Heleniums are easy plants to propagate. While many herbaceous plants can be divided in the autumn, heleniums are an exception and are best dealt with in spring just as they are starting into growth. You may get away with autumn division with a large clump but the distrubance followed by a cold wet winter will often kill smaller pieces.
The simplest method is to tear apart an established clump into as many pieces as necessary. As with many border plants, the material growing on the outside is the most vigorous and the best to use. Wait until growth has started - this, in western europe, is probably from mid March onwards.
A plant at just the right stage for division - growth has started but stems have not lengthened too much - some new root growth has started.
You can divide as small as you like right down to a single rosette with its roots. As you divide it is easy to separate and remove the old and dead material which was the previous year's growth. It is easier to separate small pieces if the plant is washed in water.
While division is the most straightforward and effective method of increasing and exchanging plant material, you can also take stem cuttings to increase your stock. These can be either stem tip cuttings or one or more or nodes of stem. When propagating by cuttings, sterilise knives and secateurs between varieties to avoid cross contamination.
You will need the controlled conditions provided by a mist unit or a closed case plant propagator to be succesful but rooting is reassuringly fast and rooted cuttings are best potted on quickly! Whichever type, it is important to take them before early summer (about mid June in northern hemisphere) so that they are large enough to survive the following winter.
Ready, steady, root! Soft stem cuttings taken from rapidly growing shoots in spring, root very quickly. On the left, the cutting as taken from the plant. Note enlarged stem base on centre plant and right just two weeks or so after taking the cutting the new plant is almost ready to pot on. You will need bottom heat and either mist or shade and polythene for success.
You can also grow heleniums from seed and even get flowers the year they are sown. There is no chill requirement so seed can be sown in early spring - say late February or early March in N Europe given greenhouse or cold frame protection. Prick out when large enough to handle. You will not get the same plants as the parent so you cannot call them by the parent's name. If you've got the space then why not grow on 100 or so and select the best ones. That's how new varieties are produced after all!
Wild heleniums are found growing in a wide variety of conditions but very often in moist or even wet habitats. The garden forms also show a preference for damp conditions but will tolerate any soils except very dry ones. We grow them on heavy clay with success. If soils are dry it will help to include plenty of well rotted humus to retain moisture.
Heleniums are very hardy with H autumnale being the most hardy of all. Many of the forms in cultivation are derived from this plant - they tend to be the forms with a sawtooth edge to the leaf and which start early into growth and stem elongation in the spring.
Taller forms may require staking especially when grown on damp or fertile soils. Dead heading of the flowers will extend the flowering season. Once flowering has ceased and the plant has died back the stems should be cut down. At this stage many varieties will have next season's shoots visible at the base of the plant. Do not be tempted to lift and divide them in the autumn but leave until growth is just starting in the following spring.
To maintain vigour, many varieties will benefit from dividing every three or four years - lift the whole clump as growth is just starting in early spring and prize off the most vigorous parts from the outside of the clump and replant them. A garden fork or two used back to back if the clump is very dense, will do the job quite well.
Pests and Diseases are mercifully rare in Heleniums. In early spring the soft new growth can be damaged by slugs - some varieties seem more prone than others. For long term control I thoroughly recommend the use of surface mulches of chopped or shredded twiggy material. This not only acts as a physical deterrent to slugs, more importantly it provides an excellent habitat for those fast moving small black beetles which are superb slug predators - in particular slug eggs. It will take some time to build up a population and in the meantime, if you have to resort to pellets, put a small number of them - and you do not need very many- under a slate similar to keep birds away from both pellets and the poisoned slugs.
Viruses are sometimes found. According to the RHS there are two of concern - H. S Carlavirus (HSCV) and H. Y Potyvirus (HYPV). HYCV is, apparently, normally symptomless on its own and is transmitted by aphids. HYPV causes leaf chlorosis, flower distortions and stunting; it is mechanically transmitted. I have seen stock for sale in the UK which has been badly diseased - any suspect material should be destroyed immediately. The presence of both viruses together makes symptoms worse. Never buy or propagate from material showing distorted flowers and if the leaves are mis-shapen then try and identify the source of the problem.
In assembling a Helenium collection I have gathered plant material from far and wide. A few specimens have developed symptoms of leaf and flower distortions which appear to be cleared up by taking small stem cuttings in spring. I suspected nematodes and sent samples to the RHS for investigation. Nematodes (stem and bulb eelworm) have been found. Destroy plants by burning which show symptoms such as flattened and thickened stems, untypical thin willowy or distorted leaves and misshapen flowers. If you must propagate (to avoid losing a particular variety for example) then select the least affected material and monitor the new growth carefully. Warm water treatment of the dormant roots (43.5oC) for 1 hour is reported to kill eelworm.
I am having some success in taking very small cuttings off the top of growing plants in early spring, growing them rapidly and then taking small cuttings from the tops of these plants. This can be repeated in subsequent years. There have been undoubted improvements in flower quality and vigour by this method and I am now going through the least healthy stock in the national collection and cleaning it up in this way.
Growing conditions at Wisley are far from ideal but, even on light sandy soil, Heleniums can perform well if given adequate moisture. This is the 1998-2001 trial plot , photo taken mid August 2001. The trial has now finished but the best varieties (awarded an AGM) have been replanted for further display.