Answer: This shrub usually blooms for a fairly long period, possibly into July. After that it forms berries where the flowers were. If you prune it back in spring and summer you will remove the flowers/berries, some people consider them one of the ornamental features of the plant. In any case I would prune no later than mid July. The reason is that the pruning will usually encourage further growth and you want it to have time to harden off before the cold weather starts in. If you truly want a hedge, you could trim it repeatedly, cutting it off quite short. This will stimulate branching each time you cut it and make it grow dense at the base. On the other hand, this plant usually grows quickly and spreads out naturally, it is a big plant. You might want to wait and see how it does on its own. Either way, if you do not like the results, you can trim it off at the ground in late winter or early spring and let it regrow. This type of renewal pruning is usually done every few years to keep the plant in bounds. It's always hard to wait for things to grow toward their mature size, but there is no way to rush nature. Enjoy your Diabolos!
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