No, it won't work. Root maggots are the larvae of a fly that will come back and lay its eggs in whatever soil you have in that spot. Try crop rotation and floating row covers.

I kind of figured that they would come back because of the damn fly. I wonder why my neighbors don't have the same problem. Our gardens are separated by a simple wooden fence and they had plenty of onions planted right next to it. Their garden has been established for years.

My garden area is quite small (I can barely use an entire packet of seeds when I plant) so I doubt that rotating will be very effective. What about wood ashes, how effective are they really? As for ground covers, I've read up about it but I'm still not sure about how to do it. I'd need to see a few really good pics (I'm a visual person).

Anyone know of any products available in Canada for this type of problem?

I wet the row with a mixture of vinegar and water for onions before planting. No maggots in my onions. Haven't tried it on carrots tho'.I am from central alberta.

I plant onion sets just deep enough so as the tips are sticking out of the ground. When the plants have begun to nicely established themselves, the soil is carefully pulled away to the base of the bulbs, yes some of them will then flop, though most will soon right themselves. We never again have had maggots in the onions when using this method. This also works quite well for turnips.

Terrance