Today 
Valerian, Centranthus ruber, is a pretty plant that produces bright pink-red, fragrant flowers from late-spring to late-summer, but it also produces masses of seed that germinates all over the garden. Butterflies love it, so if you want to encourage wildlife into your garden, keep a few stems of valerian for them. There is an ornamental white form of valerian.
Solution
Organic
The best organic control is digging the plant out and trimming it to keep it in check if you don't want to remove it altogether. If you see seedlings appearing, hoe them off or pull them out by hand.
Chemical
If you don't want to dig it out, you can spot-treat the plant using a weedkiller such as glyphosate. Avoid spraying on a windy day and near other desirable plants.
