Electric Blues - Corydalis for shade

Electric Blues…

This is the time of year that the new foliage of the various blue flowered woodland Corydalis starts to look like it will become more than just a tuft of leaves, and actually produce some flowers.  Although some of these blue species have been grown in gardens in Europe and America for many years it wasn’t until the 1992 collection of three forms of Corydalis flexuosa from China under the CD&R 528 code (Compton, D’Arcy and Rix) that they became more available to gardeners.  Since then more forms have been introduced from the wild and various garden hybrids have been named.

As often happens with new plants to cultivation there have been some confusions over the correct identity of some forms and it seems that more species have been introduced to western gardens than it at first appeared.  The two main species we will encounter are the above mentioned, Corydalis flexuosa, and the taller, scented and slightly later flowering Corydalis elata.  Others that are (or may be) involved in the hybrids in cultivation include Corydalis cashmeriana, Corydalis curviflora and others yet to be identified or named.

The original three forms of Corydalis flexuosa were given cultivar names to excuse us from having to use the codes; ‘China Blue’, ‘Pere David’ and ‘Purple Leaf’.  All are low growing (up to 20cm usually) and slowly spread to form patches of their finely cut foliage and bright flowers, usually becoming dormant in the heat of summer before reappearing in late autumn.  ‘Purple Leaf’ unsurprisingly has distinct red-purple markings in the centres of the leaves and the flower buds are purplish.  The other two have slightly glaucous, olive green foliage.  All three open flowers to an unlikely bright electric blue in April and May.

Corydalis elata has been grown in gardens for many years but the ordinary form of the species seems to be less than easily grown, or at least it is here in East Anglia!  Fortunately I obtained, from the late Alan Bloom’s Dell Garden, a selected form called ‘Blue Summit’ some years ago which has proved to be much more amenable to cultivation and indeed hardy and easy.  Brighter, fresh green foliage than Corydalis flexuosa, red flushed stems and generous heads of rich, gentian, blue flowers in May and June.  Corydalis elata is much less likely to be summer dormant and therefore easier to grow in the garden as it doesn’t cause gardeners new to these Corydalis to think that it has died mid-season.

More forms of Corydalis flexuosa have appeared, notably Corydalis flexuosa ‘Balang Mist’ which was introduced by Christopher Grey-Wilson and is the most beautiful white with a blue flush.  Unfortunately ‘Balang Mist’ has proved impossible to keep for me in Norfolk.  ‘Blue Panda’ and it’s yellow leafed variant ‘Golden Panda’ are supposed to be forms of Corydalis flexuosa but they seem quite different to my eye and are much smaller growing, with differently shaped flowers.

Corydalis flexuosa Norman’s Seedling and ‘Hale Cat’ are others which I’ve found over the years, both slightly different to other forms but it can start to get like Geranium and Aquilegia where every seedling is a little different, but are they all worth naming?

Of more interest may be some of the hybrids.  Usually described as Corydalis elata x Corydalis flexuosa, at least some of them are likely to involve other species such as Corydalis curviflora.

Corydalis ‘Spinners’ was the first one that I obtained and have now grown for over 10 years.  I can happily say that it is probably the most vigorous and reliable of all these blue Corydalis, not that it is rampant of course!  It is a clump former with the fresh green leaves and reddish stem of Corydalis elata, topped with large heads of bright electric-gentian blue flowers from amethyst buds to 75cm or so (in good conditions, 30cm in poorer soils), the rich honey scent can almost be overwhelming if the flowers are picked and taken into a vase where they have a good life.  Flowers from May to July given enough moisture and no really hot weather.

Corydalis ‘Tory MP’ is similar to ‘Spinners’ but tends to be a little smaller to perhaps 50cm.  I haven’t noticed any scent from it but perhaps ‘Spinners’ has been masking it!

Corydalis ‘Craigton Blue’ has come to us from Scotland and looks and grows much like a form of Corydalis flexuosa, low growing, slowly spreading clumps/patches with flowers of a lighter but still bright blue.

Corydalis ‘Kingfisher’ is another hybrid like ‘Spinners’ and ‘Tory MP’ but has a reputation for being difficult and I have yet to try it.  It does perhaps have a better name than some…

There are plenty of others out there, I have recently obtained ‘Rainier Blue’ named by Dan Hinckley, ‘Wildside Blue’ from Keith Wiley and Corydalis curviflora ‘Blue Heron’ to try out and propagate in due course!

Bearing in mind that these are Chinese woodland species, all of these Corydalis will do best in a good, leafy, drained soil that does not dry out, in at least dappled shade.  The forms and hybrids of Corydalis elata tend to be easier if you have had problems with others and they are remarkably tolerant of less than ideal conditions.  I have found that they also make excellent container plants in a good compost in a shady site.

For more information please see the Corydalis section of our shop here.

(c) Tim Fuller, March 2015