My experience, at least of L scoparium, is that they are rather like ceanothus and leyland cypress in that they don't seem to reshoot from areas of dead leaves. My leptospermum scoparium "red damask" proved rather hardier than the -5 to -6 that was quoted for it, and passed through several -7 winters undamaged (though these -7s were always only brief), and even the (very brief) -9 we had in the 08/09 winter. But the prolonged cold of 09/10 did for it, even though I never recorded below -6 that winter. Another one with white flowers was killed rather more easily.