Removing the dead leaves etc is the right thing to do, I'm sure and hopefully, new growth will appear but this may take some time.
With good care they should thrive in pots for 20 + years.
For best results re-pot every 2 years.
Add slow release fertilizer granules to general purpose compost.
Give a liquid feed every 2 weeks from mid spring to late summer.
Water moderately but make sure not to over water.
If the pots are likely to freeze in the winter, this may damage the roots, to avoid this you could wrap the pots with bubble wrap or layers of horticultural fleece.