You can cut them back now, early May is the best time just as the amount of sun increases, how much depends on how big it is and if its become leggy or not. You need to encourage a bushy plant so anything from half down to two thirds in a neglected plant. With containers layer some lower branches into the soil or build up the level to cover the lower stems. This will encourage new growth from the bottom. The stuff you have cut off can be used for cuttings, they root very easily in mpc mixed with sharp sand.
Everyone who said the black was down to overwatering: you were right. I had a proper look and I had been deceived by the fact that the soil round the edges of the pot was very dry. Despite using a very free-draining mix with plenty of gravel, perlite and sand, there was a damp patch around the roots of the plant which did not seem to be draining so well.
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You can cut them back now, early May is the best time just as the amount of sun increases, how much depends on how big it is and if its become leggy or not. You need to encourage a bushy plant so anything from half down to two thirds in a neglected plant. With containers layer some lower branches into the soil or build up the level to cover the lower stems. This will encourage new growth from the bottom. The stuff you have cut off can be used for cuttings, they root very easily in mpc mixed with sharp sand.
Thanks Dave. I'll do that.
Everyone who said the black was down to overwatering: you were right. I had a proper look and I had been deceived by the fact that the soil round the edges of the pot was very dry. Despite using a very free-draining mix with plenty of gravel, perlite and sand, there was a damp patch around the roots of the plant which did not seem to be draining so well.
Lesson learned!