Re: Sandy Weed Lot in So Cal
Do not use weed killer! All you'll be doing is killing the green part of the plant and polluting the ground and nothing to the weed seed that is laying dormant or that will be planted while tearing out what you've got. Instead, forget about the weeds and just use a tiller to break the top of the ground and loosen the weeds. Rake out what you can, then apply a good thick layer of soil amendment such as compost or manure. Work that in as deep as you can.
Lay your irrigation system, regrade the area, then install sod. Sod will give you an instant green yard that can be used almost immediately. If you go with hydro-seed or normal seed you'll get spotty results and won't be able to use the yard for months. Sod is a little more expensive initially, but IMHO it is completely outweighed by the instant green and use factor. Also, by using sod you'll be putting down a blanket that will insulate the soil, block out light, and choke out any weed seed from sprouting. The few weeds that you might get will be easily pulled as they appear.