The earlier the better but after mid September not as much growth as I would like
Here in Hartland, zone 4, we count on getting a good stand if we plant oats & peas no later than Sept 15th.
For planting garlic into a living mulch we aim to sow oats & peas by August 15th .
mid sept can still leave you with an ok stand... also it'll be more
workable in the spring. Mid Aug. is ideal for biomass, but that leave
excess spring residue that makes field work hard - esp. plastic
mulching. good luck!
Always worth a shot. If it's probably too late I skip the peas, but oats are so cheap, worst case scenario you feed some birds, and even if you don't like birds you gotta benefit from them pooping.