A compost into which rooting can take place can be prepared from 3 parts sphagnum moss peat (do NOT use sedge peat as this can often have a high pH) and one part of horticultural perlite. An acid gritty sand can be used instead of perlite where available but it must be acid. This applies even for the propagation of heathers which would normally grow in any soil, as an acid medium will improve the rooting yield. There is no need to add fertiliser at this stage, in fact, the yield is likely to be higher if none is added.
If horticultural perlite is being used add water to the perlite as instructed by the manufacturer, otherwise for easy mixing and subsequent handling, there is no need to add extra water at this stage.
Heathers can be propagated by layering, cuttings, or by seed.
To increase your stock of heathers, they must be propagated vegetatively to remain true to the parent plant. Heathers produced from seed, even from foliage cultivars, will vary considerably, from ones indistinguishable from moorland plants to perhaps a new find unlike any available commercially. However, there is more chance of winning the lottery than obtaining a truly different plant!
Propagation from seed is often used where heather is needed for restoration work or for such areas as golf courses. Heather seed can be triggered by fire and light, so germination is increased if the seed is heated to 120ºC for 30 seconds before sowing in the propagation compost. Recently it has been discovered that in addition to the more obvious effect of heat, the smoke from fires is responsible for stimulating the germination of seed of many Erica species in South Africa. It is thought that this effect would hold true for hardy heather species as well.
It is now possible to obtain a primer solution containing a combination of natural substances which have been found to overcome dormancy and stimulate seed germination. It takes the form of an impregnated paper disc which can be obtained from Kirstenbosch National Botanical Garden, Claremont 7735, South Africa.
This is the simplest and most reliable method for the gardener who wants just a few plants of a particular variety.
A layer can be made at any time of year. Nine to ten months later a root system will have formed at the bend in the stem where it was pegged, and the new plantlet can then be severed from its parent and planted in its final growing position. Several such layers can be made around the plant without affecting its appearance.
A development of this technique is to dig the plant up, make the hole considerably deeper and re-plant so that only the growing tips show above the soil. These will produce new roots and can be severed from the old plant after about 6 months.
The most common method of producing heathers is from cuttings. Many gardeners have trouble rooting heathers from cuttings but if a number of simple rules are followed, a high success rate can be achieved.
What happens when a cutting roots? Why do some species root easier than others? Why do cuttings root easier at certain times of the year? These questions and many others like them arise irrespective of what form of propagation is used.
Rooting depends upon many inter-related factors, some beyond our control, but other aspects are helpful in determining the type of material we should select. In general, cuttings should be taken from healthy, vigorous plants, preferably not more than three years old, but other aspects are more species-dependent. There is no need to use rooting hormones for hardy heathers.
Calluna vulgaris cuttings can be taken in April using the leafy growth appearing above last year's flowers. In this case, select stems where the leafy growth is at least 1cm long. Cut the stem with a sharp knife 2cm below the leafy growth. Remove any dead flowers by rubbing your finger and thumb down the stem.
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Preparation of Calluna vulgaris cuttings in April |  |
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Calluna vulgaris cuttings can also be taken during July and August from the growth just below the flowering stem. Select stems which are firm and just turning straw brown. Discard stems where the leaf nodes are more than 2mm apart as these will be more difficult to root and make a less shapely plant. Cut the stem with a sharp knife immediately below the flowers and then cut again to create a cutting 4 to 5cm long. Remove the leaves from the lower 2cm of the cutting by rubbing your finger and thumb down the stem.
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Preparation of Calluna vulgaris cuttings in July |  |
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Calluna vulgaris perhaps gives us the easiest clues in establishing how and when rooting occurs. A film would show that one or two weeks after the cuttings have been inserted, the leaf nodules below soil level begin to swell. Days later a split starts below the nodule. The split increases in length as the nodule continues to swell. The swelling induces more splits around the nodule and in particular causes a small split directly above the nodule from which the root emerges. This is contrary to most plants which root around the edge of the wound (caused by the separation from the mother plant). One layer of tissue which a root must rupture is known as the sclerenchyma and probably the root has to wait for this layer to be split by the swelling nodule before rooting can occur. In time, many roots appear from the splits. Easy splitting and multiple rooting could account for why most propagators find Calluna easy. There is a marked tendency for the splitting to occur first towards the base of the cutting. On occasions it is possible to observe all stages occurring simultaneously on one cutting. Thus if propagation is under good control, the longest roots will appear close to the base of the cutting (but not around the edge of the wound, where the cutting was separated from the mother plant). Others, less long, can be observed as you approach the surface of the soil. When propagation is not under control, often weak rooting will appear near or at the surface of the soil. The normal cause is that the soil is too wet but cuttings from old wood will also show this effect.
Daboecia cantabrica and Daboecia x scotica cuttings are best taken in July. Select side shoots which are firm and just turning to straw brown about 4 to 5cm long. Pull down carefully to tear the cutting from the main stem so as to leave a small 'heel' at the base of the cutting. Remove the leaves from the lower half of the cutting by pulling downwards. Sometimes this type of cutting is not readily available, in which case prepare in a similar way to a July Calluna cutting.
Erica carnea cuttings are best taken in July or August by selecting stems which do not have buds forming on them. Ideally heel cuttings about 4 to 5cm long are best but if in short supply a tip cutting can be prepared but cut off the top 5cm of growth with a sharp knife. Avoid stems where the leaf nodes are more than 2mm apart. The lower half of the leaves should be removed by rubbing a finger and thumb downwards along the stem.
In the case of the heel cutting, nip out the growing tip. As Erica carnea flowers profusely, it may be difficult to find cutting material without buds, in which case these will have to be used. Prepare as above but remove all flower buds by rubbing a finger and thumb upwards along the stem.
Erica carnea cuttings can also be taken in March and April. At this time of year use the top 5cm of growth but do not pinch out the growing tip. Nature has already provided a number of embryo shoots, more in fact than you can create by pinching out the tip.
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Preparation of Erica carnea cuttings |  |
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About two weeks after the cuttings are taken, a gradual swelling of the whole stem is observed. After three to four weeks roots always start to form above a leaf nodule. After about ten weeks, more roots can be observed coming through the callus formed over the nodules. These tend to be rather weak compared to the other roots which are well developed by this time.
Erica cinerea cuttings are best taken during July and August, using non-flowering heel cuttings. If available, these are likely to be quite small, 1 to 2cm long. Remove the leaves from the lower half of the cutting by rubbing finger and thumb down the stem. Often heel cuttings of this type are difficult to find, in which case the stems below flowering shoots can be used, provided the spacing between the tufts of leaves does not exceed 2mm.
Cut these from the plant in a similar way to that described for July Calluna cuttings, but as roots usually only appear from the base of the cutting, make sure the lower cut is made immediately below a tuft of leaves. Remove the leaves from the lower half of the cutting.
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Preparation of Erica cinerea cuttings |  |
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This species roots by producing a large swelling at the base of the cutting (it does not seem to matter whether it is a tip or heel cutting). The time it takes to do this varies considerably. Roots appear two to three weeks later. It only rarely roots around nodules, which may account for the increased difficulty most propagators have with this species.
These species root in a similar manner to Erica cinerea.
Erica ciliaris, Erica mackayana and Erica tetralix cuttings are best taken during July and August using non-flowering heel cuttings about 1 to 2cm long, which are usually plentiful. Remove the leaves from the lower half of the cutting as described above.
These species root in a similar way to Erica carnea. Interestingly, Erica x williamsii behaves in a similar manner to Erica tetralix despite the leaf attachment being closer to Erica vagans.
Erica x darleyensis, Erica erigena and Erica vagans cuttings are best taken in August, making particularly sure in the case of Erica erigena that the stem is semi-ripe, i.e. firm and turning to straw brown. Take and prepare heel cuttings 3 to 5cm long as described for Erica ciliaris.
Once a cutting has been severed from the parent plant, it will continue to loose moisture via the leaves until such time as it produces roots. The two basic ways of rooting heather cuttings attempt to keep this transpiration loss to a minimum. The first, open to all amateur growers and described below, relies on keeping the cuttings humid, the second is more sophisticated; mist propagation.
This method relies on keeping cuttings humid to minimise transpiration and is suitable for rooting most of the widely grown hardy species of heather. There are many adaptations of this method, depending on whether small or large quantities of rooted cuttings are being produced.
The main danger with this approach is the risk of fungal attack. If small numbers are required, the following method minimises that risk
If slightly larger numbers required, the twin pot approach can be replaced by a plastic seed tray. Lightly firm compost into the tray and dib holes 2cm apart. Follow steps 5 to 8 above.
Leave for several months, checking occasionally that the polythene bag is fogged. If not, simply heavily water again, leave 20 minutes and re-seal. Any cuttings that die should be removed to minimise disease.
This method is slightly more prone to fungal attack and therefore is most effective if propagation is delayed until September.
Many large heather producers use this approach on a commercial scale, placing plug trays on heated beds with shallow sides. Polythene sheet is stretched across the bed and is turned every 3 or 4 days to minimise fungal attack. The cuttings are routinely sprayed with a non-systemic imidazole fungicide.
Care has to be taken to wean the cuttings from the humid atmosphere once rooted. On dull days, the polythene cover should be lifted slightly for an hour to start with, gradually increasing the period until the cover can be completely removed.
The rooted cuttings can either be potted on or planted out in a nursery bed.
Transplanting is best done in early spring, but if the cuttings are sufficiently well rooted by September, they can be potted on and over-wintered in a cold-frame.
Knock the cuttings out of the seed tray in a similar manner as one would a plant from a pot. Divide the cuttings from each other using an old knife.
Place the relatively dry compost into a 9cm pot (smaller sizes are more prone to drying out) and lightly firm. Make a hole in the centre of the pot and plant the cuttings deeply, burying any bare stems so that the lower foliage rests on the soil surface. Make sure that the cuttings have been firmed in well. Water heavily and place the pots outside in a well drained, not too exposed area.
If the nursery bed approach is adopted, prepare the ground well, removing all weeds and adding sufficient grit, acid sand and sphagnum moss peat to create a fine tilth. A dressing of general fertiliser such as John Innes base at 55 grams per square metre will help to produce strong healthy plants.
Water regularly throughout the spring and summer. Rapid growth will be made, so, to ensure a shapely plant, prune all Erica carnea back to 3cm to 5 cm at least once during the growing on period.
For most cultivars, rooted cuttings transplanted in spring should be ready to be planted out in their final positions by the following autumn but some Erica carnea cultivars may need another growing season.
Use a proprietary ericaceous compost mixed 2:1 with horticultural perlite. The important feature to look for when purchasing compost is to ensure that it is suitable for ericaceous plants.
Alternatively, the compost made up for propagation of cuttings can be used (this time there is no need to sieve the peat). If this approach is taken, a weekly supplementary feed will be required using a proprietary liquid tomato fertiliser.
With peat becoming a diminishing resource, a considerable amount of research is being conducted to find an alternative to peat. Peat-based composts have been optimized over a number of years and a complex science has developed describing how nutrient and water holding capacity are determined in such media. Several alternatives are being pursued and no doubt more will be investigated, but at present, composts based on coconut fibre or wood fibre are unsatisfactory.
© The Heather Society, 1 December 2006