Answer: Clematis are relatively hardy plants and generally easy to grow, so don't give up on yours yet. If their needs can be met by the site and proper care, they will thrive. Clematis require full sun to grow best (6+ hours direct sun per day) though some dappled shade during the heat of the day is beneficial. Flowers of some red and blue large-flowered hybrids and the bicolors fade badly if they get too much sun (such as 'Nelly Moser,' 'Hagley Hybrid' and 'Hybrida Sieboldiana') and these should be planted in eastern exposures or partial shade. The site should be open enough to allow for air movement around the plants. Soil should be rich and well-draining with a pH close to neutral (7.0). Though the plant's stems and foliage should be in sun, the roots like a cool, moist environment. With the exception of C. montana, clematis do not compete well with large tree roots. Most clematis will require staking so the twining leaf petioles can cling and climb upward, though some gardeners choose to let the plants sprawl over the ground, over woodpiles, other plants, etc.
Begin with a soil test to determine if the soil pH or the phosphorus level needs correction. If so, make corrections before planting. Soil in the planting area should be prepared to a depth of 24 inches in an area approximately three feet wide. It is best to incorporate one-third by volume some compost or rotted manure to help improve aeration and drainage.
After amending the native soil for planting, dig a hole to accomodate the root system. Cut stems back to 12 inches in height. This will help the plant branch as it begins to grow and will reduce the chance of stem breakage during the planting process. Clematis are planted with the crown one to two inches below the soil surface (this enables the plant to recover should it be mowed off, damaged by animals or infected with clematis wilt). Once the plant is in the hole at the proper depth, fill in with the backfill soil, firm and water well to settle soil around the root system. If planting bare root plants, soak the roots in a bucket of water for an hour before planting to fully hydrate them. After planting, place a protective collar of hardware cloth or chicken wire around the base of the plant to protect against damage from mowers, string trimmers and animals. Because clematis prefer a cool root environment, plan to underplant with a groundcover or perennials that have shallow, non-invasive roots. Artemisia 'Silver Mound,' hardy geraniums, creeping phlox, coralbells, candytuft and most veronicas work well. A two-inch layer of mulch, low shrubs, or paving also provides a cooler root environment. Clematis may seem a bit slow to establish. In the first season, there may be little growth and few or no blooms. However, it is important to get the roots well established. Fertilize annually for rapid growth during establishment with a 3:1:2 or 4:1:2 ratio fertilizer. Apply one-half pound of a 15-5-5 fertilizer to the soil in the 50 square feet surrounding each plant. Fertilization may not be needed or desired once the plant is established and growing well. Plants will need about one inch of water per week during the growing season applied through irrigation or rainfall for good establishment.
Once the plant is well established, some basic care is needed on an annual basis. In dry seasons, watering deeply once a week is recommended. Renew mulch to a two-inch depth in late spring after the soil has warmed unless a groundcover or other method is used to cool the root environment.
The main purpose in pruning is to help plants produce the maximum number of flowers. Annual pruning is recommended. Sometimes older, neglected plants can be cut back into older wood and new buds may break. Growth from old wood will likely be weak and slow, however. If no pruning were done at all, plants would still grow and flower profusely, though not where you may want them to. Some flowering would occur high in the plant and out of sight. Not all clematis can be pruned in the same way. There are three methods that can be applied to major groups depending on the time of year the plant flowers. No new growth must occur to enable the earliest flowering clematis to bloom, but the later flowering types must make new growth in order for flower buds to form. A few plants are not strictly bound to the following groups but may cross lines. Because vines will likely be entangled, make cuts carefully among the intertwining vines and spread and train them in various directions in order to cover the maximum possible area. This enables the plant to display its blooms rather than be bunched up.
Hope this information helps you correct the growing environment for your clematis so they will thrive.
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