I.Cl.S. - The propagation of Clematis from cuttings - a discussion of some causes of failure
This web page has been re-produced from an article from The International Clematis Society Journal 1998 by Tom Bennett, edited by Fiona Woolfenden. Either read the whole article or go straight to the section of interest using the following content list.
Clematis have the reputation of being difficult plants. The notion is widespread enough, when applied to cultivation and pruning, to make amateurs think that propagation is impossible unless practised by the most skilled and experienced professionals. By explaining some of the ways which would-be propagators fail, and the reasons behind some of the genuine difficulties of propagation, I hope to clear away some of the mystique that currently surrounds the subject.
Material for cuttings
As with many other plants, the best material to use for softwood cuttings is that, taken early in the year, from 1 year old plants grown under glass. It is vigorous, likely to be free from pests and disease, compact and therefore easy to handle. In an unheated greenhouse in the UK, we would expect sufficient growth on stock plants to be able to take cuttings in mid-April. By starting this early, we can rely on a growing season of six months or more which will produce stronger, more mature plants by autumn and the number of winter casualties will be reduced.
By contrast, any attempt to take cuttings from plants established outside will have to wait until late May for suitable material to develop and, in the case of some cultivars, and plants grown in colder areas, as late as mid-June, Also, without glass, the propagator has less control over poor weather, late frosts, pests and disease.
Although all species and cultivars will root from softwood cuttings, it has been found that certain species can be struck from hardwood material. This is taken between late February and April, before the dormant buds break. It is immaterial whether the stock plants are grown outside or not. C. montana, C. chrysocoma (and their derivatives), C. x jouiniana and C. heracleifolia all root well by this method but there may be others. I have known the large flowered hybrids root this way, but only occasionally. It is interesting that they will root poor results on our part may be due to faulty technique which could be improved if. we cared to experiment. It is not generally appreciated that the amateur is far better placed in this respect than is the professional, for whom time spent on research means money (so too does a failed experiment). This means that commercial growers tend to stick to tried and tested methods, leaving the field free for the dedicated amateur.
Not all shoots are suitable for use as cuttings, even though they may look it. Nodes which contain flower buds in the axils will root but often fall to produce shoots and should be avoided It is easier said than done with some cultivars: C florida Sieboldiana and C. x Aromatica, in particular, produce little but flowering wood and for this reason alone are difficult to propagate. Sometimes cuttings will go blind for no apparent reason. Botrytis, flower buds and the bud drying out have all been suggested as the cause, although I would question the basis of the last one.
I can't leave this section without mentioning C. Perle d'Azur. A highly desirable clematis, It is always in short supply. Commercial growers will tell you that It is hard to propagate and yet you will find that it roots with ease. The problem here is the remarkably long distance between the nodes (50 cm is not uncommon) which means that for each stock plant, a grower may get only 10% of the cuttings he might get from the average clematis cultivar.
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Preparation of the cuttings
Softwood internodal cuttings are easily handled and are economical with material, The shoot tip is too soft but stem below this which is still green (or bronzy) is ideal. If older, hardened wood has to be used, it should be wounded by removing a thin sliver of rind from one side. As shown in the diagram, cuttings consist of one node, a leaf or leaflet(s) and about 5 cm of internode below. All cuts must be cleanly executed with a sharp knife or razor blade (watch your fingers!); ragged cuts will encourage fungal disease, The cut at the base of the internode must be immersed in water immediately; if it dries out the cutting may look fine for weeks but will be reluctant to root. How much leaf to remove is a matter of judgement. The principle is one of leaving the maximum possible, just short of causing the cutting to wilt subsequently from excessive transpiration. Wilting, even for a few minutes, will damage the leaf permanently and weaken the cutting. Before striking, the cuttings will benefit from a quick dip in a suspension of fungicide. Return to content list
Types of cuttings
Hardwood cuttings can be either inter-nodal or nodal and benefit from being wounded at the base as shown in the diagram. Some believe that wounding should be practised on all cuttings. It certainly encourages callusing which is a precursor to roots. Though not feasible for commercial producers, the time it takes may well reward the amateur who propagates small numbers.
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Striking the cuttings
A free-draining compost capable of some moisture retention should be the aim. 50% moss peat 50% sharp medium grit is ideal. A standard seed tray is filled with the mixture and is topped-off with horticultural sharp sand to discourage disease. A common mistake is to use too much peat or to substitute sand for grit. Compost made this way will become soggy after watering and will encourage rot. The compost should be lightly firmed but not watered until after the cuttings have been inserted. Delaying watering means that the cuttings can be pushed into the compost more easily (don't use a dibber, you shouldn't need one) and the mixture consolidates well around them, avoiding air pockets. Overlapping leaves quickly develop botrytis so keep them to a minimum. Don't worry about a little overlap, though - it is fascinating to see how the leaves re-arrange themselves over a couple of days so as to take full advantage of the available light.
Rooting powder does no harm and those which contain a suitable fungicide will help to prevent stem rot. Use in line with the manufacturer's instructions. 0.5% IBA. is recommended for softwoods; for hardwoods use a stronger formulation.
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Care of the cuttings
Hardwoods are easy. They will take moderate frost so, in the UK, at any rate, no heat is needed. Steer clear of close polythene or too much damping down (both encourage botrytis) until the buds break. By this time, rooting should be under way. Use fungicides once a week when you water and shade against strong sunlight When the buds open, syringe as necessary to prevent wilting.
Softwood cuttings need much more attention. They are dependent on their leaves and a fine balance should be struck to allow the maximum light levels whilst preventing scorch. Too little light will prevent rooting as will the loss of the leaf. A most effective way round this is to mask those panes of the greenhouse through which direct sunlight will enter, with a proprietary liquid, brushed or sprayed onto the glass. Failures happen when insufficient shading is used or the shading misses areas through which direct sunshine passes undetected, as might happen, for example at 7.00 each morning, a time when you might never be in the greenhouse to notice. Be mindful too of doors and ventilators through which the sun will penetrate, unhindered and unnoticed for just a few damaging minutes each day. Don't overdo the shading by applying it everywhere; the cold light that passes through north facing glass does nothing but good and should be allowed to fall onto your cuttings unhindered.
Polythene applied closely over newly-struck cuttings, in order to reduce evaporation and stop wilting, causes the high humidity ideal for fungi and should be avoided if at all possible. Heat can also build up under it particularly if your shading is inadequate, and it is common to see cuttings cook as a result. It is far better to position it so as to allow some air movement around the cuttings and to remove it completely at night to allow their leaves to dry out. After about ten days you should be able to dispense with it completely, providing you still spray the foliage at regular intervals (the frequency will be dictated by the weather) during the day.
Heat from electric soil warming cables, controlled by a thermostat speeds up the process of rooting. By using a bottomheat of 23 degrees C, roots should form within 14 days, without it depending on the ambient temperature of the greenhouse, you might have to wait 40 or more. With bottomheat though, your compost will dry out from the bottom upwards so watch the watering; a container that is soaking at the top will, with insufficient watering, be dust dry 4 cm further down.
Fungicides should be applied once a week. It is important to use at least two different types, in rotation. There are a number to choose from. The idea is to keep the various strains of botrytis guessing and to knock out those types that are resistant to any one fungicide. Botrytis is cunning, though. It usually sneaks in under the leaf canopy which will then begin to collapse in big holes full of brown leaves covered with white, fluffy fungus. Most likely, the day before, a superficial look would have revealed nothing. Cuttings affected in this way will be a total loss even if they have begun to root. Get into a habit of combing through the leaves, gently with your fingers (like you might look for fleas on your cat!). Do this every couple of days and remove all affected leaves immediately: botrytis can spread like wildfire.
After 3 weeks with heat or 5 7 without, your cuttings will need less and less water on the leaves although still plenty at the roots which will, by now, be forming nicely Wean the cuttings as you might harden off seedlings in your propagator. They can be given more air and less heat and, if you are using a thermostat, reduce it by, say, 2 degrees C steps every 2 days until you have reached ambient greenhouse temperature. The process will take a week or ten days.
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When the roots are 6 cm long or more or when a shoot is growing strongly from the node (be careful, some cultivars produce small, weak shoots long before they root), you can pot up. This helps to keep up the momentum of growth needed to establish a strong plant for the coming winter. Use the correct grade of compost (the weakest). It is a mistake to use a strong compost rich in nutrients (e.g. John Innes No. 3) as this will scorch the new roots. Another common mistake is to over pot. Far better to go via 0.31 to 1.01 then 2.01, making sure that the roots at each repotting have used up most of the compost provided by the previous one. Pot a new cutting straight into a 2.01 pot and you will most likely lose it.
Adequate watering, shading from strong sunlight, protection from wind and cold nights (by ensuring proper hardening-off when the potted-up cutting makes the move from greenhouse to outside), and wilt prevention are all needed to carry the cutting through its first summer and autumn without undue check.
Don't plant out the large-flowered hybrids until the second summer, they are best protected over the winter in a greenhouse or frame. On the other hand, some strong growing species (C. montana and C. tangutica and their derivatives for example), together with the viticella cultivars will, if struck early enough in the UK, be ready for their permanent positions by the September of their first year.
Finally, it is worth stressing that all clematis, struck as softwood cuttings under optimum conditions and with the right treatment will begin to root in less than 4 weeks. C. tangutica and C. orientalis can be potted up a month after striking and I have done the same recently with C. Sir Trevor Lawrence in under two months, despite it's reputation of being a devil to propagate. Naturally, failures will continue to happen with us all but these are due to our mistakes, not (as we may often like to think!), an inherent stubbornness in the Genus.
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P.S. Tom then gives some tables to assist in identifying common errors in propagation by cuttings, by detailing the 'ERROR' and the 'SYMPTOM(S)'. There are only a few copies of the 1988 Journal left. So if you would like your own copy of this interesting article please join the International Clematis Society and send me an email asking me to reserve you a copy. I will send you this journal as your complementary old Journal on joining the International Clematis Society.
Details of how to join are available on the Web page How to Join.
If you are already a Member of the I.Cl.S. see the Web page detailing how to buy copies of Old Journals.
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