Aphids on indoor seedlings

Got problem with aphids in the house this Winter. Don't know why - stunted/killed all my nice cole seedlings before I realized what was wrong. Only spread to peppers, okra, and sweet potatoes - but I was able to save with purchased, OMRI, insecticidal soap. Used only new, clean potting soil - but some of my pots were re-used from last year, though they were never outdoors last year except for transplanting..
All my "pots" are "recycled" yogurt, cream, etc containers ... should I wash them every Fall? ... with what?
Thanks to "neighbor" Mike and anybody else who wants to advise.

I had them in my greenhouse too so I'm all ears.  They were on my peppers and sweet potatoes.

i do a combination of 3 things:
- 1 tsp neem oil per 2 cups water, sprayed with spray bottle every few days.
- a light dusting of diatomecious earth through a hand-pump duster
- picking them off by hand and smashing them between your fingers

look for any plants that are their headquarters... i had an overwintered kale plant in the greenhouse that was the base of their operations

Thankfully I didn't have aphids on my houseplants, but I certainly did in the greenhouse attached to my house for the winter.

Eliot Coleman posits that aphids proliferate when the plants are fertilised. So I've stopped fertilising the plants in my greenhouse from mid-autumn on through winter, and that seems to help, but I still get some aphid problems. I squish them regularly in the winter, think of it as massaging my plants gently. It is difficult to massage the tiny seedlings without damaging them, though.

I don't have a greenhouse though my method seems to work outdoors so it might work in a greenhouse.

I spray the leaves of the plant with a mild solution of water and a few drops of dish soap.

I use a cheap spray bottle that I got at the dollar store.

This soapy water solution is sprayed every 2 or 3 days for maybe 2 weeks.

Abe Coley wrote:i do a combination of 3 things:
- 1 tsp neem oil per 2 cups water, sprayed with spray bottle every few days.
- a light dusting of diatomecious earth through a hand-pump duster
- picking them off by hand and smashing them between your fingers

look for any plants that are their headquarters... i had an overwintered kale plant in the greenhouse that was the base of their operations

My greenhouse got down to 21 degrees this winter but I still had aphids come spring.  Maybe the eggs can handle a bit of cold?  They appeared first on the new leaves of my citrus.  I sprayed them with neem and/or insecticidal soap and while it eventually took care of the aphids, the new leaves died.  I'm not sure if it was from the spray or the aphid damage...

Regarding DE, I thought it was for hard shelled bugs.  So would it have any effect on aphids or just their predators/supporters?  I've used it before when I have aphids on my young fruit trees.  I put it around the base of the tree to take care of the ants that are farming the aphids (they have to cross the DE to climb the tree to go to work).  Once the ants stop farming, the aphids get taken care of by other critters.

I had them on my asparagus seedlings under the grow light.  The only thing I can figure is they rode in with the tomatoes and peppers when I brought them in when it got so cold.  Oddly, I didn't find a single one on those tomatoes, peppers or any of the other seedlings.  Finally took care of them with a dish soap and water solution and hand squashing.