Carolina larkspur (Delphinium carolinianum) prefers well-drained areas, so horticulturists who wish to grow it must take care in their watering scheme. Carolina larkspur is toxic to humans if ingested, but it’s a favorite of slugs, which can destroy the plant quite rapidly.
I. Appearance and Characteristics
Delphinium carolinianum, commonly known as Carolina larkspur, is a species of perennial flowering plant in the buttercup family. It is native to central and eastern North America, where it is found in prairies and rocky glades. It produces blue to white flowers in the spring.
Each plant features a basal cluster of long-petioled, grayish-green leaves (to 4” wide), each leaf being palmately cleft into five deeply cut lobes with each lobe being further divided into 2-3 secondary lobes.
A sparsely-leaved flowering stalk clad with small alternate leaves and topped by a stately terminal spire typically containing 6-14 blue-violet spurred flowers rising from the basal leaf cluster in an April-May bloom which occurs at a time when the flower stalk has risen to about 12” tall. Plants continue to grow upward after bloom, eventually reaching 18-24” tall.
Each flower (to 1 1/2” long) has five petal-like sepals and four petals. Sepals are usually violet blue to purple, but sometimes variegated with white. The upper sepal of each flower forms a long upright backward projecting spur as described by the common name of larkspur. The four petals are very small. Fruit is a seedpod which separates into 3 parts, with the dried ends extending upward in a manner reminiscent of horns.
Four subspecies have been named:
- Delphinium carolinianum var. calciphilum – Native to cedar glades of the Southeastern United States
- Delphinium carolinianum var. carolinianum – Widespread in central and eastern North America
- Delphinium carolinianum var. vimineum – Native to coastal areas of the United States and Mexico
- Delphinium carolinianum var. virescens – Native to the Central United States
II. How to Grow and Care
Carolina larkspur is a perennial species that thrives in temperate climates with full sun to partial shade and requires well-drained soil. Special care points for carolina larkspur include regular watering while being cautious of overwatering, and support for tall stems during the growing season. Carolina larkspur’s susceptibility to pests and diseases, like powdery mildew, increases its care difficulty to a moderate level; attentiveness to these challenges is crucial for its successful cultivation.
Sunlight
Carolina larkspur flourishes in conditions with partial sun exposure as its ideal light environment, benefiting from a balance of sunlight and shade. In its optimal setting, Carolina larkspur enjoys bright light for part of the day but is shielded from the harshest afternoon rays, which can be too intense. While carolina larkspur possesses a degree of adaptability and can tolerate full sun exposure, it is imperative to note that such intense conditions may lead to excess stress, risking growth inhibition and potential leaf scorch. These factors make carolina larkspur a versatile candidate for outdoor gardens, thriving best in areas that offer morning light and afternoon protection. The plant’s adaptability to light exposure signifies its resilience and the potential for a broad range of landscape uses.
Temperature
Carolina larkspur requires cool summer conditions for proper growth and does not do well in hot, humid conditions (except for a few exceptional hybrids). Flowering can be induced by the day-night temperatures between 2 to 16 ℃. Growth and flowering requires constant moisture, so water carolina larkspur at least weekly. More caution should be observed during dry summer periods.
Watering
Thriving in its native habitat’s moisture-rich environments, carolina larkspur has adapted to require consistent hydration. This species exhibits a preference for regular watering, aligning with its natural predilection for steady moisture levels. As such, it benefits from watering every week to maintain its health and vigor. In domestic settings, carolina larkspur is more commonly grown outdoors where it can mirror the water availability of its natural setting. Given that carolina larkspur is an herbaceous plant, maintaining soil moisture is crucial during its active growing season to support robust growth and flowering.
Soil
Carolina larkspur needs humus-rich, well-drained, moist soil for proper growth. Seeds will germinate in these optimum soil conditions. Start plants in plug trays having soil with sterilized peat moss, perlite, and vermiculite at ratios of 1:1:3 or 2:0:3, and with a pH of 5.5-6.5. Keep soil wet until roots are established.
Prepare the garden site by adding a foot-deep layer of compost and digging a hole twice the diameter of the pot. While backfilling the hole, the root ball of the plant should be level with the surface of the soil. Applying organic fertilizers to the soil and using grit can help prepare soil for carolina larkspur.
Fertilizing
For optimal growth, carolina larkspur benefits from a balanced fertilizer, such as a 10-10-10 formula, applied once at the start of the growing season to support vigorous growth and once just before flowering to enhance bloom production. Use fertilizer sparingly, as over-fertilization can be detrimental. During the active growth phase in spring and summer, carolina larkspur may require monthly fertilization, with a reduction in frequency as the plant enters dormancy in fall and winter. Always water carolina larkspur thoroughly after fertilizing to distribute nutrients and prevent root burn. For accurate dosage, follow the manufacturer’s instructions.
Planting Instructions
Sow carolina larkspur in early spring or early fall. Start seedlings indoors in plug trays. For seeds to germinate, water, fertilizer, and temperature must be consistent. Pre-cool seeds at 7 ℃ to increase germination; then keep them at 16 to 20 ℃. It’s germination will take 5 to 6 weeks.
After germination, keep the temperature around 25 ℃ during the day and 16 ℃ at night until 1 or 2 true leaves emerge, and then 10 ℃ at night to avoid premature flowering. Young plants can be taken to the garden for fall planting 5-6 weeks from the emergence of root or germ. Plant seedlings 46 to 61 cm apart.
Pruning
For best flowering, prune new plants to 2-3 spikes per plant, or 5 to 7 spikes per plant in established plants. Once the flowers wither, cut the spike to the size of the smaller shoots of the plant for a second round of flowers in late summer or early autumn. Once the plant wilts in the autumn, prune it completely to the ground.
Propagation
Carolina larkspur can be effectively propagated through sowing. Begin by collecting healthy seeds from mature plants. Prepare a well-draining growing medium that retains moisture but does not become waterlogged. Sow the seeds at the correct depth, lightly cover with soil, and maintain a consistent moisture level. Ensure the seeds receive adequate but indirect light to encourage germination. Once seedlings develop true leaves and reach a robust size, transplant them to individual pots or their final growing location, caring for them as they establish.
Transplanting
For carolina larkspur, the quintessential window for relocating is from the awakening till the zenith of spring, ensuring roots establish before summer. Choose sunny spots with rich soil. Gentle handling of delicate roots ensures successful resettlement.
III. Harvesting and Storage
During peak summer months, carolina larkspur flowers can be harvested for ornamental uses. Use sharp gardening scissors to cut at the base of the scape (or stalk), and prune the base of the flower branch obliquely at 45° to increase the water absorption area. Arrange in a vase with clean water promptly.
