How do I trim poinsettias?
I prefer to wait until spring. If you are forcing it to bloom (dark treatments should have started October 1st to get flowers by Christmas) you need to wait until after you have enjoyed the flowers. If you are growing the plants just for the leaves you can lightly shape, as needed. Wait until spring when the days are longer and the light intensity has increased to do major pruning. The better growing conditions will help the plants recover quickly.