What is a bonsai growbox?
It I actually exactly what the name makes you think it is. A box to grow bonsai and/or pre-bonsai in. Normally these are constructed with a very well-draining bottom, and made to size for the tree that you are going to put in them. The depth can be adjusted to fit the height of the rootball, and the width and length to the minimal size needed to fit the longest diameter of the roots.
Images in this article have kindly been made available by Marco Buijsman
Why use a growbox?
A growbox is particularly useful when you are either planning to grow out a younger piece of stock, or if you have a collected tree with an odd-shaped rootball.
For growing out younger stock, ideally you have a flat, much wider than deep, pot. This way the roots develop mainly horizntally, aiding in the development of a wide, flat rootball. As these are not always easy to find, building a growbox is a good solution.
A growbox can be made to exactly fit the tree that you have dug. Made to the right inner dimensions. A normal pot typically is way too large for the rootball collected because, for instance, one large root requires a large diameter pot to be used. However, with bits of timber one can build a growbox for bonsai to size.
By reducing the space for the rootball, especially with weaker collected stock, you improve the wet/dry cycle of the soil. A good soil dries out fairly quick. With too much substrate in an overly large container, it is a lot harder for the plant to drain all the water, leaving it with ‘wet feet’.
As you can make these effectively from scrap timber, it is easy to make a cheap temporary container for your stock.
Drainage and air
By building these with an open bottom, you provide very good drainage, which helps with the aeration of the substrate the plant is growing in. This creates really good conditions for growth.
If you are not certain how to build a growbox, you can find one of our tutorials for building a growbox here