Grasses in raspberries
Thank you for your question. It is good that you are thinking about eliminating the competing grass from your garden.
The preferred way to control weeds near plants you eat off of is by hand pulling, hoeing, or tilling. The weeds are easier to remove the day after a rain or a good watering. Hoeing or tilling should be done carefully and shallowly as not to damage desirable plant roots. Keeping up with this practice throughout the growing season will keep the grass from growing to seed and spreading.
Depending on the size of your raspberry patch and the amount of grass in there, this may or may not be doable. If a chemical option is indeed needed, we recommend a selective postemergent grass herbicide such as sethoxydim. Be sure to refer to the label for recommended application timing, rates, and specific vegetables and fruits it can be used on. Also be aware that some herbicides used on or near fruits and vegetables have a “days-to-harvest” restriction meaning that you can not harvest or eat the fruit until after the recommended amount of days. According to a Cornell University bulletin, sethoxydim has a 45 days-to-harvest with raspberries. Again, read the label very carefully for the product you intend to use.
Once you have the weeds under control, adding a three to four inch layer of organic mulch (straw, leaves, compost, wood chips, shredded bark, and pine needles) will help suppress the growth of weeds. Some of those mulches breakdown faster than others and may need reapplication every season.
For more information about growing raspberries in the home garden here in Minnesota, here’s a link to a wonderful resource: https://www.extension.umn.edu/garden/yard-garden/fruit/raspberries-for-the-home-garden/