Hi I'm Alan from Newlands nursery.
With the heat at it's height, anyone who's done any gardening for any period of time, is going to suffer from a few flies; Greenflies, Whiteflies and more. I noticed, that a few people have mentioned it from plants that they've grown from us, all of a sudden, these Greenflies just appear. It's inevitable horticulture. But we don't really want greenfly or whitefly on our plants. In the video linked below I go step by step on how to prevent this ! I am using Lemon Verbena, but this technique is applicable to any plant !
Essentially, use a spray water bottle with some washing up liquid in it, and spray over, what it would do to the bugs, is it would gum them up, and mean that they're not going be able to live. This is the most convenient, at home and natural way I can advise. Give it a go! If you have any problems don't hesitate to get in contact. See you soon!