Regular feeding and watering will reward you with a large vine blanketed with white flowers by early fall. After flowering is complete, the vine should be rigorously pruned to limit the self-seeding that can lead to the invasive spread of the plant.
Light
Plant sweet autumn clematis in full sun for best flowering. However, these vines can tolerate a considerable amount of shade—unlike most other clematis species—if you are willing to put up with some reduced flowering.
Soil
The plant is not fussy about soil conditions if there is good drainage. The ideal soil will have a slightly acidic to neutral soil pH, but even slightly alkaline soils generally support the plant quite well.
Water
Sweet autumn clematis has average water needs. Roughly one inch of water per week, through rainfall or irrigation, is generally sufficient. Withhold additional water during rainy spells, as this plant doesn’t like to sit in wet soil.
Temperature and Humidity
Sweet autumn clematis grows vigorously in the climate conditions across its entire hardiness range from USDA growing zones 4 to 9. It does not have particular humidity requirements.
Fertilizer
Like all clematis species, this plant is a heavy feeder. Apply a low-nitrogen fertilizer, such as 5-10-10, in the spring. Then, repeat feeding every few weeks throughout the growing season.
Pruning
This vine blooms on new wood, so prune sweet autumn clematis after flowering finishes in the late fall. Doing so will remove the seed heads and prevent self-sowing. Some gardeners cut their sweet autumn clematis plants down to within one foot from the ground. But if you want the vine to cover a large area, such as a large pergola, you can prune less severely and leave more of the plant in place.
Propagating Sweet Autumn Clematis
It is rather rare that a gardener would need to propagate sweet autumn clematis. But if you want to share plants, the seedlings that sprout up around a mature plant can be transplanted wherever you wish. Stem cuttings can also be easily rooted. Simply cut a four- to six-inch stem segment, plant it in ordinary potting soil, and keep the soil moist until roots develop. This can take six to eight weeks.
How to Grow Sweet Autumn Clematis From Seed
Seeds are best started in the late fall to early winter. Use ordinary potting soil in small seed-starting containers. Place them in a sunny window; sweet autumn clematis will germinate and grow quickly. Seedlings can be moved outside once nighttime temperatures remain above freezing.
Potting and Repotting Sweet Autumn Clematis
Sweet autumn clematis grows well in containers. Choose a large pot, 15 to 18 inches in diameter. Keep in mind that clematis will want to climb, so installing a trellis or arbor in or near the pot is highly recommended. Use potting soil that has been blended with a general-purpose, slow-release fertilizer, paying close attention to the instructions on the product label. When repotting, increase pot size a few inches larger than the last.
Overwintering
Sweet autumn clematis is quite hardy, to a point of no worries for the home gardener for overwintering; it will bounce back strongly in the spring as soon as the temperatures rise. Even plants grown in containers will do fine, as long as the container will not freeze; for instance, avoid ceramic or terracotta potters.
Common Pests and Plant Diseases
As with other clematis species, sweet autumn clematis is prone to clematis wilt, a potentially fatal fungal disease. Foliage might appear dry, withered, and even black on affected plants. Prune out and destroy affected foliage. As long as the disease hasn’t spread throughout the entire plant, it will usually bounce back the next growing season. Powdery mildew, leaf spots, rust, and viruses can also affect the plant, though generally, they are not fatal. Insect pests include aphids, slugs, snails, scale, earwigs, and spider mites. With these issues, look out for discolored foliage, small bugs on the foliage, and the plant generally failing to thrive. Use the appropriate fungicide or insecticide for the problem.
How to Get Sweet Autumn Clematis to Bloom
Sweet autumn clematis is a very hearty grower and can bloom in even lackluster soil, given that it receives a solid six to eight hours of sunlight each day. The plant produces deep roots, so when you are transplanting a plant to a different place in the garden, ensure the roots sit at least three to four inches underground to keep the roots cool and the plant thriving during the heat of the summer. The blooms usually begin in August and continue through October. Ensure the plant has a trellis or other structure to climb. For the best profusion of flowers, prune clematis back to about one foot above the ground after one season of growth. In the coming years, prune the plant down to two to three feet above the ground after the flowers have died back.
Common Problems with Sweet Autumn Clematis
Though clematis is an easy plant to grow and quite hardy even in the presence of insects or disease, it can be easy to remedy any problems that do pop up.
Spots on Leaves or Wilting Plants
Dark spots on the leaves could be thanks to clematis wilt, leaf spot, or root rot, all of which can be caused by overwatering and poor air circulation. Thin the plants to allow better circulation and remove any infected leaves. Serious problems could benefit from a fungicide. Note that yellow mottling or spotting on the leaves is often a sign of tomato ringspot virus, which can reach your sweet autumn clematis through the travel of nematodes. This diseases requires removing the affected plants.
White Fungal Growth
The white fungal growth on clematis leaves is often powdery mildew, a common problem that can make leaves wither and die. To treat, remove heavily affected leaves and apply copper sulfate, sulfur, or potassium bicarbonate.
