It's all down to the position and soil type that controls whether a grass runway is useable in winter.
We spent thousands on drainage and looking after the runway throughout the year, but no matter what, it always became a quagmire. Eventually we gave up and put down a tarmac strip and crossovers. Now we can operate throughout the year.
If you are on top of a hill and have chalky, well drained soil, then you have a chance of keeping the runway useable, but even then it is a battle. If you are at low flat levels with clay soil, then you are stuffed already and you'll just end up wrecking the grass for the summer if carry on by rutting the surface badly and turning it into a mud pit.
One final tip, when the ground is drying out during spring, get the roller onto it before it hardens totally, that way you can get the worst ruts out of the ground before they are set like concrete that are virtually impossible to flatten properly.