Because of the seeds in grass clippings, I think that using them right out of the mower is not a very good idea.
On the other hand, if you start a compost pile, and put your clippings in there and sprinkle a little 10-10-10 or 5-10-5 and add a little moisture to it every time you add clippings, and mix it up, next year you will have a dandy compost... and the seeds will have 'fermented' with the rest of the remnants. It may not kill all of the seeds, but there won't be near as many as with fresh clippings.
Compost is made better in some sort of container. I have seen them with and without hand cranks. Even a couple of wooden boards, hammered in the ground in a square and dark plastic stapled to the outside makes a good compost bin. You need something to trap the heat and make your 'stew'. The only thing is... it takes alot of clippings to make even a small compost pile.
You would probably do best by not using fresh clippings in your garden. Only Composted clippings will give you positive results without fear of 'seeding' your Garden.