Best way to start

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I'm starting a wilding project at the bottom of my garden. It's a sml area screened with cob nut trees, privet hedge,elder tree,silver birch,five aronias which are well grown,mahonia, Myrtle, strawberry tree, rosemary,sage, lupins,Solomon's seal,various bulbs,forget me not etc. The rest is grass apart from some honeysuckles, barberry,mint,fruit bushes and various flowering shrubs. What's the best flowers for a sheltered part shade but mostly sunny spot,to plant in pockets in existing grass,to spread asit wishes. Any advice appreciated.