I made something. Better still, I upcycled the festival wellies I bought for WOMAD 2010. Ta-da:

This is what they looked like when I started:

Then I drilled holes for drainage in the soles:

I just used a 6.5mm wood drill bit (the largest I had) and drilled from the outside in. I didn’t worry about the heels because they’re probably harder to drill and the water should just run down from them anyway.

I filled the wellies about two-thirds high with compost. The trick here is to make sure you do it a bit at a time and don’t leave air gaps. Make sure the compost goes right down into the toes for ballast and it’ll probably make the plants happier too. (I forgot to take a photo of this bit.)

I planted the large plants (one in each), added a bit more compost, and then planted two little plants (that you can’t really see in the photo) in front of them. You can see in the before photo that the wellies have adjustable straps on the side. I loosened these to make as much space as I could.

I fastened the two wellies together once standing using a couple of clothes pegs. This is just to make them a bit more stable.

And here is my festival welly planter with added cat:

Update 2020: The planter lasted another couple of years but had faded a lot already after just one year of weather and south-facing sunshine: