I reckon if you de-weed the immediate area and properly dig the ground it should help alot. I don't know what soil your area has, in the south its mainly clay type soil very sticky dense shit and hard for roots to get through, other areas I dunno. What I wouldn't do is mix in really hot shit like manure or similar fertilizer because it takes some weeks for the soil to cool down, it will burn seeds even normal grass seeds. Get a couple of bags of good potting compost, I can get like 3 40 litre bags for ten quid in Homebase but it dosen't cover much if you dispense it over a big area. Apart from that cannabis is really just like any other plant, don't neglect it and it will pay you back by not dying.