Potential for Injury to Container Tomatoes when Mulched with Grass Clippings from Herbicide-treated Turf

Grass clippings are recommended as a mulching option for home vegetable production. To avoid the potential for herbicide injury, most labels for lawn weed control products (and many Extension home gardening publications) warn that clippings collected from herbicide-treated lawns should be used with caution in vegetable gardens. The required waiting period on some product labels, from time of herbicide application until clippings are considered safe for use in the garden, varies from a few weeks to the entire growing season. A review of Extension gardening publications suggests waiting periods of anywhere from two weeks to several months. There appears to be no published research on which these waiting periods are based, and there is little consistency for suggested waiting periods for safe clipping use in Extension literature written for the home gardener. Our research examined the effects of grass clippings collected from Kentucky bluegrass (Poa pratensis L.) turf that had been treated with broadcast applications of highest label use rates of 2,4-D or quinclorac. Clippings were collected 1, 3, 5, 10, 15, 20, 30, and 40 days following application of each herbicide and were applied as mulch to tomatoes (Solanum lycopersicum ‘Celebrity’) planted in #5 black plastic containers. Plant growth (height, final shoot, and root weight) and fruit yield were measured.