West Sussex,
United Kingdom 
I found myself unable to resist 2 erodium plants today at the nursery. One is Stork's Bishop and the other is a bit smaller in leaf and flower. This is a new plant to me. Also, the label says they like an alkaline soil and I have thick clay. Should I get a special compost or add something to their soil? Should I keep them in a cold porch this winter rather than outside? Thanks.
9 Sep, 2018
Answers
Thank you SBG. I have never seen them before but they are so exquisite, both in leaf and flower. You've given me some hope that they will survive. It was only after I got home I saw that 'Hardiness' on the label was followed by a question mark, but as you are in the north and I'm in Sussex, I expect they'll be fine.
10 Sep, 2018
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They are usually fully hardy, mine came through the 2 horrendous winters 2010/11 & 2011/12.
I'm on chalk so I am alkaline.
I'd be inclined to add some grit to the clay to open it up and improve the drainage rather than try to alter the pH of your soil. mix in some John Innes type soil may help too.
10 Sep, 2018