Sedum "Autumn Joy."

Hi. Is this time of year too early or late to prune Sedum Autumn Joy? I read elsewhere that people either prune after flowering, or in early spring when new growth appears. if I opt for the latter, when would be a good time? And how do you prune the Sedum without harming the new growth? Where does this occur and how is it identified?
Perhaps the dead flowerheads could just be chopped off as they are rather unsightly - or do they act as a shelter?

 

Simon - you don't need to prune it (ie cut off growing tissue) at all. At the moment the new growth is starting which you can see as little purple blue buds at the base. And all you need to do is to remove all the old dead flower heads and stalks from last year. You can do this by twisting and shaking them, but the more stubborn ones need to be cut off as low as you can with secateurs.

I don't prune mine, but Sedums can traditionally be given the Chelsea chop. That is to cut them back by one third to one half at the time of the Chelsea flower show. This will delay the flowering a bit (but not much) but the reason for doing it is to get a more compact shorter plant that doesn't flop.

 

So I suppose the dead brown stalks can just be left.
I did read that Sedums should be cut down to a couple of inches, maybe dug up and divided - but maybe this was a general thing rather than specific to the "Autumn Joy."

On the issue of dividing Sedums, though - the clump I'm thinking of is quite a large cluster of Sedums. If I were to divide, when should I do it, and ought I to try digging up the whole lot (about half a meter by half a meter), or just slice the root ball into segments as I go?

 

Simon the dead brown stalks are just that - dead. All of last years growth will be dead now and should be removed. Some people like to cut them back in the autumn, in which case you can cut everything to within an inch or less of the ground. Being in a colder part of the country, I like to leave the old growth (of everything) on over winter. It gives a bit of protection, and also gives a bit of winter interest. Flat brown earth would be a bit booring. I then have to cut it back at this time of the year, once the worst of winter is over.

The principle is that herbaceous plants (like sedum) are plants which hibernate over winter below the ground. That way they avoid the worst of the frost. Anything above ground is dead and should be removed at some point. All the new growth will appear from ground level.

Having said that, there are also shrubs. These are plants which don't hibernate. They often loose all their leaves, but their stems remain above the ground and the new growth will appear as buds from these stems. As a result of growing from old wood, shrubs can get very woody. So with shrubs you don't cut them down to the ground, though you can prune them to reduce their overall size or to improve their shape.

The problem then is - what plants are herbaceous and what plants are shrubs. Sometimes plants that we think of as herbaceous like Penstomen are really small shrubs. Though you can usually cut Penstomen back to ground level as well.

As far a division is concerned it doesn't really matter whether you dig the whole plant up or just cut bits off in situ. I would be inclined to dig the whole plant up - with as much earth as you can. You can then put it on a bench, and you will be in complete control. With an old bread knife or a saw you can cut it into as many pieces as you want. Usually the outside part is the younger more vigorous part, which you want to keep. And the central bit will be older and more woody, which you can throw away. But have big chunks - they are much more likely to survive than very small pieces.

 

What Peter says!:gnthb: