Possible mulching materials include straw, crushed corncobs, chopped cornstalks, sawdust, wood chips, dried grass clippings, and shredded leaves. The depth of mulch needed depends on the material used. Optimum depth ranges from 3 to 4 inches for fine materials, such as sawdust, and from 8 to 10 inches for straw on well-drained soils. Avoid deep mulches on poorly drained soils to discourage root diseases. When mulching red raspberries, apply the full depth of material between rows. Within rows, apply only enough material to control weeds, allowing new canes to emerge in spring. Since organic mulches gradually decompose, apply additional material each year.
Weed control in raspberries is necessary to reduce competition for water, nutrients, and sunlight. Cultivation and mulches are the most practical control measures for home gardeners. Cultivate the raspberry planting frequently during the spring and summer months. Small weed seedlings are destroyed easily. Large weeds are more difficult to control. To prevent injury to the raspberry plant roots, do not cultivate deeper than 2 to 3 inches.
Several herbicides can be used by commercial raspberry growers to control weeds. Herbicides registered for use on raspberries can be found in PM 1375 Midwest Commercial Small Fruit and Grape Spray Guide for 2004 .
Spread 3 to 8 inches of an organic material mulch like dry grass clippings, shredded leaves or straw between the rows and plants. The thickness of the mulch layer should vary depending on the material. For example, a 6- to 8-inch layer of straw is needed to effectively block weeds, while 3 inches of sawdust may perform equally well.
Spray a non-selective herbicide such as glyphosate only on the weeds, taking care to avoid contact with or drift onto raspberry canes or any other desirable vegetation. Alternatively, you can apply a herbicide that contains paraquat or carfentrazone to the entire mature raspberry stand to control weeds and green, first-year canes.
Pull small weeds up by hand, or shallowly cultivate the area with a hoe or similar implement. Break up no more than the top 2 to 3 inches of soil, and leave ample space around the canes to avoid accidentally injuring the canes or roots.
Raspberries (Rubus spp.) and other caneberries are prized for the large number of flavorful fruits they can produce. A number of factors can negatively impact raspberry yield and fruit quality, including moisture stress; inadequate or excessive nutrients; pests or diseases; and weeds that compete with the raspberry canes for water, nutrients and light. Weeds near plantings can also harbor potential raspberry pests and diseases. Clearing an area of weeds and weed seeds prior to establishing a raspberry planting can reduce the presence of weeds for several years, but weed control around established canes is still eventually necessary.
Mow, trim, pull or use a non-selective herbicide such as glyphosate to address weeds near the raspberry planting or garden before they go to seed or, in the case of creeping perennial weeds, grow into the planting.