Preen One Lawncare Preen One Lawncare is an easy one-step application for spring lawn care. Preen One delivers three lawn treatments in one application: stops crabgrass all season, kills dandelions and most lawn weeds, and feeds your lawn for 8 weeks. Transcript Preen One Lawncare: It's time to rethink your lawncare routine. Preen One delivers three essential lawn treatments in one. This one-step application for spring lawncare feeds the lawn for 8 weeks, kills over 250 lawn weeds commonly found in home lawns including dandelions, chickweed, thistle, clover and more. For a complete list of weeds, see the product label. Choose the one that's only one so you can spend more time enjoying your lawn and less time working on it.