what to plant in September? (Zone 9 UK)

What is good to plant in a forest garden in September? (In southern England, zone 9)

So far I have planted salad burnet, lamb's lettuce and winter purslane in some new raised beds I've just built.

What else should I be planting now?

Cheers,
Paul

(An ideal answer to this question would be a link to a calendar showing what tasks need to be done in every month of the year for the first few years establishing a forest garden!)

That would be an ideal answer, but in all my searching on gardening topics, I've come up short.

Our zone 9 is a bit different than your zone 9 due to our warmer summer, but fall is brassica planting time: cabbage, kale, turnip, collard, mustard, etc. These plants germinate faster in hot weather and can put on some good growth before the cold weather slows them down. What you want to do with them for a forest garden is to get them to where you can harvest them continually through the winter. It's kind of hard to do that with a cabbage, but for all the others, you can continue to clip leaves up until they get ready to flower next spring. If you like you greens on the bitter side, you can also do the same with the various chicories.

I second mustard and kale, and any green-manure type plants you might want (I use mustard mostly as a green manure).

You can also plant some broad beans now, and autumn bulbs such as onions and garlic (and crocus, tulips or daffodils if you want those- not edible but pretty and they provide nectar earlier than most other things).