Rainbow Bonsai Club
Tricks and Tips

How to Make and Use a Growing Box

Making the Box

By Rick Wagner.

I used scrap wood I had lying around the car port, but of course new wood will work just fine. I used a circular saw for both ripping and cross cutting. You will need a drill bit for countersunk holes for the wood screws. I used number eight galvanized steel wood screws and a power philips bit.

You have to decide on the size and shape of your box. I needed something appropriate for planting a croton I was planning to dig from the back yard. Compute the board lengths and widths and find or purchase and cut as necessary.

I have seen and made quite a few growing boxes of different designs. I arrived at the design shown here a few years ago and continue to use it beacuse it is simple, rugged, and works well for growing bonsai.

If using multiple boards for the sides, it's important to use different widths, staggered end to side, so that the
boards will interlock with overlapping fasteners.
I put two foot boards on the bottom. These perform three functions. First, they pin the front and back boards which are
fastened by screws into the end grain of the side boards. As most woodworkers know, screws into end grain hold weakly.
Second, the feet allow air to circulate under the box and promote drainage, just as the feet on a ceramic bonsai pot do.
Third, they hold the bottom boards, to be placed inside later.
I put two handle strips on the top sides. They perform two functions: they pin the top front and back boards and
make it easier to pick up the box when it's being used.
I finished assembling the box by putting boards in the bottom, each fastened by one screw at each end.
Spar varnish inside and out will help the box last a long time. I used two coats.

Using the Box

The croton will eventually become bonsai, if it lives. The box is already approximately the size and shape of a deep rectangular bonsai pot. The twin trunk tree will eventually go into a ceramic bonsai pot about half as deep.
Andrea wanted to replace one of the crotons with a plumeria. She pruned off everything smaller than a broom handle,
and I started to dig around it on Saturday, May 25th.
The croton has been there over 50 years. Digging it up is not trivial.
Meanwhile, I prepare for putting the croton into the growing box. I wash the fines out of a bucket of sand.
Wash the sand until the water runs clear. Then put enough sand in the box to cover the bottom.

Andrea has trenched all around the croton.

I remove the croton and position it by the box.
Having spread the sand in the bottom of the box and removed much of the dirt from the roots, I position the croton in the box.
I have added compost to the box and watered it in.
Washed sand is put on the surface of the compost. This adds some rigidity to make the croton more stable.
Nine months later, the croton is doing well. Some of the longer branches have been cut earlier. February 15, 2014.

A Pair of Growing Boxes

I picked up a piece of pine wood I found curbside on the street, 3/4 inch thick, clear composite (smaller pieces bonded together, two feet wide, and six feet long, that someone had put out for refuse pickup. It was slightly damaged, but otherwise in good condition.
I built a pair of growing boxes on on Sunday, June 2nd, using the same technique as above. These boxes are a
bit smaller, 17 x 11 x 5 inches.The bottom boards fit closely, so I drilled four 3/4 inch drainage holes in the bottom of
each one using a spade bit.
Wood workers know that a spade bit through hole is not drilled through all the way from one side, but drilled nearly through
and then finished from the other side to prevent splintering. I painted the exposed end grain with some whimsical colors.
After a coat of varnish, water based this time.

After a second coat of varnish, inside and out, I covered the holes with 1/16 inch aluminum window screen, stapled to
the bottoms. The screens can be put on the inside of the box, but it's easier to staple from the bottom, and doing so
denies slugs a place to curl up and sleep.
I have had this breadfruit tree growing in the glazed pot for about a year. I'm going to transplant it into the growing
box I built.
First I mostly defoliate the breadfruit with my bonsai shears.
Then I wire four of the branches into lower positions using two pieces of aluminum bonsai wire.
I put washed coral sand into the bottom of the box. Click the image to see the full resolution version.
The finished product. I positioned the tree a bit to the left and rear of the box, filled it with potting soil, and
finished off with a layer of washed sand on top, leaving a bit of the nebari (rootage) showing.
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