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I have some beautiful purple Raven pentstemons, but all the flowers are covered with a dusty white deposit.  It's definitely not mildew.  What causes this, and will it go away eventually?  I have some other pink penstemons and they aren't affected.

Victoria Sponge

I've got this too happycottontail- just on some flowers and not on the leaves as you say - I was ignoring it but would be interested to know what it is

We shall just have to await a visit from those who are wiser and more knowledgeable than us, V S  

I have a similar problem I think I recognise powdery mildew this looks like tiny bird poo, more lumpy than powdery...doesn't it sound disgusting ukk . 



I have the same problem, I grew these from seed I bought in the UK.  Really interested to know what it is as I too don't think it is mildew.




That's exactly what it looks like Pootler, and it definitely doesn't look like mildew.  It's as though someone has come along and covered the flowers - not the leaves - with finely sifted icing sugar.


I had a quick Google but couldn't find an answer.  Really want to know the answer now!


It looks almost like the farina you get on some auriculas - but I've never heard of penstemons with farina.

However, if you click on this link   and scroll down quite a long way, you'll find a photo of a dark penstemon (not clear if it's a Raven) with the same white markings.

Perhaps it's time to make enquiries of the RHS?

Dove, my first thought was a farina of some sort, and like pootler, I googled it but without success.  I looked at your link and those penstemons have it, but I think my Ravens are darker.  As you say, probably time to call in the experts!


i purchased a blackberry and cream penstemon (similar dark colouring to yours) yesterday from a trusted small nursery nearby. it had some of the same white specks on it and the worker said not to worry about it as it was just what the water had done to the flowers.

I would be intrigued to find out if this is true or not!

Victoria Sponge

Indeed! Because mine weren't watered for several weeks until it rained two nights ago 

That sounds nice blackberry and cream...

Just looked at my penstemons a blue and a dark one they also have a little of 

this mystery white substance on them.  could it possibly be fairy dust ? 

I also have a new one called Amelia Jane in my back garden but it's not in flower yet 

and no sign of any white stuff.


Right then, I think plan B is to take up Dove's suggestion of contacting the RHS.  I notice that at Hampton Court next week there will be an RHS stand with gardening advice for their members from the science team.  

Do we know anyone that will be attending, that is a member, that could take up our cause?!


Brilliant idea pootler!  I would love to go but have a poorly leg at the moment.


Victoria Sponge

I'm not a member or attending...politely bumping though!


my penstemons have them also my blackbird ones. bu they had it last year and its seem to be only dark ones.. so unsure why but it doesnt seem to effect the flower or anything.. just looks unsightly. it reminds me of garden centres when they water with tap water and its a residue left by limescale and that. but  not sure..

No gf, this isn't limescale residue from GC watering. My plants were bought last year and the first crop of flowers did have this white dust, but I don't think the second one did.  In Spring I cut them right down and transplanted them to a new spot in the garden, where they are doing exceptionally well.  So all the current flowers have never seen a nursery and have only been watered with rainwater.

GUESS WHAT! I was so preoccupied with the Tour de France up here in Yorkshire over the weekend that I didn't do anything in the garden - didn't even go for a walk round it.  But this morning I was out there, and lo and behold, the dust had vanished from the penstemons!!    Was it the heavy rainfall on Friday night that cleared it away?  Am wondering if those of you who had the white dust problem still have it?

Victoria Sponge

Hi HCT, ( if I can call you that?)

Mine seemed to be at its worst before this thread started and was already easing. There is still residue around the buds and unopened flowers, but just tiny amounts.

Ive got some very young/small penstemons that probably won't flower 'til later in the year so I'll keep an eye on them too...