Sunn hemp is a leguminous cover crop, so it adds nitrogen to the soil via its root system and once tilled in, all other parts of the plant, flower, stem and leaf will also be useful accessible nitrogen for your next planting. Nematodes do not use sunn hemp as a host, so planting your garden with it can help starve them out of your soil. Also, having something planted in your raised bed in the summer will provide a few complimentary benefits for your soil. We always say that "nature hates bare soil" and if you think about it its pretty true; prairies are covered in perennial grasses, forest floors are strewn with decomposing leaves, and languishing construction sites soon end up covered in "weeds" and natives being brought in by birds and the wind. If left bare your garden will be subject to erosion from extreme rainfall and nature will eventually cover it with weeds for you. Also, the complex web of soil life that you've been nurturing and tending to in your garden with your homemade compost and organic fertilizer all need roots to use as a home and a food source, and so without homes those microbes, worms, and other life forms will likely die, leaving you with less alive and undernourished soil come fall. 

To use sunn hemp cover crop properly broadcast seeds densely, water daily for about 10 days while they germinate and establish themselves, and then cut it all down at about 60 days, before flowering. Letting the sunn hemp get too mature will leave you with thick fibrous stalks that can be hard to manage (sometimes even our commercial grade mower has a hard time with the stalk of a mature sunn hemp plant) and those stalks will decompose once cut down much slower. Theres a helpful video of us cutting down and smothering a sunn hemp crop here on our IGTV. Once the sunn hemp is cut down we like to cover it with some garden soil and hay so we can sequester its nitrogen before it dries out on the surface. 

Our 1 pound bag of sunn hemp comes with a bit of legume innoculant sprinkled in so that you can use it right away and make sure to get nitrogen nodules in your roots, and a one pound bed is a good amount to cover one 4x8 foot raised bed.