Posted: 24/06/2014 at 21:57
If you must use washing-up liquid, just a few drops in a bucket of water. The proper stuff to be using is horticultural soft soap, to be honest.
If you want to zap your aphids in an organic way, make up an extremely effective insecticidal spray from rhubarb leaves & water....this uses the oxalic poison present in the rhubarb leaves.
Kills caterpillars and other nasties too.