The nasturtium is actually what is known as a trap crop… it doesn’t repel aphids, it attracts them! So if you plant it as a companion plant, it will not solve your aphid problem, but may in fact worsen it, because once the aphids move into the nasturtium, they may make the jump to neighboring plants, especially if there are ants in the sector, as ants feed on aphid honeydew and literally farm them. They won’t hesitate to carry aphids to other plants to help them move onto “greener pastures”.
The end of the afore-mentioned sentence is: … “and when you see aphids on the nasturtium, pull it out and destroy it to crush the infestation in the bud”.
It’s so simple, but you still have to do it.