Questions on: Clematis

Ron Smith, Horticulturist, NDSU Extension Service

Q: I have autumn clematis that grows beautifully all summer. However, this year the buds set, but then dried up on the still growing vine. Last year I replaced the old and falling apart trellis. The plant does not seem to be wrapping around the trellis very well. Could this be the problem? I am mystified and obsessed by this problem. Can you help me? Thanks. (e-mail reference)

A: You might be thanking me too soon because I'm not sure what the problem is with your clematis. The plant needs alkaline soil and cool roots, which usually is accomplished with a little mulch. I don't think the trellis has anything to do with the problem.

Q: I read an article on pruning clematis, but I’m not sure the advice is appropriate for the Fargo area. The author wrote that no matter where you live, it is best to let your clematis stay unpruned and dormant until spring. If you have a plant such as a jackmanii, you should then cut the entire plant down near the ground. Do I need to prune above a pair of leaves? I would appreciate any advice you can give me. (Fargo, N.D.)

A: The advice you read is probably something that the author has done every year with good success. However, there is plenty of clematis that never gets pruned until this time of year, but still does OK. The Jackmanii group blooms on new wood, hence the advice to cut the plant down to ground level, which assumes the owner wants blooms to that extent. Otherwise, cut them where you wish. They will bloom on the new wood produced.

Q: I have a gorgeous clematis growing on my trellis. It grows huge purple flowers that bloom late in the spring, but in July, the blooms die and the vines and leaves turn brown. Should I be pruning? Is this growing pattern normal? In the winter, should I prune the plant off the trellis? I was told not to do that by a relative, but it is ugly. (e-mail reference)

A: It is best to prune in the early spring. As to the decline in the visible quality of the plant, you might try moving it next spring, before new growth takes place, to an eastern exposure so the hot sun won’t cook the plant as much.

Q: I have six-year-old sweet autumn clematis that is diseased for the first time. The leaves turn tan/brown, then die. New growth still is occurring and flower buds are appearing. The diseased leaves have “spiderlike webs” going through them, but I cannot see any sign of insects. (e-mail reference)

A: It sounds like spider mites. Place a piece of paper under some of the leaves that are affected and shake the branch or leaves a little. If the specks that land on the paper move, you have spider mites. If that is the case, get a miticide and give the plant a good spraying. Also, a hard spray with plain water may bring them under control.

Q: I would like some information on clematis. What varieties are hardy to southeast North Dakota? Could you also please tell me the colors of these varieties and give me hints on growing them? (e-mail reference)

A: Clematis (Clematis hybrids) is probably the showiest of the vines that can be grown in the Upper Midwest. It grows best where it doesn’t get too hot. It does well with an exposure to the east, but if it is grown on the south and west side of a structure, the clematis will benefit from midday shade. Clematis does best in a cool, moist soil, but the soil must have good drainage. The soil can be kept cool during the growing season by using organic mulch, such as sphagnum peat moss, which also will help keep the soil more acidic. Clematis climbs by leaf petioles that act like tendrils. Most clematis will bloom on the current season’s growth, if cut to the ground in the spring before growth starts. Some clematis is useful as ground cover. I would encourage you to visit local garden centers, but not the national chains, to see what they have for sale. Small- business owners will not sell anything that is not hardy to the area and you can then choose the plants you want. I do not suggest making mail-order catalog purchases of this vine.

Q: I live in zone 4. I recently purchased dormant clematis roots and am storing them in a cool place. When should I plant them? My thinking is that perennials go dormant and live in the cold ground all winter, so I should be able to plant the roots right now. Is this true or do I have some crazy idea? You always have given me such good answers to my questions. (e-mail reference)

A: Clematis can be planted as soon as the frost is out of the ground. Glad my past answers have been helpful. Thank you!

Q: I have read conflicting advice on how to prune clematis. I have a red trumpet vine, alpina clematis and Montana clematis. The tags seem to say two different things in regard to pruning. Do I prune after flowering in the summer or in the dead of winter? (E-mail reference)

A: Simply follow the tag directions. Some clematis should be pruned now, in early spring, while others that bloom in late spring can be pruned back right after flowering. If it is from the Jackman group, which is the largest and most popular group in America, then pruning can take place this spring as the buds begin to swell. My advice on following what is said on the individual tags comes from the fact that I have no specific information on the names of the clematis you provided.

Q: For the past two growing seasons my clematis has grown normally in the spring until it is about four feet tall. Then the lower leaves start to become mottled yellow. By July, the lower half of the vines have mottled leaves which then start to yellow completely, bleach out and finally turn brown. The plant is about five years old. It is growing on the south side of our shed and each spring is top dressed with composted sheep manure. Do you have any insight into what is causing these symptoms and how I can avoid them next year? (Bismarck, N.D.)

A: I really don't think your clematis has a disease problem. Your plant is having a physiological reaction to late summer stresses. Simply clean up the leaf litter and your plant should be okay next year.

Q: I have some clematis vines on a trellis in my yard and wonder if I should cut them back or just let them be. I have read publications that recommend cutting back the vine and covering with mulch. Other publications recommend leaving the vine alone and covering the base with mulch. (Jamestown, N.D.)

A: I guess either way would work but it has been my practice and recommendation to prune back in the spring to encourage new growth. That way you can see what has or has not survived the winter. Be sure to mulch the base generously just prior to freeze up.

Q: I’m looking for information on the fall care of clematis. We recently moved to this location and discovered the clematis. How do I prepare it for the winter months? (Mobridge, S.D.)

A: When you say "discovered" clematis, I assume you mean that you purchased the property and found out you had one growing there. Clematis only needs a basic mulch cover on the crown after the soil freezes. Keep it moist before freeze up and it should get through the winter in good form.

Q: I have a rather large garden where the soil has turned to cement. The plan is to add some city compost to it and rototill it in. The clematis in our garden have been there for well over 10 years. How far away from the clematis do we need to stay so that the roots are not damaged? I would also like to take two sections from the clematis but after looking at it closely, I only see four stems coming out of the ground. I'm afraid that I will damage the plant. Should I just buy some different ones to plant? (Moorhead, Minn.)

A: That last idea of yours sounds like a good one. You don't want to mess with something that is as happy as your clematis appears to be. It should suffice if you stay a good 24 30 inches away from the plant. A word of caution about the compost, get it tested first. I found the compost from Fargo to be very high in salts when I tested it years ago. If diluted with sufficient soil, it isn't a problem. Salt toxicities begin to occur with sensitive plants if the compost volume is higher than 20 percent in the root zone. Since the compost material is collected from all over, there may be some herbicide residue that has not broken down into harmless metabolites. If it is really important to you to improve your soil, I encourage you to get some sphagnum peat moss this fall, and work it into the soil.

Q: When is the best time to transplant clematis? (Ontario, Canada)

A: In the early spring when it’s dormant or this fall after leaf drop.

Q: An individual told me that their clematis plant along the deck has damage to the leaves. The leaves are curly and black around the edges. The plant is still blooming. I was wondering if heat is causing the problem because the plant is near a heater vent, and they do not withstand heat to well, correct? We have been dry in this area, so I find it hard to believe it is a fungus. (Steele, N.D.)

A: Clematis like early morning sunlight (east exposures) best. They also like to have their root systems kept moist and cool, which is accomplished with generous organic matter mulching.

You are likely correct; the plant might be responding to excessive temperatures.

Q: My clematis is 4 years old with large purple flowers. This year I found one of the flowers was variegated with purple and green... very beautiful. I would love to know if I propagate this stem, would it come out this variegated color, or the purple? What would have caused this to happen. I would not be disappointed if all the flowers turned like this. (E-mail reference)

A: This is likely a somatic mutation called a chimera. Many new crops or varieties have been introduced this way. I would encourage you to propagate it vegetatively - via a cutting - and see if it is carried through on the new propagule. If so, then you have discovered a new variety to introduce to the rest of the world. A local nursery may be interested in purchasing it from you for royalty payments or an outright payment.

Q: At what time of the year does one trim global arborvitae? Should Potentilla be cut back and when? Does one cut back Clematis in the fall, spring or not at all? (Grenville, S.D.)

A: The best time to trim your arborvitae is in the spring when active growth can take place. Cut the potentilla back in early spring prior to leaf-out. Most clematis varieties bloom on new growth produced in the spring. Cut back in early spring to about 6 inches of old growth remaining.

Q: I read in a magazine that there are three easy ways to start new plants from a clematis, but I lost the article. Could you please tell me how to start new ones from my original plant? Also, what is the best way to prepare it for winter? Should I cut it back or leave the vines on the trellis? (Tower City, N.D.)

A: Clematis can be propagated by softwood cuttings taken in the spring under mist in about five to six weeks. Semi-hardwood cuttings taken in late spring to late summer (now!) work better. You likely have the jackman clematis, which blooms on new growth each spring. The usual suggestion is to cut it back to about 12 inches above the soil line at that time. Many folks will do that operation in the fall before the snow flies, then mulch heavily. Either way seems to work out.

Q. I have a vine from the clematis family. It has little white flowers that are very fragrant. Every year at this time a white mold (fungus?) appears at the base of the plant and creeps up the whole area, shuts off the blooming, and leaves die. Any suggestions on how to prevent this problem? (Cresbard, S.D.)

A. It sounds like a bad attack of powdery or downy mildew, which is a fungus. To control, use a copper-based spray like bordeaux mixture. My bet is it is downy mildew, as this is the more destructive of the two fungi.

Be sure to destroy all affected foliage this fall. Avoid overhead watering and get the spray down before the symptoms appear.

Q. Can you tell me why my clematis leaves are turning yellow? Also, how do I get my Christmas cactus to bloom? (Wimbledon, N.D.)

A. Classical symptoms of manganese (Mn) deficiency! Could be brought on by poor drainage or low organic matter content in the soil. Another possibility could be excess iron being available from a chelated form being applied.

When the interveinal chlorosis shows up on older foliage like this, and the new growth appears normal, it is manganese deficiency. Iron deficiency shows the same symptoms, but on the new growth only.

What to do? There are several manganese formulations available. I would suggest looking for a Mn EDTA chelate or an organic complex. This is a trace or micro-element, so not much is needed. If you have not mulched the clematis with peat moss or compost, I'd suggest doing so.

Q. Three questions: One, how can you divide or increase clematis vines? Two, I have 40 to 50 crocus bulbs that are 3 years old. They grow beautifully, but only four or five blossom. Why, and what can I do to make them blossom? And three, I have an ornamental almond bush that has blossomed for three years and is spreading. Can I cut back some of the stems to control its size without harming it? (Robinson, N.D.)

A. 1. Clematis can be propagated just about any way you want—by seed, cuttings or root division. The easiest way is by stem cuttings on spring wood or later in the spring after the wood has matured. Leaf-bud cuttings taken in summer that can be kept under mist also root easily.

2. You may have them planted too deep, or they may need fertilization.

3. Yes, you can prune the almond to a more desirable shape with no harm done.

Q. Can you tell me the best way to put a clematis to bed? Should I cut them back now? I also have a large ash tree that provides good shade, but the interior branches are dead and leafless. The outer branches look fine, and I cut back the deadwood. Can you tell me what we should do with it? (Moorhead, Minn., e-mail)

A. The Jackman group of clematis, which blooms vigorously on new growth each season, should be pruned back each spring to within 6 inches of last year's wood. It may or may not send up some new shoots from the crown. If these should appear, cut back all old wood to ground level. As the season wears on, pinch back the new growth with your fingernails to encourage branching and a fuller vine.

Some internal branch die-back is normal on all deciduous woody trees. If it continues or becomes extensive, and all the leaves or branches show some necrotic or cankered areas, then some corrective action should be taken. If the tree is really important for your property, I would have a professional arborist come out and give you a diagnosis, along with providing some corrective action to take.

Q. What do you do with clematis growing on a trellis after a hard frost? Do you cut it back to the roots or leave it alone? The black leaves and stem look unsightly. Thank you. (Orient, S.D.)

A. You can prune clematis now as it produces blooms on new growth that will emerge next spring.

Q: Is it possible to propagate clematis successfully by root division? If so, what is the best way of doing so? (Biggar, Saskatchewan, Canada, e-mail)

A: Propagation of clematis can take place a number of ways: seed, cuttings, grafting, root division or layering. Of all those choices, the easiest way to propagate them is via cuttings taken from young wood in the spring, but semi-mature wood taken in late spring also works and is more commonly used commercially. Perhaps the easiest way to propagate this species is by layering. Simply bend one of the stems over and pin it into the soil, allowing the tip to remain upright and in the daylight. It should root in about four to six weeks.

Q: Could you tell me how to start new plants from my clematis? (Williston, N.D.)

A: Clematis can be summer propagated by cuttings in a 50-50 sand/peat mix. Seed can also be collected and planted after 60 to 90 days of stratification at 40 F, or it can be collected in late fall and directly planted in a greenhouse or sunny window for germination about three and a half months later.

Q: Several years ago I purchased a Clematis plant at Walmart. It grows and grows, but does not bloom. Is it possible to get a Clematis that is not for our area? (Grand Forks, N.D.)

A: There are as many Clematis as Smiths! So, yes, it is possible to get a non-adapted Clematis - especially from national chains where purchasing decisions are made in one location for the entire country. I’d suggest looking for a Jackman variety of Clematis. They seem to do best in our area and are looking especially good this year!

Back to Flowers Menu
Back to the Hortiscope Table of Contents