It would be possible to plant grass seed after a frost, but if the temperature does not warm up, the grass seed will not germinate. Old time gardeners, where there was a lot of snow, used to plant grass seed just before a snow. The grass would then sprout in the spring, when the snow melted. It would most likely be best to wait till spring to sow the grass, if your area does not normally keep a cover of snow all year. Otherwise, most likely, all you will be doing with the grass seed is feeding the birds and rodents.
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