Posted: 23/07/2013 at 11:19
In that case they are probably congested and need lifting and dividing to re-invigorate them.
You can do this from mid summer to early autumn while they're still green but you must water them thoroughly first and leave them to soak it up before you dig up teh clumps. Then you can split them with a spade and replant them in well prepared soil containing lots of well rotted garden compost and/or manure to feed them and help retain moisture. I would chuck in a couple of handsful of pelleted chicken manure too.
Once re-planted, they will need monitoring and regular watering until established, established if you do it sooner rather than later.