Deadheading is removing spent flowers so that you can encourage the flowers to grow again. If you don’t deadhead in your garden, not only does it look ugly, but at the same time the plant doesn’t know how to generate.
Remember: the flowers are coming because they want to reproduce, so if they go to seed, then of course they’ve finished. So, what you want to do is cut it off before they go to seed and therefore you get more flowers.
For more information, consult the OSU Master Gardeners Hotlines:
Jackson County: 541-776-7371
Josephine County: 541-476-6613
Klamath County: 541-883-7131
Curry County: 541-247-6672