I've chosen a pot I like, but how do I stop the soil
Article written by Tom Houston, of The Northern Ireland Bonsai Society.
Bonsai pots are designed to have lots of drainage. Hence they have one or more large holes in the bottom. To keep the soil in the pot, you need to cover the hole so that the soil stays in, but water can drain out and air can get in.
The standard practice in gardening is to put broken crocks (bits of broken flower pots) or large stones in the bottom of ordinary flower pots. This won't do for bonsai because as soon as you start to move the tree around to bed it in properly and to position it just right, you'll push the crocks away from the holes. Also bonsai pots tend to be rather shallow so crocks would take up far too much room.
The answer is to cover the hole with a piece of stiff plastic mesh held in place with a 'butterfly' shaped piece of wire. In the photos which follow you might notice that I didn't use 'bonsai' mesh (That's got too many digits in the price) so I used a piece of a pot meant for pond plants; I find this does the job just fine. I prefer to use plastic mesh, but anything that doesn't rot or collapse is OK.
In the photo above, I have covered the drainage hole of a small pot with a piece of mesh. As the pot also had the hollow legs so often found in cheap pots, I have filled these with an epoxy resin such as Araldite. If I hadn't done this, there would have been a danger of water standing in these hollows and and possibly causing root rot. Another option is to drill small drainage holes at the bottom of the hollow. I prefer to fill rather than drill because it's so much easier, and a small drilled hole could easily get clogged.
How to make the 'Butterfly'
First take a length of wire. The exact length obviously depends upon the size of the hole you need to cover, but try to have too long a piece as it's easier to cut excess wire off........ Practice on a bit about six inches long to start with, that'll give you some idea of scale.
Aluminium wire is probably the best for this job, as it's usually pretty soft and thus easier to bend around the contours of the hole without the risk of chipping the pot. I'm using scrap UK household electrical copper wire here, as I've got quite a bit of it and I find it's just as good if used with care. A possible problem with copper wire is that it might corrode and discolour pale pots.
Make the first bend so that there's a nice big loop, the two straight ends cross at right angles and one is about between 3 & 4 times as long as the other.
Make the second bend so that there's another nice big loop and the two ends now point directly away from each other and are the same length. Note that both bends bring the wire back over (or under) itself. One over and one under is wrong.
Now bend the wire over where it crosses itself. Bend at right angles, the angle in this photo isn't quite right, I left it so that you can see where the wire is going.
And there we have it. (I can NEVER get the two ends the same length). The two straight ends should now be adjusted so that they are parallel and about as far apart as the width of the hole to be covered.
Then, working from inside the pot, place the mesh over the hole, pass the two straight ends of the wire down through the holes in the mesh. Make sure that they are as far apart as you can get them or the mesh will move around (try it). Finally, hold the mesh and wire in place, turn the pot upside down and bend the ends of the wire around the drainage hole so they hold the mesh firmly in place. Use your fingers to do this, not pliers, and be extremely careful not to chip the rim of the hole.
This is one of the jobs I like to do around mid-Winter to new pots or to pots that I haven't used in the previous season. It allows me to think I'm doing something useful at a time when the best thing I can do is leave the trees alone.