Can I train nasturtiums up a fence and if so I assume they would require tying in?
Yes on both counts.
Yes to both questions -you will obviously need a special variety.
Thanks. What special variety would that be?
Sorry-a climbing or trailing type.
There are "climbing" varieties available - they are longer than the normal plants, and will ramble through or over other plants if left to their own devices.
I grew 'Cobra' last year and would recommend it.
Sorry, Geoff - I seem to be posting at the same time as you continuously today!