We have two raised beds that we would like to put vegetables in however last year carrot fly and slugs had a lot of the veg. This year I want to do things differently. I have turned over the soil and plan to put a bag of manure (from the garden centre) on each bed, but not sure if I can plant immediately after adding it? My plan is to put onions, beets and leeks in one bed and carrots, celery, lettuce and radishes in the other. I have heard that nematodes kill slugs but have never used them. Do they work and can I plant directly after using them or do I have to wait? As regards carrot fly, is there any way of stopping them completely? Any advice would be greatly appreciated. Thanks.