Posted: 31/05/2014 at 12:00
My concern would be regarding the weedkiller part of the treatment - I've no idea how long it remains active - it might be an idea to try sowing some cheapish seeds - radish, lettuce etc and see what happens.
Do you still have the packet the treatment came in? Does it have contact details for the manufacturer's customer service dept? I think I'd contact them and see what they advise.