The only natural weed killer IMO (besides boiling water - on patio slabs) is elbow grease.
If you find a reliable source of the stuff do tell
We tackled our garden with a strimmer and a rake, loppers, a spade, a pushmower and plenty of elbow grease and a year later most of it is now under control - it was also a jungle I don't know it's size in feet but it is 89mx11m... so pretty big
Stick at it splot, you'll get there
