SMALL-FLOWERED GROUP (continued)
The Heracleifolia Group contains plants that have at least one parent that belongs to the Subgenus Tubulosa which includes C. heracleifolia, C. stans and C. tubulosa. Plants in this group are mostly shrubby, but sometimes climbing in nature. Interestingly, the bell-shaped or flattened flowers are either hermaphrodite or unisexual with male and female flowers on the same or separate plants.
A cross between C. heracleifolia and C. virginiana produced the well-known C. ‘Mrs. Robert Brydon’. This semi-climber is often used to spill down slopes or over walls where its clusters of small, open, white flowers that are edged with blue continue throughout the summer into the fall. Another cross with a similar usage and equally long bloom period is C. ‘Praecox’.
This group also contains selections from C. heracleifolia that are more upright and shrubby. C. heracleifolia ‘Cassandra’ forms an open shrub with large leaves and tubular, fragrant, gentian-blue flowers throughout the summer. We also grow a dwarf form of C. heracleifolia which was found on Omeishan in China. This forms a foot tall, small-leaved shrub.
All plants in this group are herbaceous and should be cut back during the winter to promote new growth in the spring. Because the plants in this group have fine roots, bury them the depth that you find them in their pots. Do not plant them deep.
Plants in this group are generally non-climbing or only semi-climbing. Most are derived from the species C. integrifolia which is an herbaceous perennial with stems generally growing from one to three feet. This tough species is found from Central Europe across Russia and into West and Central Asia. The stems of C. integrifolia have single nodding bell-shaped flowers at the terminals and sometimes at the ends of axillary stems. The many selections from the species produce numerous stems and are quite attractive in the mixed border. Some selections from the species, such as the white-flowered C. ‘Hakurei’, have a sweet fragrance that is sometimes described as citrus-like.
In addition to selections from this species, the Integrifolia Group also includes crosses between C. integrifolia and C. viticella (and others). (Plants from these crosses are often placed in the Diversifolia Group but that is not a group that is recognized yet by the Royal Horticulture Society and therefore we still include them here.) These plants are woody although they bloom on the current year’s growth. We cut these plants back hard during the winter. The flowers of these crosses are generally much larger than those of the species and they tend to be variable. C. x durandii has rather large flattened indigo flowers. C. ‘Alionushka’ has large rose-colored bell flowers. Both produce long stems that can be tied up on a trellis, conducted through a neighboring shrub or be allowed to ramble through the garden where their flowers will bloom with surprising companions.
We grow plants in this group in full sun and with good drainage. If they are lightly dead-headed from time to time, it is not uncommon to have them in bloom for three months or more. We have found C. x durandii to be one of the most drought-tolerant clematis in our gardens.
Clematis in this group are among the easiest and most rewarding for gardeners but they are still underused. Because of their heritage, they are extremely cold-hardy. That fact alone should make them welcome in regions with harsh winters. Many also hold up well to heat. In especially cold climates, plant the roots deeper to protect them from heaving and thawing in the winter.
One exception to the “non-climbing” rule in this group is C. ‘Rooguchi’ which is a cross between C. integrifolia and C. reticulata. It does climb (if laxly) and its stems are not woody. We include it here because of its ancestry. This vine has countless fleshy plum-colored bells. We have had reports from customers in warm Southern states who have success with this vine. We have also had reports of it growing successfully in Michigan. When the plant is young, it can exhibit powdery-mildew. We cut it back hard if we see this. It will soon grow new clean stems and bloom a little later in the season.
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