The hollowroot-birthwort enchants with dainty carpets of leaves, above which fragrant flowers in white and dark violet pink open.
Profile of hollowroot-birthwort:
Scientific name: Corydalis cava
Plant family: poppy family (Papaveraceae), subfamily fumitory family (Fumarioideae)
Other names: –
Planting time: spring, but best in autumn
Flowering period: March to April
Location: semi-shady to shady
Soil quality: sandy to loamy, calcipholous, nutrient rich, humus rich
These information are for temperate climate!
Use in: underplanting, overgrowth, natural garden, forest garden
Winter hardiness: hardy, USDA Plant Hardiness Zones: 6 (-23 °C / -5 °F)
Bee and insect friendly: Yes
Plant characteristics and classification of hollowroot-birthwort
Plant order, origin and occurrence of hollowroot-birthwort
The hollowroot-birthwort belongs to the fumitory family (Fumarioideae). Botanically it is called Corydalis cava, which is derived from the flower shape (Greek “korydalis” = crested lark) and the hollow tuber (Greek “cava” = hollow). Its natural locations are closely related to beech forests, so the plants are mainly found in Central Europe, but are absent in low-lime or lime-free locations. In southern Scandinavia and the British Isles, the hollowroot-birthwort has now been eascaped from the gardens. Almost all parts of the plant are slightly toxic, only the tuber is considered to be highly toxic.
Characteristics of hollowroot-birthwort
The hollowroot-birthwort is a perennial, herbaceous perennial that – depending on the location – can reach a height of 15 to 30 centimeters (6 to 12 in). Every spring new, unbranched and hairless shoots sprout from the hollow tuber. Over the years, one or two tubers, of which the plants can spread and quickly form lush polster. Soon after the seeds ripened in May the aerial parts of the plants withdraw.
The hairless, double-three-part and incised leaves are colored blue-green and alternately sit on the stem.
From around March and until April, Corydalis cava opens its white to violet or dark pink, slightly fragrant flowers, with the upper petal ending in a long, curved spur. The lower bract is undivided, which makes it easy to distinguish the plants from the closely related fumewort (Corydalis solida). Each individual flower is only 2 to 3 centimeters (0.8 to 1.2 in) long, but 10 to 20 of them sit together in racemose inflorescences.
Pale green capsule fruits develop from the blossoms, which tend to tilt downwards as they mature. These capsules open in May and the shiny black seeds drop out.
Hollowroot-birthwort – cultivation and care
The hollowroot-birthwort prefers semi-shady to shady places, often in connection with deciduous trees, but sometimes it also spreads to sunnier locations.
Moist, permeable and humus-rich soils with clay content are ideal. They should also be rather nutritious and calcareous. The hollowroot-birthwort is happy about a layer of mulch.
You can plant Corydalis cava from spring to autumn, with autumn being the best time. Keep a distance of 20 to 30 centimeters (8 to 12 in) from the neighboring plants. The tubers are also commercially available, which are placed 5 centimeters (2 in) deep in the ground and at a distance of at least 10 centimeters (4 in) from each other.
Water less often, but thoroughly and penetratingly and let the soil dry in the meantime. This stimulates the plant roots to grow into the deeper layers of the soil, which means they survive dry periods better.
With a sufficient humus layer, no fertilization is necessary for Corydalis cava, otherwise an amount of fertilizer in spring at flowering time is recommended. Suitable or this is compost or a layer of mulch and leaves.
The hollowroot-birthwort is easy to maintain, especially if it is in the right location. It even reacts extremely sensitively to cultivating the soil and thus its roots. If the stocks become too large, they can be easily reduced by digging them out. If you do not want the plants to sow themselves, you must cut off the flower stems before the seeds ripen.
The plants basically propagate by their own, by seeds and by tubers. So you just have to dig up the young plants. If you want to sow, please note that lark spurs need cold to germ. The seeds first need a good six-week warming phase, then an at least as long cold period to germinate.
Diseases and pests
The hollowroot-birthwort is – at the right location – robust and healthy. Only snails can cause problems.
The hollowroot-birthwort is hardy down to -23 °C / -5 °F.
Use in the garden
Corydalis cava fits wonderfully on the edge of the wood, under fruit trees or in (half) shady beds, generally wherever it can grow undisturbed. Lenten roses (Helleborus Orientalis hybrids), liverwort (Hepatica), lungwort (Pulmonaria), blue violets (Viola odorata), wood anemones (Anemone nemorosa) and tuber flowers such as daffodils are suitable for these locations and the early flowering period. Hosta, astilbe or vinca also go well with it, especially since they cover the early gaps that the plants leave behind.