Unsure if plants are dead
By Ads2k15
West Midlands,
United Kingdom 
Last year I planted a couple of new garden borders, but am now unsure if the following plants have died over winter:
1) Rudbeckia sullivantii 'goldsturm'
2) Cosmos atrosanguineus Chocamocha ('Thomocha')
3) Geranium 'Brookside' cranesbill
The rest of the plants in these borders seem fine and have sprung new growth recently as the weather has begun warming up and we've had more sun. The geranium has completely disappeared, am unsure if it's meant to die back and then reappear in spring? The other two just have some twigs with no leaves on. All were protected with mulch over winter and I put a plastic cloche over the cosmos.
Any suggestions on how I can tell if they are dead or not or how long I should wait before replacing them to give them a chance of sprouting new growth?
21 Mar, 2015
Answers
Although most herbaceous are showing signs of waking up, it's still a bit early. I have a few young autumn planted perennials (i hate planting in autumn then letting the plants sit there in cold wet soil all winter) and they're still dormant. A little careful scratching below the surface of the soil might reveal life.
22 Mar, 2015
Its been so cold recently the plants in my garden are struggling to wake up, the hardy geraniums hardly have a leaf between them but give them a chance and wait for warmer weather, when they do wake up a spring feed wouldn't hurt.
22 Mar, 2015
The Cosmos may not reappear - this particular one isn't hardy other than in, if you're lucky, the mildest of winters in an extremely sheltered, warm spot. RHS advice is to lift and move to a greenhouse or somewhere frost free for winter. The other two plants are fully hardy, so it may be the Cosmos you're not seeing, and the dead stuff represents the other two plants.
22 Mar, 2015
Interesting.
I also grew a Geranium 'Brookside' for the first time last year and it flowered well. But in December it totally disappeared. At present there is no sign of it either and carefully scratching away around the area it was planted there appears no trace of it left. Not even the crown. It looks like it rotted away over winter. I've never had a geranium die on me before and I've grown them for years.
I have another geranium 'Blokovo in the same bed also planted at the same time as 'Brookside' and that's already sprung back into life.
Let us know if yours ever comes back.
22 Mar, 2015
Hmm, well now that's intriguing Bendipa - if Ads2k15's 'Brookside', doesn't reappear, and yours doesn't either, that might mean its a lot fussier than the older varieties - it's a fairly recent introduction. Hopefully, it's just a late starter in spring...
22 Mar, 2015
My G. Brookside is just showing the slightest signs of life and I really do mean slightest! I was a bit worried about it too but over the last two sunny days it has started to wake up.
22 Mar, 2015
Well hopefully, that means its just a late starter!
23 Mar, 2015
Many plants are still asleep. Unlike last year, it's going to be a late spring I think.
23 Mar, 2015
At last. My Geranium Brookside has come to life. And I really thought it was a gonner. So this variety IS a late starter. Be warned. When it dies back in early winter it seems to leave no trace of itself. So one can be forgiven for thinking that it had rotted away.
26 Mar, 2015
Belated thanks for your responses. I lost my Cosmos so will have to think of something else that's more hardy to put there. The other plants pulled through and are flowering nicely at the moment.
3 Aug, 2015
The rudbeckia and cranesbill should be fine. All the top growth can be cut off the rudbeckia, and it will grow again once it has warmed up a bit. As for the cosmos - wait and see. It's too early to see any signs from it yet.
21 Mar, 2015