How to Pinch: To pinch your begonias you need to remove the growing tip of each stem where the next leaf will come out. Usually you remove it by pinching it off with your fingernail (yes, that’s why it is called pinching and no, I don’t know who thought of calling it that). Make sure your remove the bud and the new baby leaf below it to make sure you get it pinched off.
When to Pinch: On plants that you’re going to pinch, start pinching after pruning out three nodes (a node is the joint in the stem where the leaf is connected). The reason for this is that if you don’t wait until you get out three nodes then you won’t gain anything because after pinching out one bud where would it branch from? With three nodes, after removing the one node (the growing tip is a node too), then you are left with two nodes that will send out side shoots. These you let grow out three nodes and then pinch again. Usually a plant that is actively growing can grow out three nodes in three or four weeks. You continue pinching until about 6 weeks before a show to make sure the plant has time to grow out and bloom well in time for the show. Pinching will delay blooming, but you will be rewarded with so many more stems that have blooms that it is well worth the extra wait, besides the fact of how nice and full your plant will be.
I was amazed at the difference pinching made especially on plants that had a tendency to become leggy and sparse. If you plan on entering shows and would like to win something for your efforts then you really need to learn to pinch to have quality show plants, but even if you’re just growing them for yourself you should still pinch for beautiful full plants.