I have a small (about 1 ft high) purple sage Salvia officinalis 'Purpurea' which is the first I have ever managed to get to survive in my garden. It is looking decidedly tatty and now that winter is over, I'd like to tidy it up. My first thought would be to pick off the tatty leaves and also take about a couple inches of the tops to encourage fresh leaves, but would this have the desired result? I have been told that I can't cut it back hard to the wood.