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Short-season cover cropping can be an important weed management tool. To optimize the use of mustard [Sinapis alba L. and Brassica juncea (L.) Czern.] in the Great Lakes region, we assessed planting time effects, mustard biomass production, and weed suppression during mustard growth and after incorporation. The study was conducted in Illinois, Michigan, and New York for spring and fall from 2010 to 2012. Mustard was sown every ~10 d from mid-March to early June for spring plantings and from early August to mid-September for fall plantings. Spring mustard biomass, weed density, community composition, and dry biomass were collected at mustard flowering. Fall mustard biomass, weed density, and dry biomass were collected at season end. Spring mustard biomass ranged from

Mixtures of cereal rye (Secale cereale L.) and the legume hairy vetch (Vicia villosa Roth) are used to provide fixed N in balance with other important cover crop services, but late planting and interference from rye can limit vetch productivity. This 2-yr study in Michigan investigated how fall planting dates influence rye–vetch cover crop biomass quantity and quality in the spring, and evaluated whether staggering (delaying) rye seeding could improve vetch performance (biomass production, N fixation, and winter survival) in mixtures. Treatments consisted of a two-way factorial of three vetch planting dates (late August, mid-September, and late September) and three lengths of rye seeding stagger (co-seeded, short stagger, and long stagger). Later planting of co-seeded mixtures generally led to reduced total shoot biomass and lower proportions of vetch, resulting in cover crop residues with less vetch N and a higher total C/N. For earlier planting dates, delaying rye seeding until vetch emergence (short stagger) increased vetch shoot biomass by 760 to 1060 kg ha–¹ (30–36 kg vetch N ha–¹) relative to co-seeding. Staggered seeding provided no benefit to vetch biomass at later planting dates, and delaying rye seeding until the vetch three to four leaf stage (long stagger) reduced vetch winter survival by 12 to 42% compared with co-seeding. Additional research is needed to determine whether potential on-farm benefits of rye–vetch staggered seeding justify the additional management complexity involved and possible tradeoffs with other cover crop services.