A couple of weeks ago we did a big weed tidy up out in the front yard - we pulled up lots of couch and kikuyu - I did not want to put it in the compost heap because both these grasses are invasive and spread by runners and they don't die in the compost heap.
So I put them into a spare wheelie bin we have here and filled it with water - covering the weeds.
That was about 2 weeks ago - we now have one batch of smelly weed compost tea or extract.
But once diluted to tea strength it is a great fertilizer for the garden.
What a great way to get those nutrients and other goodies out of a weed - once we have used the liquid the grass should be well and truly dead and it can go onto the compost heap.
There are lots of links to compost teas and extract - check them out here and here and here.