Yes, it may bear more flowers actually, as the hormones will be slowed down by the stem being sideways and won't all rush to the top of the stem. This is the reason why apples etc are trained into espaliers or cordons. It's called 'apical dominance'.

But, you'll get shorter flower stems. A friend of mine shows them nationally, and always brings my mum the 'throwaways', which are magnificent. His back garden is put over to growing sweet peas, and he trains his up sticks, then bends the leading growth down and grows it up again to produce more flower. What I'm getting at is that for show quality, you need big flowers on long stems, and that's why he does it. Ergo, upright plants produce bigger and better flowers. Phil

Thanks for that! I'll give it a go next year and try them as a screen. Thanks again.