In my experience, the longest blooming Clematis are mostly found among the smaller flowered kinds. Their myriads of small sized flowers combine to make as exciting a show as any of the large flowered Clematis can offer. I find that their stems and foliage also last more nicely and can be managed more neatly in the garden than is typical among most larger flowered forms.
These details of behavior and appearance are particularly important in gardens that are enjoyed from close up. Long blooming plants are very desirable in small gardens where the number of plants you can have is limited by the space available, and foliage quality matters alot too.
The siting of all Clematis should take into account their not very lovely ankles. Some sort of a nice looking skirting plant located in front will be helpful in this matter. This is not usually for the Clematis to climb onto, but rather to provide a façade for the least lovely parts of your otherwise beautiful vine. Clematis prefer a somewhat shady base, then sun on the flowering parts, so a skirt helps in this also. You need to allow some bed width in anticipation of esthetically needing a skirting partner.
“Grace at the Base”
The support system is a different matter. Whatever support you use, whether living or constructed, you will have to tie your Clematis up a bit every week in the growing season, but you will always get a very generous reward.
Flowering lasts Particularly Long
where Sun and Wind are
Not Too Strong.
CLEMATIS VITICELLA BETTY CORNING
Betty takes first prize for the longest blooming Clematis in my gardens. Her pagoda shaped lavender flowers make her an easy friend in many garden pictures since her foliage is beautiful, and, as Christopher Lloyd was fond of saying,
“Lavender goes with everything.”
She starts blooming in mid June here and continues, in profusion, long after most of her close kindred have gone green again, with some flowers until September.
Each additional year in the ground here has corresponded to an increased length of time that Betty remains in flower. From the 5th year of her residence, she has covered herself with flowers for three months.
It is said that Betty doesn’t get the ‘Wilt’ that can spoil many kinds of Clematis. She is certainly extremely resistant, as I have had the ‘Wilt’ trouble with other Clematis, including some small flowered forms, but never Betty in 14 years of growing her.
The original Betty Corning was the wife of Erastus Corning II, mayor of Albany NY. His father, Erastus Corning the First, was a New York businessman after whom the city of Corning, NY was named, the Corning Glassware Company being such an important business there.
In addition to being an aristocrat, Betty Corning was a passionate gardener. The story is told that one day Mrs. Corning was walking through a steelworkers’ neighborhood and saw a Clematis that was completely unknown to her. It was truly outstanding; an extremely vigorous vine with beautifully shaped fragrant lavender flowers. She knocked on the door and asked about it; the lady of the house said she’d received it from an aunt, “rooted in a potato.” The last detail is rather unlikely, but whatever its origins, Betty Corning asked if she could take a cutting. The lady obliged, and Betty nurtured the cutting and began to propagate it. Several years later when she was in the same area again, she went back to ask for some more cuttings, only to find that the entire neighborhood had been razed for new development.
If Betty Corning had not taken her initial cutting, this Clematis would have been irretrievably lost.*
Knowing the story also helps one remember Clematis Betty’s last name, as Corning Glass comes easily to mind. The plant was named and distributed in the 1930s. This story comes to us through Steve Antonow, a Seattle gardener, as recorded on Kiporos Blog.
Betty overlaps her flowering time with Clematis Crispa, who is extremely long blooming too. Betty is thought to be a hybrid between Clematis Crispa and a Viticella, and luckily Betty seems to have gotten all the genes encouraging a long blooming season.
Also called the marsh or swamp Clematis, this vine is extremely long blooming and graceful. Her small crimped and serrated bells are each perfectly lovely. It is a great thing to bring a vine to maturity, since if you can do this, your crispa will be decorated with these perfect bells for ages each summer, ever afterwards.
Her heritage is from moist places, and so predictably this vine prefers such an ecology. She also needs a lot of space and sun on the flowering parts.
You could choose to have more than one of these as there are color variants from lavender to nearly white, with some bluer and pinker ones inbetween. I have never met one who wasn’t exquisite in its flowers.
This wonderful vine glows with wine red flowers from early July until September. Very vigorous as well as free flowering, she needs plenty of room to spread out horizontally and vertically. As long as she is well supported in her continuing climb, and has space and sun enough for new flowers, she keeps going for three months.
Though she has Viticella blood, her flowers are open faced and quite large (3-5”w) and so make a very substantial impact even at a distance with their rich coloring.
Julia originated in 1900 from a Francisque Morel cross between C. viticella ‘Rubra grandiflora’ with C. ‘Ville de Lyon’ (with C. texensis lineage).
Lost to the trade entirely at the time of World War 1, thankfully it was restored to the English market from a single specimen at Hidcote Manor, in Gloucestershire, and given back its correct name in 1972.
This lovely Clematis flowers with sunny yellow lanterns all along the top of my wooden arch. This structure is the braced frame built originally to carry the children’s swing and trapeze, but now it supports Clematis climbing up from each side, marrying with one another along the top.
Before blooming C. Tangutica has lovely buds you can admire while you wait for it to bloom in early July. After some three to five years in a good place she will typically flower for two months, through July and August, and partially rebloom in September.
This variety has the loveliest seed clusters of any Clematis I have ever met, and so even after flowering, remains so beautiful for a while that I am reluctant to do anything but lightly trim her.
The late rebloom of C. Tangutica often allows her delicate yellow lanterns to accompany the pearly bud clusters and fresh panicles of white flowers of C. paniculata with whom she interweaves at the top of my arch.
As the C. Tangutica display ends, Paniculata takes over the starring Clematis role. Shown climbing the left side of the arch with tangutica, C. paniculata is dressed in her white buds and blossoms by the tail end of August, then for 2 ½ months or more. Lovely in leaf throughout the garden year, once her roots have had a few years to establish, she will be effervescent in white panicles She refreshes the 20 feet of space over which she reigns, at a time of the year when few other perennial plants are providing nascent beauty.
Clematis paniculata will have occasional flowers until it so cold that you must cut her down soon or let her be decorated for the winter in true snow white. Which is fine, if you like the effect. Just trim her down before April or so.
LARGE FLOWERED LONG BLOOMING CLEMATIS
Though belonging to the large flowered group of Clematis, Jackmanii and some of its near relatives are fantastically long blooming after some seasons of establishment.
These, while very satisfying in their blooming habit, have stems and foliage which I find are less easily kept attractive through the growing season than those of the small flowering types.
Most people leave some old wood through the winter on large flowered Clematis vines as they flower the next year on both old and new stems. I have found the need to retain old wood is sometimes a hindrance in the esthetic maintenance of space limited gardens, and so I more usually use small flowered long blooming types that thrive on being cut down to 12″.
If you have a large property, this may not matter as much to you. Perhaps you can have very many kinds, keeping the easily trimmed ones close by and the trickier ones at a distance.
What and Who to Climb
If anyone says that the Clematis don’t harm the things they climb on, I would ask you to be skeptical, and careful in your choice of climbees.
If the shape of the supporting plant character matters to you, and it is a kind that does not spring new wood from the interior readily or is slow to replenish lost parts, you may be sorry to lose the branches that your Clematis could inadvertantly damage.
Whether large or small flowered, and even if the Clematis is a kind that is cut down close to the ground each year, the shade and weight added in the growing season can cause problems for limbs of its supporting companion.
Shrubby plants whose individual branches are unimportant to their overall good appearance can be good choices as climbees. I would try for a well grown specimen before asking it to support a Clematis companion.
If you want something which is evergreen, Yews are a very good choice for support because if any portion of their wood is harmed it will soon be replenished by new growth from a nearby shoot, even, as needed, from within its interior structure. Not many evergreens can do this trick well.
Because of the different soil needs of Yews and Clematis, the vine should be physically planted so its crown is at a bit of a distance from the Yew so as not to be affected by any local treatment of the soil meant for acid loving things. Over time you may want to give your evergreens some Hollytone™ or other acidifying agent, and your Clematis won’t like that if it’s close by or downhill.
To keep my Clematis going as long as possible at a height I can manage and enjoy, I may wrap the Clematis tendrils around and around things that are in their climbing paths.
The Clematis discussed herein seem inclined to flower longer and better if the vine can keep growing along. A support system like a trellis or wire system is needed for vertical climbs, and wraparounds are a space saving way to keep them recurrently flowering in the horizontal plane. One can wrap around any artifacts placed in their paths to keep them elongating. This wrapping works nicely, for instance, around the bases of the planted tufa containers residing at the tops of stone walls. Well supported or encouragingly wrapped, most all of the Clematis do their best work when tied and tended.
 Steve Antonow, Seattle Gardener / ref Kipouros blog/
 Brewster Rogerson : http://www.clematisinternational.com/page69.html