I read about the value of adding worm castings to minimize damage from pests. I'm amazed! Not one of my roses had aphids on it this year. I mixed it in with the soil I use for my lettuces, and then did a small lettuce container without it. The small lettuce container was filled to the brim with whitefly, but the crop with this product was virtually pest-free.
While worm castings are rich in nitrogen, I would never use them as a single source of nitrogen. Will it add organic material and micronutrients to your soil? Yes! That's always a good thing. But it shouldn't be your single source of fertilizer.
I like to work this into the soil as best as I can and then top with a layer of mulch. For containers, I just mix it in well with the potting mix. You want this to get to the roots of your plants so they'll absorb the chemical that kills insects. I'm interested to see if this will help with fungus gnats since I always seem to be cursed with a fresh bag of potting mix that contains nothing but gnats...
The price is expensive, but it beats buying and spraying pesticides, no matter how organic they may be. I'm an inherently lazy gardener so something I can just add to the soil that will keep large infestations at bay is worth the price. I bought two 30-lbs bags this year for our very old orange tree so we'll see if it helps with that as well.