Help me keep this plant alive!
By Oidara
United Kingdom 
Hello everyone.
I posted a while back asking for advice on a shrub to plant as a memorial to a little baby I lost in July to a miscarriage. You were all very helpful - thank you.
I ended up buying a shrub and several flowers to put in a large planter. The flowers are doing fine, but I am worried about the shrub!
It is a Penstemon (Phoenix Red). Since planting it one week ago, about 15 of the flower heads have fallen off. There are new buds ready to flower, but all of them as well as the existing ones have a sort of chalky white coating. Is this a sign of a problem? Or is it normal to lose so many flower heads after planting? As you can tell, I am a clueless gardener! Any advice on how to stop this plant from dying would be much appreciated.
15 Aug, 2017
Answers
Thanks for your reply.
I looked into powdery mildew, but the information I found implied that this is usually also on the leaves. In our case, it is only on the flowers.
The lady at the garden centre didn't mention needing to bring it indoors. It is labelled as being a "hardy perennial" and we did explain our plans for it, so I hope it will be okay!
15 Aug, 2017
Maybe it depends on where you live. Penstemons do overwinter here in West Wales - though how they would fare in a very cold one would probably be something else.
They seem to tend to not be very long lived but you can keep them going with cuttings as they root easily.
15 Aug, 2017
some of my penstemons have this 'floury' coating and it is nothing to worry about.
as said it is an herbaceous perennial and in a hard winter will die back and possibly die too. I always take cuttings from mine and keep them frost free to serve as an 'insurance policy'.
15 Aug, 2017
Thanks for the additional replies. I am in Devon, so not very tough winters (just very wet!).
So do I not need to do anything about this coating?
Is it normal to have lost so many flowers from repotting? There are new buds on the way, so perhaps it was just time for those to fall anyway?
16 Aug, 2017
the floury coating is fine, leave it alone. they regularly drop flowers and new ones emerge. each flower lasts a week to a fortnight , die and drop off to be replaced by new ones regularly. This is what you are seeing so perfectly natural for the plant. you could dead head ie cut off the fully spent flower stem when all the flowers are over. this will encourage new flowers to form.
16 Aug, 2017
Sorry, I thought you were saying it was all over the plant, not just on the buds - agree, not a problem.
16 Aug, 2017
Previous question
« do i cut back iris after flowering or allow the seed pod to grow?
Looks like powdery mildew - you can try the milk spray, which is 1 or 2 parts cow's milk mixed with 9 or 8 parts water, spray thoroughly, repeat as necessary, or you can try a fungicidal spray which treats powdery mildew, BUT, if you spray the flowers with a fungicide, do it at the end of the day, once the bees and other insects have stopped working.
I'm sorry to have to tell you that Penstemon are not shrubs - most are tender perennials which, if they are to survive the winter, need to be brought into a greenhouse or conservatory before the first frosts.
15 Aug, 2017