Build instructions for a bonsai growbox

A basic instruction to create a wooden growbox for bonsai

It really is very easy to build a basic growbox for your trees. Besides some bits of wood, all you need is a few screws, and tools. With this you can build a basic growbox for bonsai yourself in under ten minutes. This manual creates a growbox of 40*40 cm (inside) and 11cm tall (inside). With slight adjustments you can of course create a larger, smaller, deeper of shallower box.
Images and design courtesy of David Roussel.

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So.. What do you need for a basic growbox?
32 screws of ~35 mm long
4 Bottom slats of 400 x 90 x 15 mm
3 Support slats of 400 x 40 x 25 mm
2 Short side slats of 400 x 150 x 15 mm
2 Long side slats of 430 x 150 x 15
Screwdriver
Carpenters square (Or a piece of A4 paper)

Put the bottom together

Take the three support slats. Lay these on the ground, parallel and evenly spaced. The outer two should be exactly so far apart that a bottom slat exactly covers them from side to side. Put the 4 bottom slats on top of these support slats, so that they form a perfect square, as in illustration 1. Use the carpenters’ square or piece of paper to make the angles perfectly square. The bottom slats should now be 1cm apart. At each intersection of support and bottom slat, insert one screw.

Add the short side panels

The short side slats are now placed on their side, against the created bottom section, on opposite sides of the bottom section. The ends are flush with the ends of the bottom section. Screw these in place to the support slats.

Add the longer side slats

The long side slats are now place on the other two opposing sides of the bottom section. Screw these to both the support slat, as well as to the short side panels.

The basic growbox is now done. When you fill this with substrate, you should use a fine mesh at the bottom to avoid the substrate falling out.

5 Comments on “Build instructions for a bonsai growbox”

  1. Hi. I have read widely about grow boxes online but still do not how early in a tree’s life one can/should put a sapling/young tree in a grow box. I have a number of 1-2 year old saplings (mostly European native deciduous trees, some conifers) which have grown in Airpots, Rootmakers, cells and 7-9inch pots and I would like to put them in grow boxes because I believe that:
    – Grow boxes promote shallow, horizontal root growth
    – Grow boxes result in faster growth as the tree roots are able to make contact with the earth through the gaps in the bottom of the grow box (the growth rate is not as fast as true ‘field growing’)
    – Growboxes are manoeuverable (but require the roots extending beneath the box to be cut)
    – Growboxes make root pruning easier as the box is lifted and the roots which extend beneath the box are cut before the remaining roots are attended to
    – Growboxes allow you to easily determine the soil substrate the tree sits in (my garden soil has a very high clay content which can become waterlogged)

    I would ‘field grow’ my saplings but judge that it is not worth trading all the advantages of grow boxes for even faster growth.

    I would really appreciate your advice as I am looking forward to building my own grow boxes.

    1. Dear Toby,

      Good to hear from you. I would say that there is one big downside to growboxes.. You need to water them. If you only have a few trees that is OK (Although.. If you go on holidays, it means that you have more trees that need watering and with the size that you can let plants grow when growing out, this may mean a lot of extra work for your caretaker.

      I think in general growing out of the main trunk goes fastest in the ground. Once the main trunk is set, move them into growboxes for the branches, closing of wounds, root refinement. In the ground you can still lift them every few years to work on the roots and avoid having too big a problem there. That being said.. I do both. I have young plants for growing out in the ground as well as trays. Although I am not sure which I prefer I see that plants in full ground do fatten up MUCH faster. 🙂

  2. Hi, GrowingBonsai. Good article on grow boxes, but I have a couple concerns. You don’t mention drilling drainage holes in the bottom or holes for wires to pass through to anchor the tree. Other than this, nice simple box design. Thank you.

    1. Hi again Jo-Anne,

      I did indeed not mention drilling holes. The bottom slats should not be flush against eachother. There should be space between them (WHich is why I mention the fine mesh on the bottom). Also, here you can attach wires or you can put screws in the boards!

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