Whorled Tickseed ‘Zagreb’ (Coreopsis verticillata ‘Zagreb’) is a compact cultivar of threadleaf coreopsis (Coreopsis verticillata). The cultivar name references the Croatian capital. Its bright yellow flowers grow in clumps and feature darker centers. These plants are undemanding and prefer drier soils; if left in wetter conditions, they may experience crown rot.
I. Appearance and Characteristics
An excellent performer, award-winner Coreopsis verticillata ‘Zagreb’ (Threadleaf Coreopsis) is a compact perennial forming a gorgeous mound of finely divided leaves. Blooming continuously from early to late summer, it gets covered with a profusion of bright golden-yellow blossoms. The airy clumps of fine, threadlike foliage on upright stems add a lovely delicate texture element to the landscape. Long-lived, this is one of the best and toughest performers suitable for a sunny position in the garden.
II. How to Grow and Care
Sunlight
Whorled tickseed ‘Zagreb’ requires sufficient sunlight and prefers direct sunlight, so it is good for sunny gardens or balconies. To grow indoors, at least 6 hours of sunlight is needed. For maximum blooming, over 12 hours of sunlight is best.
Whorled tickseed ‘Zagreb’ can survive in partially-shaded environments. However, excessive shade can result in decreased photosynthetic rate, slow growth rate, produce thin, weak stems, difficulty in branching, and fewer flowers. Your plant will be healthier in a bright place.
Temperature
Whorled tickseed ‘Zagreb’ grows on grasslands or plains with a very dry environment. It likes a warm and dry growing environment, though it tolerates occasional wet weather. It grows best between 10 to 30 ℃. Cold temperatures result in slow growth. Sufficient water is required during germination, but adult plants have no special requirement for humidity.
Watering
Thriving in its native sunny meadows, whorled tickseed ‘Zagreb’ is well-adapted to cope with periods of drought, thanks to its deep-rooting system that allows efficient water uptake. Its preference for a well-drained environment aligns with its moderate need for moisture, necessitating watering every week to maintain a healthy balance. Given its resilience and adaptability, whorled tickseed ‘Zagreb’ flourishes best outdoors where it can fully embrace the natural rainfall patterns. This herbaceous perennial demonstrates vigorous growth during the growing season, relying on consistent but not excessive watering to sustain its vibrant flowering display.
Soil
Whorled tickseed ‘Zagreb’ adapts to most soil; some varieties even tolerate dry and rocky soil. However, it prefers moist, loose, permeable, well-drained sandy loam, with a pH value of 5.5-6.5. Add a permeable and loose medium, such as sphagnum moss and coco coir, to garden soil and organic matter to increase water retention. An example of a culture medium formula is 1/2 coco coir + 1/4 garden soil + 1/4 vermiculite or river sand. NPK fertilizer and organic fertilizer should be added in spring.
Fertilizing
To support robust growth and vibrant blooms in whorled tickseed ‘Zagreb’, fertilizing in spring with a balanced granular fertilizer is optimal. Recommended application is once monthly during active growth. Benefits include improved health and flourishing blossoms. Use caution: over-fertilizing can lead to foliage at the expense of flowers. Seasonal adjustments in fertilization are key; reduce frequency in fall and cease in winter as growth slows. For best results, apply around the plant’s drip line and water well to aid absorption and prevent root burn.
Planting Instructions
Plant whorled tickseed ‘Zagreb’ in spring or fall; in subsequent years, rely on natural seeding. Its natural seeding range is 30 to 61 cm, and its lifespan is three to five years. When it starts to bloom less, its life is ending, and it should be replaced with new plants. Sow indoors 4-6 weeks before the last frost. The germination temperature should be 16 to 25 ℃.
During germination, the medium should kept moist and the air humidity should be kept at 90%-95%, and then gradually reduced after germination. Germination takes four to six days. When two or three true leaves grow out, transplant to garden or pot. After transplanting, water thoroughly to keep the root system and soil in close contact. The whole seedling period takes 4-5 weeks, and 13-15 weeks are needed from sowing to blooming.
Pruning
Whorled tickseed ‘Zagreb’ rarely needs to be pruned. In order to promote blooming, prune the terminal bud when it grows to 5 cm. The same should be done again when branches are 10 cm long; remove thin or weak branchlets then too. Pruning withered flowers in time avoids consuming excessive nutrients, and whorled tickseed ‘Zagreb’ will bloom again in fall.
Propagation
Whorled tickseed ‘Zagreb’ is an herbaceous perennial that thrives in well-drained soil and full sun. For successful propagation, cuttings should be taken from healthy, non-flowering stems. Use sharp, clean tools to make the cuttings, which should include several sets of leaves. Dip the cut end in rooting hormone powder to foster root development and plant in a soilless potting mix. Maintain consistent moisture and provide indirect light until roots establish, after which whorled tickseed ‘Zagreb’ can be transplanted to its final location.
Transplanting
Whorled tickseed ‘Zagreb’ thrives when transplanted during the mild climate of early to mid-spring or mid to late fall. Choose a sunny location with well-drained soil for best results. Ensure consistent moisture post-transplant for swift establishment.
Pests and Diseases
Easy to grow, relatively pest and disease free, this Coreopsis is a favorite of bees and butterflies but is ignored by deer.
III. Uses and Benefits
Very versatile, Whorled tickseed ‘Zagreb’ is a welcomed addition to borders, naturalized areas, cottage gardens and does great in containers. Effective as an accent plant and spectacular in mass plantings.
IV. Harvesting and Storage
Generally speaking, whorled tickseed ‘Zagreb’ can bloom twice a year, once in spring or summer and once in fall. Its flowers can be appreciated for a long time. If it is not harvested, it can bloom as long as one or two months. After harvest, the vase life of single flower is between three and seven days. Use sharp gardening scissors to cut at the base of the stem, and prune the base of the stem obliquely at 45° to increase the water absorption area. Put it in a vase with clean water.
