American bittersweet (Celastrus scandens) is one of the most ornamental of our hardy northern vines. This deciduous, climbing woody vine is native to our area and is found growing in thickets, in stands of young trees, along fence rows and streams. It grows vigorously and can kill shrubs or small trees to which it becomes attached merely by tightly girdling stems and branches.
Chinese bittersweet (Celastrus rosthornianus) is sometimes sold in Minnesota. It suffers winter injury most years in the northern half of the state, often dying back to the ground. It is normally hardy in the southern half, but can suffer injury some years. Bittersweet makes no appreciable floral display, however the fruit can be exceptionally beautiful. The clusters of yellowish-orange capsules separate, exposing bright, red-orange berries about September. These remain attractive through most of the winter. Cut and brought indoors, they make excellent long-lasting decorations. The leaves, bark, and fruit are considered toxic, however, and should be kept out of the reach of young children and pets.
Bittersweet vines grow well in most soils, in full sun or shade, though adequate sun is important for fruit production. The only attention they generally need is a little pruning to keep the plants tidy or to limit their size. This may be done in late winter or early spring.
Bittersweet is a dioecious vine having male flowers on one plant and female on another; the two types must be near each other to produce fruit. In May or June, small greenish-white flowers open in clusters at the ends of branches. Bees are the main pollinators, although wind may also be involved.
Plants can be bought from a nursery in spring or propagated from seeds or cuttings. To start them from seeds, collect the ripe fruit as soon as the capsules have split to reveal the crimson berries, sometime between mid-September and November. Spread the collected fruits in shallow layers and allow them to dry at room temperature for 2 or 3 weeks. Then remove seeds from the capsules and allow them to dry for another week.
It's easy to raise new plants from seeds sown outdoors in fall or spring. Seeds sown in the spring must first be placed in moist sand or peat in a bag or container and kept in the refrigerator (34° to 41°F) for 3 months. This breaks dormancy and promotes seed germination.
Seedlings will average about 50% each, males and females, but you can't tell which till they're old enough to bloom. You only need one male to serve as a pollinator for every six or eight females. The females will all bear the attractive fruit. The best way to get the sex ratio you want is through vegetative propagation of plants from cuttings of known sex.
Softwood cuttings can be taken from terminal (tip) shoots that are soft and immature with two or more nodes (the point on the stem where a leaf is attached). The 3-5 inch cuttings, with leaves attached should be taken in midsummer, cutting squarely across the stem just beneath a node. Remove the leaves on the lower half of the cutting and dip the base of the cutting into rooting powder. Rooting powder can be purchased at a nursery under a variety of names, for example: Hormex, Hormodin, Hormo-Root, Rootone, etc. The best method of application is to spread a little of the powder on a sheet of plastic or wax paper, dip the base of each cutting in this, then shake off any surplus and plant the cutting immediately. The cuttings can be rooted in potting mix of 2 parts coarse perlite to 1 part sphagnum peat.
The double-pan technique is an easy and successful way of rooting cuttings. Use two flower pots, at least 4 inches deep with one so much larger than the other that when the smaller pot is set inside the larger one, there is a 2-inch space between their rims on all sides. The inner pot should be clay, the other pot plastic. Plug the hole in the bottom of the smaller pot with a cork and set the pot inside the bigger one so their upper rims are level. Fill the space between the two pots with potting mix and insert the cuttings. Water with a fine spray and fill the inner pot with water.
Cover the cuttings and pots with a clear plastic bag and place them in bright, but indirect light. No further overhead watering is necessary. Sufficient water should pass through the porous sides of the small pot to maintain the potting mix in a moist condition. Keep the small pot full of water. If moisture collects on the inside of the plastic bag, open it to provide a bit of ventilation. The cuttings will produce roots in 2 to 5 weeks. Plant them outdoors in a protected location, as soon as they're rooted.
Hardwood cuttings, on the other hand, should be taken during winter when the plants have no foliage. Include at least two nodes in the 6 to 10-inch cuttings. Make the cuts squarely across the stem just below a node, then make a slant cut ½ to 1 inch above a node. The difference in cuts will aid in distinguishing between the top and base of the cuttings when planting them. Dip the basal or square cut end in rooting powder and plant them in a plastic flower pot filled with the perlite and peat potting mix. Water the mix, then enclose the pot in a sealed clear plastic bag. Place the pot outdoors on the north side next to the house and check periodically to see that the pot hasn't tipped over or dried out. Frozen condensation inside the sealed plastic bag is an indication that moisture is present. Add a handful of snow to the pot and reseal if the bag is dry. The cuttings will be rooted by May and producing leaves. Remove the plastic bag but leave the pot in the shade for another week before transplanting the rooted cuttings to a selected site.