Hi Phloxie, I grow all three and I also garden on chalk bedrock. All grow well in some shade in the garden and are un demanding. They will all be available in gc from march onwards in my experience. There are many different species of corydalis, some self seed freely such as C lutea [ yellow flowers] then some are very good spreaders such as the blue flowered C flexuosa. C solida come in a range of colours from pale mauve to deep red etc.
I'd buy the erythroniums in leaf rather than as a corm as I have had less success growing them from a corm.

Solomans seal is easy and when happy can become a bit of a thug though it does get attacked by a sawfly that strips the leaves.

They all prefer a moist "woodsy" soil and are happy in part shade. Good luck with them, they are all lovely. With corydalis, lutea grew rampantly for me on sandy soil but flexuosa died. Flexuosa does well here on moist neutral soil in part shade. Good to know that SBG succeeds on chalk with them.

Many thanks SBG for your very informative answer to my question. It is great to know that you grow all three of the plants I wanted to know about on the same kind of soil that I garden on. I had envisioned that I would encounter problems as I had heard that all three would only grow in woodsy conditions which I assumed as being leaf litter etc. However, I feel much more confident now about purchasing all three from the GC as and when they become available.
Many thanks also to SG for your reply which I also found very helpful.

yes steragram is right , a leaf littered soil is best and as my shade is from beech tree and hedging it does get that extra humus rich leaf litter. but if you haven't got any then dig in garden compost or compost for planting in at the time you plant them.

Hi Phloxie, I have a very healthy erythronium grown from a corm 3 years ago. I saw it smiling happily when I drew the curtains this morning and thought I ought to look it up so I could care for it properly. I just typed it into google and your question came up. I agree that it might be best to buy in leaf as I have only the one plant out of several planted, but this one is spreading into a very healthy clump with a number of blooms. It is growing on thick clay in constant shade from the garage and the spot gets very dry in summer, so I would have thought the conditions are not ideal. After reading the answers here I shall give it the leafmould I have and I shall buy some more this year. I just love them.