I have two containers of ivy and assortments that have gnats in them. What’s the cause? I’m thinking that watering is probably the problem. What should we do? I’ve now got the plants on the patio and I’m hesitant to bring them in the house because I don’t want any gnats in the house. I’m thinking I need to spray the entire plant with some kind of spray, but what?

A lot of the time these are fungal gnats and are caused from over watering or water remaining in the saucer or bottom of the pot. I would take them out and repot them with new soil. This will do away with their “home-like conditions” then it should be ok. You could put them back in the same pot, after you have washed the pot. You could give them a drench with safe houseplant spray and try to get rid of them but I think getting rid of the contaminated soil is the best. Sometimes they also gather in the saucer when there is water left in it. Hopes this helps. 
r2-2015