Caren White is a Master Gardener and instructor at Home Gardeners School. She has been associated with Rutgers Gardens for over a decade.
Love bittersweet but hate how it takes over your yard? Try growing American bittersweet, a native plant that is easier to control while providing berries that add color to the winter landscape.
What is American Bittersweet?
American bittersweet is a woody perennial vine that is native to North America. It is hardy in zones 3 through 8. The vines are commonly found in the woods growing on trees. They can attain a length of 20 to 30 feet. The vines are dioecious, meaning they are either male or female. You need both to produce the berries. The male flowers are very inconspicuous. The female flowers are larger but still small. Both are green. Bloomtime is late May through June. The vines need pollen from the male flowers to fertilize the female flowers. Only the female vines have berries which appear any time from June through November. The berries start out orange, but that is just a capsule covering the actual berries. The capsules open in the fall revealing the red berries.
The berries are an important food source for birds and animals in the winter. Songbirds, pheasants, Ruffed grouse and even foxes eat the berries. Unfortunately, the berries are toxic for humans causing vomiting and diarrhea.
What is the Difference Between American Bittersweet and Oriental Bittersweet?
American Bittersweet is a native plant that is relatively well-behaved. Oriental Bittersweet is an exotic that has become a dangerous invasive plant. The term “exotic” refers to the fact that a plant is not a native plant. It has been imported from another part of the world. Many imported plants become what’s known as “invasive plants” which means that they grow very quickly and crowd out the native plants.
Oriental bittersweet is native to China, Japan and Korea. It was introduced into the United States in 1879 as an ornamental plant. It has escaped from gardens and naturalized in the landscape. It is much larger and faster growing than American bittersweet, growing as much as 60 feet in one year. It not only climbs trees, it kills them. The weight of the huge vines topples even the largest trees. The vines are very thick, often reaching 4 inches in diameter. They don’t just climb trees, they twine around the tree trunks and squeeze them in a process known as “girdling”. Eventually they strangle the trees and kill them.
How to Grow American Bittersweet
If you want to grow American bittersweet for its colorful berries, you will need both a male and female vine. Without a male vine to pollinate the female vine, you will not get any berries. Plant your vines in a sunny location with good drainage. American bittersweet will tolerate some shade, but grows best and produces the most berries in full sun.
The vines grow 20 feet high and 20 feet wide so they will need support. Despite the fact that they climb trees in the woodlands, it’s not a good idea to encourage your vines to climb trees or shrubs in your yard. Large mature trees can bear the weight of the vines whereas the smaller trees and shrubs commonly found in our yards will be smothered. Provide your vines with a sturdy trellis or fence to grow on. If you are growing your vines on a trellis by a building or wall, be sure to place your trellis several inches away from the wall to allow for air circulation between the vine and the wall. American bittersweet is prone to powdery mildew which occurs when there is poor air circulation.
Water the vines when there is less than one inch of rainfall per week. You will only need to fertilize once a year in the spring. Apply a shovelful of compost or slow release fertilizer at the base and work it into the soil.
How to Prune American Bittersweet
Pruning should be done in the winter when the vines are dormant. Remove any damaged or diseased branches. You will also want to remove any branches that produced berries. This will encourage new growth in the spring. American bittersweet blooms on “new wood” which is the new growth that appears in the spring. Branches that have already produced berries are considered “old wood” and won’t bloom and produce berries again which is why it's a good idea to prune them away to encourage new growth that will bloom and produce berries.
Sometimes, no matter how diligent you are about your pruning, the vines will grow and become a tangled mess. This is not a problem. Just prune the entire vine down to ground level. Don’t worry, it will grow back in the spring with the added advantage that all of the branches will be “new wood” and will all flower and produce berries.
How to Grow American Bitterweet From Cuttings
When propagating American bittersweet vines by cuttings, remember that each vine is either male or female. Cuttings from a female vine will result in female vines and cuttings from male vines will result in more male vines. You need both a male and female vine to produce berries. So if you want berries, be sure that your cuttings aren’t just from a male vine. Male vines do not produce berries.
Softwood cuttings refer to cuttings from woody plants that are taken from the ends of the branches in spring or early summer while they are actively growing and not yet hard and woody. The advantage of taking softwood cuttings is that the branch is growing and once separated from the plant, will quickly grow roots.
Take a cutting that is 3 to 5 inches long from the end of a branch in midsummer. Strip the foliage from the bottom half of your cutting. Dip it in rooting hormone to speed up the growth of roots. Then gently plant it in a container with soil that is 2 parts perlite and 1 part sphagnum moss. Place the container in a sunny location, keeping the soil moist. Roots should appear in 2 to 5 weeks. You will know that your cutting has roots because new leaves will start growing. Plants without roots cannot grow new leaves.
Hardwood cuttings are taken during the winter when a woody plant is dormant. The advantage of propagation by hardwood cuttings is that your cutting will have rooted and started growing by the spring so that you can plant your new vine after all danger of frost has passed.
Take a cutting that is 6 to 10 inches long from the end of a branch. It’s okay that the branch has no leaves. Dip it in rooting hormone to speed up the growth of roots. Gently plant it in a container with a mixture of 1 part sphagnum moss and 2 parts perlite. Water the soil thoroughly and then cover both the plant and the container with a clear plastic bag. Place the container with your cutting on the north side of your house where it will not get direct sunlight which could fry your plant. There is no need to water your cutting. The plastic bag will act as a greenhouse keeping your cutting warm and moist. In the spring, your formerly bare cutting will start growing leaves. That tells you that it is time to remove the bag. After a week of getting acclimated to the outside, your cutting will be ready to plant.
How to Grow American Bittersweet From Seeds
American bittersweet is very easy to grow from seed. Harvest the berries in the fall after the capsule has opened. You don’t need the capsules, just the berries. Spread the berries on a paper plate or paper towel in a single layer and allow them to dry for 2 to 3 weeks. When the berries are dried, remove the seeds from them and dry just the seeds for an additional week.
The seeds need to be cold stratified to germinate. Cold stratification mimics winter weather which is what the seeds experience in nature. They have evolved to only germinate after the cold weather has passed and the warm spring weather has commenced.
Sow the seeds in a container, lightly covering them with soil. Moisten the soil. Then cover the container with a clear plastic bag and place it in your refrigerator for 3 months. After 3 months, the seeds should start to germinate. That means that it is time to remove the container from your refrigerator and remove the bag. Place the container in a sunny place indoors. Your seedlings will be ready to transplant outdoors after all danger of frost has passed.
Questions & Answers
Question: Can I overwinter my Bittersweet in it’s clay pot in Zone 5?
Answer: Clay pots frequently crack or break during colder weather. This is because the clay is very porous and absorbs water. When the temperatures fall below freezing, the water freezes and expands, cracking or breaking the pot. It is also very difficult to overwinter anything in a container because the entire rootball is exposed to the cold winter temperatures and may freeze. The reason that perennial plants survive winter weather is because their roots are in the soil below the level where the soil freezes. They are insulated from the freezing weather. If you dig a hole in the winter and get below where the soil is frozen you will discover that the soil underneath the frozen layer is warm. I've actually done this! This warm layer is where the roots of perennial plants live. In areas where the soil freezes deeply enough, the roots will die which is why so few plants are hardy in the coldest growing zones. Only plants with very deep roots that can get below the deep-frozen layer of soil can survive.
Question: So if I only have berries from the that I saved American Bittersweet plant, then I only have female plants correct? I can start to germinate them in the fridge but nothing will happen because I need a male plant.
Answer: The female vines produce both male and female seeds just as female humans produce both male and female babies. There is no way to tell the male and female seeds apart. You have to wait until after you have germinated them and the vines have grown enough to start flowering to know which are the male vines and which are the female vines.
© 2018 Caren White
Caren White (author) on August 30, 2020:
I don't recommend growing bittersweet in a container because the soil in the container will freeze during the winter and kill the roots of your plant. Perennial plants survive the cold winter weather because their roots are growing below the frost line where the soil never freezes.
Scarlet Maggi on August 29, 2020:
Thanks for your info. I have it in my mind to split the root of my existing American Bittersweet. I planted it in the front of my bay window in the front of my house, because most things do well there. It has done really well over the last three years and is climbing up the front of the window and the house. I know I can prune it back, but I would like to leave part of the root in the front which I can control and plant half of the root in a large deep planter and let it grow along the long fence.
What are my chances of success? Also when would be the best time to do this. I live in Toronto, Ontario Canada, where winter can be severe, but not lately. Thanks.
Caren White (author) on May 09, 2020:
It sounds like you either have a male vine (male vines do not produce berries) or you have a female vine with no male vine to pollinate it . Without pollination, the female vines will not produce berries. Take a look at the flowers when your vine blooms. If you can barely see them, it is a male vine so you need to buy a female vine if you want berries. If the flowers are larger, then you have a female vine and you need to buy a male vine to pollinate it.
John Young on May 08, 2020:
Our bittersweet does not yield berries what should we do?