If Diana's advice does not work, do a mixture of dish washing up liquid soap and water, that will help too, you mist this onto the plants and remember with both ideas, you need to spray or mist the undersides of the leaf too as lot's or most Aphids are hiding /laying eggs there.
It is advisable to repeat the treatment maybe 2 times a week or more, as the adult Aphids will be easy to remove by both methods BUT, there could be merging new ones or eggs laid for later hatching so make sure you do it often enough till the whole plant is clear,
Good luck and best Regards.
You can buy NON chemical washing up soap now-a-days, introduced because of skin ailments some people were experiencing, the soaps ALL have some amount of oil added to help keep humans skin supple however, this also helps the mix sticks to the skin of the aphids, they cant breath and they cant move about on the plants, it prevents them mating and laying more eggs.
Also when I said a mixture, I was not talking about a whole bottle of soap, I was talking about a few drops of soap to maybe 2 pints of water, you will get more bubbles than troubles with that weak liquid mix, I've been doing this for as long as I've been gardening as have everyone else I know who dont use chemicals on their plants and there has never been any problem.
I'm sure there will always be someone somewhere who would worry about household products being used but this is one product that is really very safe.
I fully understand your concerns Purpleinopp, but can honestly say, I would never give any advice to others that was unsafe, don't work or have not used myself, and have a proven record of harmless usage that works.
Ladybugs will eat your aphids. If you get the adults, try putting mosquito netting over your plants so the ladybugs can't fly away until they've eaten all your aphids (maybe a week or so?) Have to remove it eventually, of course, for your plants to be pollinated.
Lacewing and Ladybug nymphs, hatched from eggs that you can purchase at a gardening store or online, work really well. They cannot fly yet, so they stay on your plants till the job is done!
Great advice from TomatoMum, the Nymphs need hundreds of aphids each day to survive, and they are not any danger to other insects or plants, good idea also to net the plants that your treating as these nymphs are food for other bugs, jeeees isn't nature wonderful LOL.
What Ive done with my hibiscus and roses which were getting aphids (I also did this around the non affected plants as a preventative too), was I planted a ring of garlic around the plants. It also has the bonus of looking quite attractive when the garlic is flowering and of cause I can eat it too. Ive noticed far less aphid issues since Ive done this.