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Growing Darwinia....Grafted for Reliability

Doug McKenzie

We live on a fairly flat block 0.6ha (1.3 acres) in area, 1km inland from the south coast of Victoria at Ocean Grove. The soil is acid and consists of a shallow layer of medium-heavy loam overlying sticky orange clay at about 0.25-0.33 metres (10"-12") depth. Sometimes a layer of stony nodules lies at the junction of the two layers. Drainage is fair, but some areas that have been planted lie in a hollow and remain wet for a long time after heavy rain. The natural vegetation, which has been left around most of the perimeter, consists of an open Eucalyptus woodland type vegetation, the main tree species being the swamp gum, E.ovata, and the yellow gum, E.leucoxylon. Annual rainfall would be about 60cm distributed through the year with a winter maximum. Frosts occur rarely.

The garden, the oldest parts of which are about 18 years old, has been planted mainly on the north side of the house in a fairly large area initially cleared of taller trees to allow plenty of sun. This garden area is protected from wind by the house and surrounding natural vegetation, a mixed blessing when growing plants that are prone to fungal troubles. Quite a few garden beds have been built up in height using mostly straight ungraded scoria, which was cheaper than sandy loam.

The first grafting experiments were with Banksia, a few of these plants still surviving, just hanging on as dwarfed or stunted specimens. Considering the time spent and the number of plants grafted, the results were disappointing but the grafting of other genera, Hakea, Swainsona, Grevillea and Eucalyptus followed. The small plants in the Myrtaceae had always interested us, and I remember hopefully trying some early grafts of those notoriously difficult genera Verticordia, Hypocalymma and Darwinia onto a whole range of easy to grow plants from other genera in the Myrtle group such as Melaleuca, Thryptomene and Astartea. Needless to say most of these failed as the combinations were hopelessly incompatible. In the end the rootstock that showed the most promise was Darwinia citriodora. Many of my oldest grafts using this rootstock are still alive after 17 years. It is a graft rootstock for our conditions, being very tolerant of both wet and very dry conditions. It has been successful as a rootstock for Darwinia, Chamelaucium and Actinodium. With Darwinia, the resulting plants are much more vigorous, even more robust than those in their natural habitat.

Grafted Darwinia, such as Darwinia meeboldii, have proved to be the great success. Select the thumbnail image or plant name for a higher resolution image (24k).

However, it is a mistake to regard grafted plants as cast-iron "super" plants that can not die. Solving root problems is very important but is not the only limiting factor that dictates the survival of our plants when introduced to horticulture. It now has a hardy root system, but the foliage can still suffer from foliar diseases if grown in a humid, poorly ventilated spot. Probably the most reliable results can be expected from plants growing in full sun in the open ground.

Planting Out Grafted Darwinia

Because these plants have been grafted using a micro-grafting technique when the plants are very small and young, the graft union is quite close to the ground. When planting out, make sure that the plant is planted at the original level so that the graft union is clear of the soil; in fact it is best to mound the soil surface slightly so that there is no danger of the graft being covered as the plant matures. Some of the topmost roots may be slightly exposed. This is deliberate, and should not cause concern as these will soon wither as the stem increases in diameter. Try to avoid staking when planting out.

Darwinia oxylepis, is one of the most attractive of the "mountain bells" . Select the thumbnail image or plant name for a higher resolution image (24k).

If the plant can be planted in an open, sunny, moderately well drained position, few problems should occur. I think that one aspect of growing Darwinia, whether grafted or ungrafted, that is often overlooked is their need for air movement. The mountain environment from which most of the 'bell" species come is windy, not just the freezing cold southerlies that may bring snow in winter or a sudden cold southerly change in summer days. If growing in a garden, it is tempting to position them in a hot dry position, perhaps facing north, protected from wind by a fence or wall or perhaps growing them in a pot in a protected courtyard or on an open verandah. Plants planted in this situation in our garden, we have noticed, are the first to show signs of fungal trouble, powdery mildew, or partial leaf drop. Plants free of these diseases are those fully exposed to our prevailing cool winds, even plants growing in filtered sunlight rather than full sun.

Avoid "pushing" the plant with too much water or overdoses of fertilizer, particularly when the plant is young . Do not pamper the plant.

They may also be grown in a container. Use a good quality potting mix that is suitable for native plants. If the plant has been growing in the container for a long time, or is not in active vegetative growth, do not over-water but allow the soil to dry a little between waterings and make sure the container is sited where the plant gets plenty of sun and air circulation.

Pests and Diseases

Some species may be disfigured by powdery mildew after warm moist spells, particularly if the plant is growing in a sheltered position. A white powdery deposit is seen on the upper leaf surface. Leaves may go black and drop off. Solutions are to grow the plant in a more open situation, or to spray with one of the proprietary Rose sprays - these usually contain Triforine which is most effective against powdery mildew.

Other fungal problems sometimes cause leaf drop of older leaves, or spotting of the foliage - particularly after lengthy damp periods. The best solution to these problems is to place the plant in a better ventilated area. If leaf drop occurs, keep the plant dryish if possible, until new leaf growth begins.

Coming from the colder peaks of southern Western Australia, most species are frost and cold hardy - indeed some species seem to need cold weather to set flower buds. Very severe frosts may, however, cause burning of developing flowers on some species.

Keep an eye out for the usual plant pests. The highly aromatic foliage does seem to discourage most pests, but watch for insect damage to buds.

Species Available as Grafted Plants

Darwinia macrostegia (Mondurup Bell)

The form being grown as a grafted plant is incredibly floriferous. One garden plant that is about 10 years old has over 2,000 bells on it. It forms a flat-topped, dense, dark green mound that is about half a metre high and up to 2 metres across, with every little branchlet terminating in a bright waxy red and white, tulip-shaped bell. It can flower for many months. Unfortunately this form is the one most prone to powdery mildew so be ready. This usually shows up as irregular dark blotches on the leaves. Flowers may be disfigured also.

The bells, first noticed in autumn, colour deepest crimson red on the side that gets most of the autumn and winter sun so choose a position where the north facing side of the plant will be normally viewed. The bells last well, even retaining their tulip shape and bright red and white colour when they dry.

Darwinia meeboldii (Cranbrook Bell)

One of the tallest in the genus, grafted plants of this species are bushy, growing to over two metres on height and over one metre in width, carrying thousands of bells! The bells are flared and tri-coloured green, white and red, hanging at the end of each little branch giving the whole plant the appearance of a decorated Christmas tree. It is a beautiful cut flower with a vase life of at least two weeks.

Darwinia carnea (Mogumber Bell)

The Mogumber bell, is a species on the verge of extinction in the wild . Select the thumbnail image or plant name for a higher resolution image (24k).

This species which has the largest bells of all has almost been wiped out in its natural Western Australia habitat. Because of the density of the foliage of this prostrate plant, make sure that it has good open position with plenty of sun. It is ideal as a basket plant.

Darwinia collina (yellow Mountain Bell)

This is very rare species that occurs only near the summit of several of the highest peaks in the Stirling Range in south Western Australia. It has bright yellow hanging bells that can appear sometimes in autumn as well as in spring. The bells dry well. It needs good air circulation and sun for best development.

Darwinia hybrid (D.macrostegia x D.meeboldii)

This hybrid, which is an F1 cross between the two above species, is a beautiful plant with a combination of characteristics of both of its parent species. It is dome-shaped with light green foliage that is dense to ground level. Bells are large and basically tulip-shaped, bright white in colour with a smudge of bright pink bordering the end of the bell. The pink tonings in the flower develop best in bright sun, so a north facing position is best.

Darwinia oxylepis

Many regard this tallish shrub as the most beautiful of all the Mountain Bells. The brightest of scarlet red flared bells cover the bright green pine-like foliage. This is an excellent cut flower.

From the December 1997 issue of "Australian Plants", journal of the Society for Growing Australian Plants.

Doug McKenzie has been actively growing Australian plants on the Victorian south coast for many years. His experiments into grafting of difficult-to-grow plants has resulted in many of these plants being introduced into general cultivation

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Australian Plants online - June 1998
The Society for Growing Australian Plants