Mow the lawn in the early morning when the grass is still wet with dew. Use a push lawn mower over an electric or gas, if possible. Rake up the lawn clippings.
Put about 11 lbs. of clippings in a plastic grocery bag and compress it so as much air is pushed out as possible. Tie the bag closed and insert it upside down into another bag. Tie it closed, pushing the air out as you do. Repeat a third time, putting the bag in a third bag, upside down, and sealing it.
Store the garbage bags in a secure place for at least a month. Make sure rats and other rodents can't get at it. Drill holes in a garbage can if you are keeping the silage in there to prevent too much pressure from forming, which causes the bags to stick together.