Knautia, a genus of plants in the Caprifoliaceae family, is commonly called crimson scabiosa and is indigenous to Central Europe. Linnaeus named the genus to honor two 17th-century botanists and physicians, Christoph and Christian Knaut.
These can be cultivated as annuals or as perennials, growing 12 – 36 inches tall and 12 – 24 inches wide and becoming fully mature in 2 – 5 years. They have interesting dark green leaves growing in rosettes at the plant’s base. The lower leaves are somewhat lobed, becoming divided as the flower stems grow higher.
They have a long flowering season from summer to autumn and produce beautiful and interesting pincushion-like 1 – 1.5-inch dark pink or deep-red flowers that are often used in bouquets. Although the pollen and nectar-rich flowers don’t last very long, deadheading old flowers encourages the plants to profusely produce new flowers. These clump-forming plants tend to flop in windy conditions.
Several breeders are working on developing newer varieties with stronger stems and more upright growth. A variegated variety has also been developed. These plants attract bees, butterflies/moths, beneficial insects, birds, and other pollinators. Flowers that aren’t deadheaded produce seeds that attract birds.
They are very flexible and can tolerate an assortment of conditions, making them good plants to cultivate by novice gardeners or those with higher skill levels. Their compact and full growth grow well in garden beds as well as in containers. Due to their floppy growth, protect them by planting them near other shrubs or close to a fence or building to shelter them from strong winds.
If provided with good growing conditions, they make excellent perennial plants for your garden. Flowers can be harvested to display in vases or added to floral bouquets without damaging the plants since they produce flowers in abundance during their flowering season.
They love growing in bright sunshine and so plant them in a spot that gets enough sunlight. They are not suitable for growing indoors as they don’t like low or artificial lighting.
These drought-tolerant plants prefer growing on average to dry soil. Watering can be kept to a minimum by watering them once in 9 days or even longer if it rains. One of the ways to kill these plants is by watering them too often or too much and drowning the plants.
However, newly planted transplants need more frequent watering until they get established, generally every 4 – 5 days. Check the soil close to the roots – if it’s totally dry, water the plants until the water reaches about 2 inches deep in the soil. This must be done once weekly during their first growing season, reducing to every 9 days for the next year.
They can’t tolerate high humidity levels. They are easily prone to get root rot under humid conditions. Reduce watering if humidity levels rise.
They do well under temperate conditions of warm days and cooler nights, tolerating temperatures down to at least -25°F. They can tolerate hot weather, but they won’t last long or look healthy. High temperature and humidity, like that of the southern areas of the US, are not suitable for growing these plants. In such conditions, the plants are likely to wilt and die.
They prefer well-draining soil of any type. The soil must be a bit damp or dry for these plants to really thrive and to avoid root rot as well. They can tolerate acidic or alkaline soil, although prefer growing in neutral or alkaline soil.
These perennials need repotting into larger containers after they double in size or once annually to refresh nutrients in the soil. They can be divided at this time if necessary.
Ease them out of their containers and transfer them into new and larger containers filled with fresh soil.
They can be either propagated by seeds, cuttings, and division. The best time to start this is in spring, around March or April.
Propagation from seed
They can easily be grown from seeds. Sow them straight in the garden or in starting trays in the spring. Once germinated, plants need hardening off before transferring them to the garden.
They are also excellent self-seeding plants and drop seeds that easily germinate without any human intervention. If you prefer to stop them from spreading, deadhead old flowers to prevent seeds from developing and remove any new plants that grow from dropped seeds.
Propagation from basal cuttings
Select a healthy actively growing stem with 1 or 2 leaves and a node and cut it off close to the soil. Pot the cutting in damp soil and water regularly until new foliage emerges. While the cutting can also be started in water, such cuttings generally don’t survive when transplanted in soil.
Propagation by division
Individual plants can be divided every 3 – 4 years in spring, as soon as new foliar growth emerges, dig a spade into the soil and lift out the entire clump. Split apart the root clump into several new sections and replant the divisions straightaway. Water them well.
If you’re using good or average soil to grow these plants, you most likely won’t need to feed the plants. However, if you think that the soil is lacking in nutrients, a general-purpose, slow-release fertilizer applied once in early summer will provide sufficient nutrients for the plants.
One disadvantage with feeding these plants is that they might start spreading. These plants typically don’t require fertile soil to thrive well. Sandy or somewhat infertile soil will work just fine for these plants and might even make them flower more and grow bushier than they would in rich soil.
These plants are not typically fussy and don’t need much pruning during their growing season, apart from deadheading spent flowers or if they spread too much. Old flower stems might have to be pruned down when the flowering season ends. However, it’s easier to prune them down once their growing season ends in early winter when frost kills off the foliage. Plants that get too tall might have to be staked as the stems will flop down, particularly in windy conditions.
They are generally resistant to diseases but can be subjected to aphid invasion on occasion. Use insecticidal soap if this happens.
Over-watering is a concern since these drought-tolerant plants can easily develop root rot. Well-draining soil is a must as well as judicious watering.