I saw this a little while ago as a better way of making toilet roll pots, I can’t lay claim to this idea so apologies to whoever did. I suppose the other way is to do nothing and just use them as pots and this is fine but if you add these steps then you’ll get better pots that stack, take up less room and don’t drop soil out of the bottom.
First fold the tube flat making sure that you make a really good crease as they’ll try to become round again if not. Then turn 90 degrees round and do the same so that you have 4 folds at even points round the tube.
Straighten it out so that it looks like this.
Now make 4 incisions along the folds at one end. It’s important that the cuts are no longer than half the short lengths, that’s the distance from one fold to another, it they’re too long then the next bits won’t work properly.
Fold them in like this, again making sure that the creases are crisp.
And open out the flaps then lay them one over the other folding the last cornet under the first so that they look like this.
Voila, square tubes that have a base and fit really neatly together. It’s a bit of a faff but I do it to all of mine now as I find that they’re really quick and work much better.