Posted: 08/07/2015 at 18:17
I think if I was you maybe I would look for a cheap metal arch that would fit into each end of your planter and grow tall grasses in the middle and maybe a clematis to cover the arch, you can buy winter clematis or spring ones that keep their leaves all year and are quite vigorous like the armandii Snowdrift which is a lovely white flower and tough dark green leaves that stay all year.
The other thing is to buy a trellis to fix on top of your fence which is criss cross with thin wood, you may see these for sale at boot sales also garden centres sell bits off like this at this time of year so check them out for a bargain.
Trellis add height and privacy with or without plants, but are perfect for climbers.
I do agree with hogweed, nothing will be instant but the sooner you start the better. Good luck, I hate nosey neighbours.