Q: Can you tell me how to prune a purple smoketree?
A: Mercy! There are statements of absolute conviction saying opposite things!
I think it is possible two avenues of confusion arise: if a gardener desires great looking foliage and doesn’t care about flowers, late winter pruning is in order. It is also possible that Cotinus coggygria ‘Royal Purple’ is able to flower on “old” wood that has grown in the current year.
Flowering in June might give time for winter pruned smokebush to grow spring shoots and harden them off to produce flower buds in summer. Perhaps the other smokebush (C. obovatus) requires a longer time to harden and should only be pruned after it blooms the previous year.
In any case, you can’t go wrong if you prune your smokebush after bloom in early summer.