Making New Clematis From Elderly Container Plants
Long Division: Making New Clematis From Elderly Container Plants
by Linda Beutler, curator
At the Rogerson Clematis Collection there is hardly anything more satisfying for a volunteer to learn than how to save an ailing old containerized clematis from certain death, and to end up with several rejuvenated plants when you started with one.
It is now pretty widely known that until its arrival at Luscher Farm, the Rogerson Clematis Collection plants were all grown in containers, and housed in poly-covered houses at a wholesale nursery. For the largest part of the collection’s life, Brewster amassed the plants in isolation, with only limited help from work crews at the nursery when manpower for extensive weeding or pruning was necessary. Brewster did the daily tending—watering, fertilizing, grooming, repotting, root pruning—himself. Remarkable, when you think about it.
When Brewster did recruit volunteers, the initial charge for all of us was to help get the collection back into shape by pruning, tying up, isolating seedlings, and figuring out, where possible, why some clematis entered a sudden and precipitous decline. Brewster always insisted on the same process, to haul sickly plants to the potting bench to “have a look inside”. He instilled in all of us a certain fearlessness for examining clematis roots, and we, in turn, came to understand the alarming if distinct life-cycle of clematis kept too long in containers.
You see here an image of a soil type we call “wet chocolate cake.” After two to three years in the same pot, even the best potting soil will decline to this state. Over time soil structure breaks down. Small particles hold water without admitting air because larger chunks, bark or perlite or pumice, degrade as water continually passes through them. Peat-based soil is particularly notorious. Drainage becomes poor.
Should soil in this state dry completely, the only way to rehydrate it is to plunge the container into water and soak it until it sinks. Without plunging, the water will flow down the outside of the root ball, next to the pot wall. If soil in this state is already thoroughly wet, the result when watering is the same, the only sharp drainage is at the outer edge of the root ball. In either case, the clematis roots flee the center of the soil, and grow to the edges, working their way around the interior pot wall, where they are vulnerable to overheating if sun shines directly onto the pot. Now you have “twice-cooked clematis,” steamed if too wet and hot, fried if too hot and dry.
The behavior of a large-flowered hybrid, viticella hybrid, or most atragenes (C. alpina, macropetala, and their cousins and hybrids) in this type of soil environment is predictable. Clematis show the first stages of decline by abandoning old wood (which planted in a garden might live, becoming trunk-like, for 10 or 20 years) and producing a proliferation of spindly new growth, perhaps even displaying a mass of smaller than expected blossoms. This can be impressive, like the last beautiful aria of Tosca. Each scrawny stem usually represents a new crown, produced just below or at the soil surface. This is the plant’s attempt to create new growth nearer a hospitable environment. Often the roots of these new crowns emerge to the surface, run to the edge of the pot, then down the sides, where water flows and the air-to-water ratio is better. The interior roots of the plant are rotting.
If unnoticed and unattended, the clematis has less than a year to live. This may sound overly dramatic, but there it is. These young crowns are not likely to survive the next winter. The unrelenting soggy soil, coupled with cool temperatures, will spread the interior root-rot throughout the soil. The proliferation of crowns is a last attempt to live.
Clematis with nothing left but surface roots are more susceptible to being choked by weeds. As we work through the collection, attempting to control tenacious weeds such as oxalis and violets, we can assess the overall health of a plant by a few telling characteristics. If we move the pot and it is bottom-heavy prior to being watered, the soil is holding too much water and may be failing. If a plant we know to be big and boisterous is suddenly sparse and new growth lanky, we know what we’ll find if we tip it out of its pot: wet chocolate cake. If roots and crowns are visible at the surface, the clematis wants immediate help. NOW!
We follow these steps when treating such plants:
1. Prune the clematis back to 12 to 24 inches tall. Remove any damaged leaves. Ailing clematis often show sunburn when they never did before. This is another diagnostic indicator.
2. Remove the signage on the plant and set it aside.
3. Supporting the stems at soil level between outstretched fingers, with the other hand tip the plant nearly upside down and slide it out of the pot.
4. The soil will look and feel like wet chocolate cake, and will smell rancid, moldy, and in extreme cases will reveal patches of white mildew.
5. Sometimes the soil may fall away when you shake the crown, but usually it sticks like glue. Work as much of the soil off the roots and crowns as you can. Pointed chopsticks are invaluable for this purpose.
6. Once you have removed as much soil as you can by this method, it is usually also necessary to bath the roots to remove the final coating of soil so that all crowns are clearly visible.
7. Pull away any obviously rotten or disconnected roots.
8. If the root mass is, in its entire state, fairly full and long, cut the roots back by not more than about a third their length. If the root mass it skimpy, do not prune at all, and try to salvage as much of it as you can as you go to the next step.
9. Start wriggling the crowns apart, starting with those around the outer edge of the original crown, and working toward the center. You will damage a few roots, and roots rotten at the crown will pull apart. Don’t be brutish, but extreme gentleness is not required. It is amazing how much inept manipulation these plants will tolerate.
10. It may be necessary to clip crowns apart from umbilical-like cords of old woody crowns. Just make sure every new crown you separate has a nice tuft of roots of its own.
11. Once in a while two crowns are so closely linked and intertwined that they cannot, and maybe should not, be separated.
12. Once all of the crowns are apart, prepare new labels for each, and decide what size container each should go into. Use fresh, free draining potting soil. You also have the option of taking two or three small crowns and potting them together. Finish with a drink of transplant liquid, half strength, or a light soil application of slow-release rose and flower food.
13. DO NOT OVER POT, meaning placing a new plant in a pot much too large for it. It will stay too wet in soil it doesn’t have enough roots to exploit. Likewise, do not plant newly divided clematis directly into the ground. Let them live in a pot until their roots fill it up, which may take four to six weeks.
In the final image, you see the results of a morning’s work, and how many new plants were created from five desperate clematis. The plant shown being divided, by the way, was ‘Maria Louise Jensen’.
