It would seem that you can buy heat-treated, and screened top soil from specialist suppliers but at a premium price. I would buy ordinary top soil and leave it unplanted and let it stand to see what in the way of weeds germinate. Let them get a reasonable size (but not run to seed) and then spray with glyphosate. You might have to repeat this a couple of times before planting.

Thanks Jimmy. Your idea is good, but I think I'd end up missing a planting season. Maybe it's worth paying more if I can find the right product.

Screened and graded topsoil is best - there's always a risk of ending up with motorway spoil or some such otherwise. Haven't heard of heat treated - I wonder how much they heat it, because too much might mean its sterile, with no soil organisms present, and that will lower its fertility.

Once you put down the top soil, apply a couple inches of mulch. Mulch serves a few purposes; it conserves moisture so you won't have to water as much, it prevents weeds, it adds a finished look, comes in various colors & materials, organic mulch breaks down and builds the soil structure, mulch helps prevent soil erosion.

For example take a look a Sheila's garden layout. See how she used the stones in one area and bark chips in another area. That's what I'm talking about.

Link: http://www.growsonyou.com/sheilabub/blog/31904-garden-layout-complete

Thanks all.