakes of ignorance, and preferred, if possible, to make any further learning mistakes on a tree I could better afford to lose.

To develop a shallow, compact rootpad on the "learning tree," I moved it into a homemade training box in the spring of 2011. Because Pinus ponderosa is native to a fairly dry climate, I decided to take a chance and use 1/8-inch-mesh hardware cloth for the entire floor of the box. (For any who don't know, "hardware cloth" is a galvanized steel mesh - think of it as window screen on steroids.) The purpose was to promote air-pruning: roots that grew downward and out through the mesh would dry out at the tips once in the open air, and the tips would die. The roots would seal off the dead tips, thereby blocking out pathogens and preventing moisture loss; and would branch further back along their length, within the soil mass.

Here's a picture of the box before use:

The interior dimensions of the box were 10 inches by 12-1/2 inches by 3-1/2 inches
(25-1/2 cm by 30-1/2 cm by almost 9 cm).

Also because ponderosa is a dryland pine, I used a coarse mix, with a low percentage of organic material and particles more than 3 mm across. The mix drained so well, in fact, that I was always a little extra-careful to water this tree adequately. Here's the tree in the box about a year later, after some pruning:

The lower trunk was about as thick as my thumb. April 29, 2012.

I'm embarrassed to admit that I left the tree un-repotted for six years (to the day, by the way.) (Six years - fifty lashes with a wet noodle!) By this spring it was clearly high time to repot. I did the job this past weekend.

And the rootpad turned out be everything I could have hoped for! It had filled the box in those six years, but was only about 2-1/2 inches thick (almost 6-1/2 cm,) and quite compact. I'll let the next pictures tell you more:

Rootpad filling the box. April 8, 2017

The rootpad freed. A nebari had begun to develop as well.

The rootpad cleaned up.

You can see that the rootpad, besides being compact, is dense, with plenty of small roots ready to throw out more feeders. If the above-ground part of the tree hadn't needed more development, I could have moved this pine straight into a bonsai pot! I think I can safely say that the full mesh bottom in the training box proved its worth.

I do want the upper part of this tree to grow a good deal more before I start serious training of the branches, so I moved it into a growing pot with more room for the roots. I know I'll lose some of the compactness of the root system, but I'll just have to re-develop that later.

This picture is taken from about the same angle as the two immediately above.

The box is rather dilapidated - even pressure-treated wood succumbs to moisture eventually. I doubt it would stand up to holding another tree for even a couple of years.  But it served its purpose well! 👍

:-)  :-)  :-)

Dog Dishes As Training Pots

(With apologies to Snoopy.)

     I'm like most bonsaiists who work with a limited budget, I think: I'm always on the lookout for new ideas for inexpensive training pots. A year or so ago I found another kind of container that fills the bill quite nicely: rigid plastic dog dishes.

The dishes I found at a major chain discount store are round, 9 inches (almost 23 cm) in internal diameter and just over 3 inches (7-1/2 cm) deep; a perfect size for many small-to-medium bonsai-in-training. I got them for around $10 apiece, and they'll last thru years of repeated use.

The dark material in the center is glue from the label; I couldn't get all of it off.

The plastic is not as rigid as metal, but it is rigid enough to not flex with ordinary handling. For any who don't know, that's important because if the walls of a container flex very much, the soil inside flexes and shifts. When the soil flexes, the roots are flexed as well. And - here's the reason it matters - roots, unlike branches, aren't made to take much bending. Finer, not-yet-lignified roots in particular - including the all-important feeder roots - break easily with any motion of the soil.

(I used to use flexible plastic containers, such as dishpans and oil drain pans, as growing and training containers because they're inexpensive. At a workshop with Kathy Shaner in 2006, I realized that a training container with flexible walls and bottom is not a good idea, and why it's not. No more plastic dishpans!)

A homeowner's cordless drill works fine for creating the holes. I used a 3/32-inch bit for the small holes, and a 1-inch wood bit for the drain holes.

(Yes, I need to clean the rust off the bit. It still did its job.)

Three 1-inch drainage holes should be fine.

The small holes in clusters of three, running around the circumference of the pot roughly an inch below the rim, are there to encourage air-pruning. Any small root that grows into one of those holes will emerge into the open air, and its tip will dry out and die. The rootlet will respond in two ways: it will seal off the dead tip, which will keep out pathogens; and it will branch further back along its length, within the soil. The more that happens, the more of a compact root system the tree will have.

Its marks don't show in the picture, but I also used a rotating wire brush to rough up the inner surface of the walls. A rougher surface will both give the roots something more to grip, and encourage them to branch a little more.

Inexpensive stick-on plastic "bumpers" do a very adequate job as feet, to keep too much water from collecting under the pot. They cost under $3 at a local DIY store.

You can also see the holes for tie-in wires, which don't show up well in the previous picture.

I leave you with a picture of this training container with its new (as of yesterday) occupant: a shohin-sized yew bonsai-in-training!

Taxus x media 'Densiformis'. After two years in this container, it should ready for a permanent pot.

:-)  :-)  :-)