I have been experimenting with buckwheat and elbon rye.
I first started planting 8-4, and planted four plantings of buckwheat at four day intervals. Then on 8-19 I planted a small strip of rye. All came up and doing well, but the heat and insects plus all the water I am using makes me think I should have saved my money and bought compost when I need it.

I do plan on planting a cover crop of elbon rye and hairy vetch in about 2 to 4 weeks. Its just too hot and dry here to grow anything.

I have never grown oats but I expect they would be much like rye.

Larry

The standard time to plant winter cover crops in Oklahoma is about mid-September. (Maybe a bit earlier for those in extreme northern OK, and maybe a tiny bit later for those in extreme southern OK if the heat is hanging on into mid-Sept. and little rain is falling.)

Although most cover crops can be planted in mid-September and will grow just fine, the other 'general' recommendation is to plant them at least a month before you average first autumn freeze date.

Cereal rye, like Elbon, is the exception to the rule. It can be planted late...right before the first expected freeze...and will sprout and grow well.