Covering the pots the plants are planted in is a good long term idea for thrips, although it won't imediatly decrease the thrips like neem oil it will gradually bring their numbers down over time and stop you getting them in the first place. Thrips lay eggs in leaves, these drop into soil, cover the soil and stop their breeding cycle. Do not cover the soil so that no air can get in as this could be bad, just loosely with a paper plate or somthing, this is a good preventitive and long term control method. If you only have a small indoor garden then you can pick them off youself to keep numbers down till other methods start to be effective. Sometimes it is hard to get rid of thrips and many people with large gardens and commercial operations never manage to totally eliminate them from the garden merely keep the population numbers down so that damage is at a minimun. Ladybirds is a good idea if you can find some in the local bushes, collect a load and let them loose on your plants, will fly off after a few days but not before eating a lot of thrips. Just a few ideas also i never heard of thrips being dangerous in the soil allthough i believe some varieties eat the roots but none that you normally get, should be fine in the soil, its when they get on your plants they start the damage. Good luck with the neem.