I took lots of solamum crispum cuttings for the first time last year . I started mid July and finished about mid September. I'd say Mid August is the perfect time.

I took 6 inch long pencil thickness cuttings (or a bit thicker )and put them 10 to a one litre pot containing a mix of one part horticulturtal sand to 3 parts potting compost. I put them in a shaded coldframe.

They root in about 3 - 4 weeks.

Here they are

http://www.flickr.com/photos/31559373@N00/5022442509/

I had a 100% success rate and I would say they're one of the easiest cuttings to root.

I over wintered them in an unheated coldframe outdoors and they survived -12 centigrade

I shall be potting them up into individual pots soon

This is a good article on solanum

http://www.telegraph.co.uk/gardening/howtogrow/7846747/How-to-grow-Solanum-crispum-Glasnevin.html