Pinching Out Annuals and Biennials
As the young plants develop, some may require 'pinching out' (or 'stopping') so that they will be encouraged to produce side shoots and develop a bushy habit. However, do bear in mind that pinching out delays flower production and so should not be carried out if an early display is preferred.
Pinching out is carried out nipping off the growing tip the young plant. If an even growth habit of plants is required, pinch out tall plants when they have reached five or six joints by removing the tip of each long shoot back to the required height.
Do not pinch out plants such as stocks (Matthiola) or antirrhinums that have strong terminal shoots, as these develop the main flower spikes and will also produce lateral growths naturally during the summer to continue the flowering display.