What shouldn't go in your compost bin?

If you get your pile hot enough you can put anything organic in. In reality it's hard to get the pile consistently hot enough all the way through and turning regularly can be a lot of effort. I don't put seed heads in, or any roots of persistent weeds (only the foliage). Stuff like ground elder I would drown or solarise instead, but our green bin collection is free so it goes in there for the professional composters to take care of.

You can bash avocado stones into bits with a brick etc. to make them break down quicker. The skins I find even tougher to compost than the stones!

£50 for a Green Johanna is a great price!