Is there a white knapweed?

[Margaret]

I have been turning an area of rough ground into a place with bee and butterfly friendly plants. At this time of year it is mostly knapweed. Today I noticed that one of the plants is white. Has anyone seen this elsewhere?

[mark smyth]

wow its lovely.

I used to have one called Silver Halo where the outer florets were white

[Alan_b]

There literally is a White Knapweed, Centaurea diffusa http://en.wikipedia.org/wiki/Centaurea_diffusa but yours is a white form of (I think) Centaurea nigra.  The second picture down on the right here appears to show a white form http://wildseed.co.uk/species/view/32 .

The RHS Plant finder list two suppliers of Centaurea nigra var. alba.  If it were me, I would take this plant under my wing and cultivate it as something out of the ordinary.

[Maggi Young]

I haven't seen a pretty white form like that, Margaret. What a special bee friendly plant that will be - lucky you!

[Margaret]

I hope it is a white form of Centaurea nigra and not C diffusa which sounds like a baddie.  How should I go about collecting seed of the white form given that it's surrounded by a sea of its lavender relations.

[mark smyth]

what happened to your plant?

[Brian Ellis]

I hope it is a white form of Centaurea nigra and not C diffusa which sounds like a baddie.  How should I go about collecting seed of the white form given that it's surrounded by a sea of its lavender relations.

If it's centaurea and you can get to the roots it will easily make new plants, much quicker than seed.

[ian mcdonald]

Hello Margaret, quite a few of our native flowers have white forms naturally. White bluebells, white basil, white marsh thistle, white heather, white bell heather etc.

[Margaret]

Hi Mark, Brian and Ian

Sorry not to have replied before. I had had a bad year or more and didn't follow the forum or do much gardening. When I started reading the forum again I never thought to look at 'new replies to your posts' because I hadn't made any!

The white knapweed is doing fine along with all its purple friends. In fact they are all growing a bit too well and have started seeding into the flower beds. My brother-in-law complained about the area (about 3 x 15m) looking a mess last summer. I was upset at the time but I'm starting to wonder if Centaurea nigra was a mistake. It likes the conditions (rich loam on a sunny cliff top) a bit too much.  I'm thinking of taking out a fair sized junk (not the white though) and trialing a few other things. Maybe Centaurea scabiosa would be better behaved.

Can anyone suggest plants for growing in rough grass on good soil? The yellow rattle (Rhinanthus minor) which was planted 4 years ago did nothing to weaken the grass and has disappeared. The grass is not mown because of Spring bulbs, mostly Pheasant Eye daffodils and a few Camassia.

Many thanks for the help with the white  knapweed.

Margaret

[Tristan_He]

Lovely plant Margaret, will you be donating seed to the seed exchange?

I've not found yellow rattle easy to establish either - perhaps the wrong sort of grasses. I have instead invested in an Austrian scythe which is very effective for managing long grass (and the perennial border when things need cutting). See http://www.thescytheshop.co.uk/

Personally I'm very fond of small scabious (Scabiosa columbaria) - it's also a very good bee and butterfly plant and would look great with the knapweed. The related S. ochroleuca is nice and a pleasant creamy colour (not native though if this is important to you). I wouldn't recommend Centaurea scabiosa as this tends to be larger and more aggressive than C. nigra.

Tristan

[mark smyth]

To establish yellow rattle I think you need to cut the grass down to soil levels scarify the ground and sow the rattle seeds

Here's a white marsh thistle on Jo Hynes land. Saw it late at night which is why the flower is in my hand

Also saw lots of white rosebay willow herb on the roadsides in England. I'd give that plant a home

[Brian Ellis]

Also saw lots of white rosebay willow herb on the roadsides in England. I'd give that plant a home

I did, it is said that it is sterile so you may think you are safe, but it spreads by underground stolons (rather too well in my border) and I spend a lot of time getting rid of it down to a manageable size again.  If you want a runner Mark....

[Tristan_He]

Yes, rosebay willow herb is a terrible weed. Avoid!

I've tried scarifying the soil, cutting back turf really hard, sowing together with grass seed, mixing with sand.... all sorts. Just doesn't seem to get going. The frustrating thing is that there is loads of it in the meadow next door (and yes I have tried seed from there, with permission)!

May try some Euphrasia instead.

[Neil]

Read this about establishing yellow rattle http://wildseed.co.uk/page/using-yellow-rattle-to-increase-species-diversity  it did take me a couple of years to get it established. 

[Tristan_He]

Thanks Neil, that's a useful link. I will keep trying.

Tristan