Threadleaf is a common name for Coreopsis verticillata, a common North American wildflower belonging to the Asteraceae family. Its name refers to the plant's very finely divided, threadlike leaves. The bright yellow or pink flowers of these herbaceous plants are similar in form to daisies. They are also called tickseed, for their tiny seeds that somewhat resemble ticks. These plants flower all summer and will continue to produce a few flowers well into autumn.
All varieties of threadleaf are true sun lovers and will tolerate extreme heat better than just about any other perennial. They will grow in virtually any type of soil, as long as it has good drainage. Threadleaf plants are very hardy and easy to grow, making them good plants for beginning gardeners. They are perfect for new gardens, because they rapidly grow into 2-foot-tall (61-cm-tall), bushy plants with swarms of flowers.
Flowers of these garden plants should be removed as they fade. If they are allowed to go to seed, the seeds will scatter everywhere and produce countless little threadleaf seedlings. Deadheading keeps these plants within their boundaries and encourages them to keep producing new flower buds. It also keeps them from becoming leggy and spindly, and increases bushiness.
It is easy to propagate these herbaceous plants by seed or division. Seeds usually sprout within a week and will bloom in just two or three months. Mature plants can be divided in spring, or cuttings can be taken and planted directly in the garden. Small tufts of new growth will appear in late summer around the base of older plants. If these small rosettes are cut and planted in moist soil, they will quickly develop roots and grow into new plants.
Threadleaf coreopsis has the misfortune of being very vulnerable to insect damage, mainly from aphids and cucumber beetles. While aphids are fairly easy to eliminate with a strong spray of water, cucumber beetles can be more persistent. It may be necessary to use an insecticide to get rid of them. The plants are also prone to diseases such as rots and fungi, especially in areas with a lot of rainfall. Growing these plants in areas with good air circulation and plenty of sunshine can help to prevent disease.
Threadleaf flowers are good for cutting and will stay fresh in a vase for days. Many gardeners find they look nice combined with sunflowers, black-eyed Susans and daisies, as well as many other wildflowers. They are one of the best plants for butterfly gardens, attracting several types of small butterflies. Many types of songbirds are also attracted to these plants and feed on the seeds.