I would go with water too, I never feed the runners a supplement whilst growing , just make sure when they are planted that I have dug in rotted manure deep down where the roots will go.
My 1st lot of flowers were pretty hit and miss at setting this year but a second lot (after my 1st pickings) seem to be doing so much better, not just a coincedence I think that the showery weather is back and keeping them watered.