Are you on organic soil?
Organic control: Spraying just about anything every three days for nine days will get rid of them. Garlic-pepper tea and seaweed mix is one of the best sprays. Citrus oil sprays are also effective.
I'd also try BT, soapy water spray w tea tre oil/neem, maybe beneficial nematodes. I'm sure others will offer some proven methods. I'm still battling fungus gnats.