Do they have to be in pots, Ben? I grow all of them in the ground here in the soggy UK and don't need to worry about water, either too much or too little.

But if you do need to grow them in containers, perlite is a good amendment to choose. Be sure to add plenty; a little bit won't accomplish what you need it to.

Yeah I think we get even more rain here in Auckland over winter (I'm from the UK originally), but dry summers. Sadly I have to grow them in pots for now due to space issues.

Would 20% perlite be a good proportion?

Cheers,

Ben

we have a lot of rain and cold springs here in Maine. that combo can be deadly for some plants. I've added perlite or pea gravel 20 to 30% is about right. also i put some 1/2in . river pebbles in a 1in. layer in the bottom of the pot. helps it drain even better. good luck!

The Mint doesn't really fit in the same group as Rosemary, Sage and Oregano. The latter are native to Mediterranean habitats. Mint hails from damp waterside areas and needs a moister environment.

BTW the pebbles in the bottom of the pot technique, although traditional practice, is now discredited. It does nothing for the drainage. I've never used perlite but if you can get horticultural grit that can be added to the mix in containers.

don't know who discredited it but my grandfather used to do it and its worked for me. more air gaps lets water drain easier. its common sense.

While one may reasonably think adding rocks, pebbles or pot shards to the bottom of a container may improve drainage, it does not. In fact, it impedes proper drainage. Water moving through a container efficiently needs to encounter uniform soil structure. When you change that soil structure uniformity - like by adding so-called 'drainage enhancers' to the bottom of the container - water naturally slows and this can create drainage issues. These materials also serve to raise the perched water table or that area at the bottom of the container mix that remains consistently damp or even wet. This too can create drainage issues.

This is not speculation but well-established soil science. Water movement is determined by physics. There is an excellent and extremity long running thread in the Container Gardening forum that discusses this at length - Water Movement and Retention. It should be required reading for anyone that grows anything in containers :-))