Trick question! The answer seems to be that you can't.

I had seen no action out of a large Dryopteris wallichiana this year and figured it had bitten the dust. It's several years old but is in a sort of poor spot, close to the base of a big mock orange and within the root zone of a big willow. So I thought maybe it just got robbed of moisture in early spring. But no! Here we are in LATE AUGUST and I just noticed that the thing has a frond unfurling. Unbelievable. If this had been in a pot I would have ditched it a long time ago.

So the motto is: never give up.

KarinL