Generally, do what comes naturally. There are a fair number of
woodland plants, but many are thugs; if you have ramsons or
bluebells, you won't have much else. You need to check what the
soil is, how dense the shade is, and how much water gets there.
Basically, go for woodland bulbs and similar herbaceous plants,
perhaps some woodland shrubs (I recommend Danae racemosa, if you
can get it) and possibly the odd climber.

Your strategy of watching for a year is quite right, though you
might want to plant some bulbs in August or early September if
they seem appropriate.


Regards,
Nick Maclaren.