cephalaria gigantea

Margaret657

I have had this in my herbaceous border for 5 years. I have loved the flowers and they have been admired by many but help. I now discover the "clumps" have grown and grown and taken over a huge area of my border. the "roots are very deep and very hard to dig out. I am on clay soil and worried that these are spread by underground tubers, rhizomes which easily break off.  be warned. pretty flowers but very invasive after a time

Paul B3

The 'giant yellow-scabious' is a stunning perennial for the back of a large border . My own soil is quite a light but good loam ; this plants roots would pose problems on a clay soil .

I don't think it spreads by rhizomes , just very powerful roots ! Deep digging to extract them is the only alternative .

Think I may be answering a question here that you havn't even asked , ; but your point regarding this species is entirely justified ; a warning worth heeding indeed .

Dovefromabove

Large established plants have large established roots ... but I wouldn't call that invasive. 

Paul B3

Muddle-Up

Your garden looks very nice indeed ! Can't beat 'natural planting' .

Obelixx

The clue is in the name - gigantea.   It isn't invasive particularly but it does increase the girth of its base every year - good for getting offsets if you lift and divide now and again - and produces lovely tall, airy stems of flowers.   it also will self seed and have babies if happy.  Mine did.   Loved it and hust hope the seeds I saved for this new garden will be happy here.