I adore nasturtiums but ,yes,very prone to blackfly,have heard to use soapy water on them,but does anyone know of some to prevent them in the first place?
There are many plant 'companions' which help each other out in this way. I always sow onions with my carrots. The onion smell masks the carrot smell so carrot fly can't find them so easily.
Nasturtiums help keep wasps away from the house, as wasps are extremely fond of blackfly. Just don't plant them too close to your house.
Hi SpikeyBush,thanks for the tips,have planted them in tubs so as not to contaminate the rest of the garden,not sure where their final spot will be,but will take on board what you say about the wasps...thanx