Hi Sidd,

Even with a healthy invasion of aphids, they are really easy to get rid of.  First by hitting them with a hard water spray, then using insecticidal soap which you can make at home.  

You are probably right that removing the nasturtiums will move them to another plant.  

Insecticidal soap is a tablespoon of liquid soap usually Castille and a tablespoon of oil then fill the squirt bottle with water and shake.  Do not use Dawn it will take the waxy finish off the plants.  

Spray both sides of the leaves and stems.  Do not spray the flowers as it will kill pollinators too.  

I would use the hard water spray first, put on gloves and gently remove any left with your thumb and forefinger.  Being soft bodied, this will kill them. 

Washing the plants with water will remove most if not all the aphids and they cannot get back up to the plant.  There are a few that are winged but most of them are born on the plant.

You can use yellow sticky paper however, there are very few winged aphids that are not on the plants.  

By the way, aphids are born pregnant and it is said that they can produce thousands of eggs each. 

There are two insects that eat a lot of aphids.  Lady bugs and green or brown lacewings.  Adult lady bugs often fly away but you can purchase eggs for both insects.  Google predatory insects for sale.

Here is a link to an article from Oregon State on aphids: https://extension.oregonstate.edu/news/how-control-aphids-less-toxic-methods

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