Corydalis is a welcome gem in the spring garden. Its spreading ferny foliage hugs the ground, sprouting little pink, red, yellow or clear crystal blue flowers.

Three-quarters of the 450 or so species hail from the mountains of China and Tibet. But many Corydalis solida forms occur naturally in northern and central Europe.

So you can imagine my delight when I came across one while walking in a Swiss beech wood a few years ago.

We should often try to mirror a plant’s natural growing conditions in our gardens. Corydalis solida, a popular choice for gardeners, needs moist, very free-draining and slightly shady conditions.

Believe it or not, it loves our cool, cloudy summers and can be much more challenging in the hot, dry conditions gardeners in the south of England have to endure.

With solid tuberous roots, this species is one of the two main groups in the genus. And, if you’re looking for a tough, easy-going solida, “Beth Evans” is your plant. Delicate pink-spurred flowers grow no more than 15cm above their ferny carpet.

This variety is named after Beth, the wife of Alf Evans, an alpine specialist at the Royal Botanic Garden Edinburgh, and it was almost certainly bred from a seedling in the Botanics.

After a fine spring display, the plant dies back completely and, unlike many other flowers, doesn’t leave a horrible tangle of decaying foliage. You’ve then got space for later flowering neighbours such as hostas or hardy geraniums to take over, and as they die back in winter they won’t compete with the corydalis.

I’m not surprised that C flexuosa is a widely-grown fibrous rooted corydalis, and certainly wouldn’t be without my ever-spreading little clump of strongly scented “China Blue”. It’s perfectly placed close to a willow arbour I planted several years ago – right beside one of our favourite sitting areas.

With luck, it won’t be snowing when these charming little clumps of clear electric blue flowers emerge. The bronzy shade of foliage should gradually green up as the spring progresses.

We normally associate bees with flat headed flowers, but these tuberous flowers are indispensable to queen bumblebees coming out of hibernation. Corydalis have developed a slightly unusual technique for their visitors. C cava, a native of southern Europe that can sometimes be seen in the UK, has four petals, with two outer ones curved outwards. The larger upper petal has a spur containing nectar.

The two inner petals close together at the tip and as a bee lands on the lower one, the upper is triggered to open. This lets the bee enter and get covered with pollen as it pushes down the long narrow tube towards the nectar.

The flowers are self-incompatible, so pollination must be between two plants. Unless only one variety is grown within a bee’s range, the resulting hybridisation must produce a random collection of flower shades and colours. So expect anything if you allow self-seeding and ruthlessly remove any plants that don’t conform to your colour scheme.

Unfortunately some nurseries, I’m sure unwittingly, may sell tubers that aren’t true to their supposed parent. The green pods that fall close to the parent could easily be a cross, so a tuber grown from that seed wouldn’t breed true. You could have much more wishy-washy shades than you had expected.

And, just to make matters worse, catalogue photos of any one variety can vary hugely, as does the quality of the published picture. The only completely safe option is to buy a plant when in flower, remembering that flowers, especially red forms, are often darker after a cold winter like this.