By Isla
Midlothian,
Scotland 
On the packet the photo is red that's all information I have.
Isla
4 Aug, 2014
Answers
Would imagine its when they turn red then - a nice strong well developed red, rather like waiting for tomatoes to ripen. But some reds you can use green as well - if you have plenty why not try one?
4 Aug, 2014
Previous question
« I have got a wilting clematis planted in a large pot, what has caused this?
A picture of the packet would help, Isla.
4 Aug, 2014