I am very new to gardening and made a really big mistake when tilling a new bed in my yard. We decided to put it in an area where we used to have bird feeders. We tilled down several inches and then mulched. Two days later we planted several shrubs and perennials in the new bed. It looked fabulous until the next morning when we found dozens of sprouts coming up throughout the bed. We pulled them but just hours later dozens more came up. Upon some research online, they look to be sunflower sprouts. Is there anyway to stop them from coming up without digging up everything and starting from scratch? I really don't want to risk losing hundreds of dollars worth of plants but also don't want to either spend weeks pulling up sprouts every day or ending up with sunflowers growing all over my manicured bed. HELP!