Annuals bloom better if the old flowers are removed. This prevents seed formation that normally makes annuals start to decline. The practice is particularly important when growing ageratum, calendula, cosmos, marigold, pansy, rudbeckia, scabiosa, verbena, and zinnia.
Make sure that you have an adequate way to remove dust and fumes from your workshop. If your workshop has two windows that face each other, open one and put a fan that blows outward in the other. If not, an exhaust fan should be installed.