sooby said:They wouldn't be in the soil unless they are root aphids, and if they were root aphids you wouldn't be seeing them on the above ground parts. They probably came in with the plants in the fall. Once indoors they proliferate because of comfortable temperatures and no natural predators. It's difficult to blast them off the soft tissue of plants with enough force without damaging the leaves, they can really hang on. Aphids may nor may not have wings, have you seen any winged forms? If so that'll likely be how they're getting around.
BigBill said:All soap and water will do is give you clean aphids.
They could come from your house, a neighbors house, who knows. They travel on the wind.
Bayer's 3in 1 insect spray, follow directions, three sprayings, a week to ten days apart. Spray all the soft tissue parts of your plants. Leaves, tiny stems, etc.