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Grafted Hakea

Doug McKenzie

Over the past twenty years, grafted Hakea have been produced commercially and successfully grown in a variety of soils in gardens in eastern states; even in Adelaide or northern Victoria, in home gardens that are frequently watered or fertilized more than would usually be tolerated by these dry country species. Grafting Hakea, like any plant, is usually done to increase tolerance and enable strong growth in a wider range of conditions. Sensitive species are grafted onto tougher root-stock species with a recognised tolerance.

Grafted Hakea are suitable for planting in private and public gardens. Mass plantings in public open space, on nature strips, roadside or freeway plantations or golf courses make the most of their spectacular flowers and their tolerance of a range of site conditions.

Of the 130 species of Hakea half, probably with the greatest diversity, are found in the south-west of Western Australia. Many are highly ornamental with dramatic flowers and interesting fruit and some species have particularly striking foliage. In Western Australia soil types include deep sand to granite or gravelly Iaterite and red loams and grafting will accommodate these plants on eastern soils.

To determine the compatibility of species for grafting, a series of trials were undertaken at Bushgrafts Nursery in Ocean Grove, Victoria. Most grafts were completed using seedlings (both stock and scion) selected at cotyledon leaf stage. This method of grafting reduces the problem of stock shooting. The graft union, on now mature 13 to 14 year-old plants, is excellent, usually detectable only as a change in the bark texture between the stock and scion species. An ugly knot does not occur at the graft union as it may in other methods. The disadvantage of cotyledon seedlings grafting is that particular forms cannot be reliably replicated because seedlings are used as both stock and scion.

Two of the most spectacular of the western hakeas Hakea bucculenta (left) Hakea multilineata (right) Click for a larger image

There is, however, no evidence that compatibility varies when different provenances of either stock or scion are used: if two species are compatible, seedlings from seed taken from any source will unite and grow well. Another minor disadvantage in this technique arises from the fact that young seedlings are also used as stock plants. Therefore, the graft is relatively close to the ground and care needs to be taken when planting out or potting on that the young plant is kept as high as possible from the soil surface to allow for greater air movement between the seedling and the soil surface. This problem can be reduced by using seedlings, deliberately produced by selection, that have long hypocotyls.

To date, no problem with scion rooting has been noted. It is recommended that grafts produced using this method are planted in the centre of a slight mound when they are finally planted out.

Grafting Trials - Results

Scions used: Hakea bucculenta, H.'Burrendong Beauty', H.cucullata, H.francisiana (and its form H.coriacea), H.grammatophylla, H.laurina, H.lehmanniana, H.minyma, H.multilineata, H.myrtoides, H.lorea (formerly H.suberea) and H.victoria.

Stock plants: Hakea laurina, H.nodosa, H.salicifolia, H.drupacea.

While grafted plants flower profusely when planted in the ground they are unfortunately shy to flower in pots, unless they are grown in very large containers for quite a few years. In southern Victoria, flowers are generally produced in one to two years after planting out for Hakea multilineata and two to three years after planting out for most other species. Hakea bucculenta seems to be the slowest to flower, often taking four or more years. These flowering times may be much shorter in warmer climates.

Hakea victoria Click for a larger image

At the Australian National Botanic Gardens, Canberra, a number of grafted Hakea (most on H.salicifolia root stock) are growing very well ranging in age from 12 to 22 years, all grafted at the cotyledon stage.

Phytopthora resistant? Grafted plants growing at the Australian National Botanic Gardens, Canberra, are close to an area where Phytopthora cinnamomi was first isolated in the gardens. Very few plants susceptible to this fungal disease have survived in the bed. Hakea salicifolia is often quoted as being resistant to the cinnamon fungus, so it is not surprising that grafted plants have survived in these conditions.

A leaf spot disease is an occasional problem in very humid conditions. It can disfigure and set back a young plant. Juvenile foliage on very young plants in pots may be affected in autumn or spring, but this problem is not likely to worry plants in the open garden. The leaf spot disease has been identified as bacterial. Kocide, or another copper spray is effective in preventing infection but it should be applied to the unopened leaf buds as a preventive measure. It will not cure leaves on which the spot has appeared. These should be cut off when first noticed and the whole plant sprayed, especially the unopened leaf buds.

Ornamental Trial Notes

Hakea bucculenta: This takes a few years to flower in cool climates, but the wait is worthwhile. Some descriptions of this species indicate that it often produces bright red flower spikes hidden within the foliage. On fairly large, bushy, grafted plants in full sun, flowers have been produced in masses across the top of the foliage giving the appearance that the plant is on fire.

Hakea cucullata: Only two specimens of this species were grafted onto H.salicifolia to test compatibility. These plants are growing well, but as it is fairly hardy in most climates, it may be unnecessary to graft this plant.

Hakea francisiana: A species which forms a dense, bushy, small tree and also grows rapidly in good conditions. Three to four-year-old plants come into flower when they are approximately 2 m in height. Hakea salicifolia appears to be the most successful stock for this and other 'grass-leafed' hakeas. Plants using H.nodosa as stock are slower and seem to have a tendency to become loose in the pot. However their root system develops and they soon strengthen when planted out. H.francisiana fails completely with H.drupacea stock and does not grow very well on H.sericea.

The form of H.francisiana previously known as Hakea coriacea: This performs well as a grafted specimen. It is the tallest of the group of plants trialled. It was not compatible on H.laurina and has not been tried on H.sericea.

Hakea grammatophylla: This species is from central Australia and is growing well as a grafted plant. When planted in an open sunny position, it produces masses of beautiful deep-pink flower spikes, even during the dreary, moist, cold winters on the southern coast of Victoria. The smallest of the 'grass-leafed' group, it becomes a rounded shrub of up to 2 m in approximately 10 years.

Hakea lehmanniana: A small number of this species have been trialled on H.salicifolia and they appear compatible.

	Hakea 'Burrendong Beauty' (top) Hakea myrtoides (bottom) Click for a larger image

Hakea 'Burrendong Beauty': This is a natural hybrid, that originated at Burrendong Arboretum in New South Wales. It is a small spreading species often grown on its own roots which are quite vigorous and hardy. This species grafted onto H.salicifolia indicates no compatibility problem.

Hakea laurina: This species is in wide demand but it is often difficult to grow on it own roots. In southern Victoria it is reliable as a stock species, however it unfortunately seems incompatible as a stock for the 'grass-leafed' species. When using as a scion and grafted onto H.salicifolia, it falls off the stock after initial fast growth.

Hakea minyma: A a central Australian species that is very vigorous when planted in a warm position. It has been growing for quite a few years grafted onto H.salicifolia and has been flowered in Victoria. It is not so spectacular as the other 'grass-leafed' species.

Hakea multilineata: This is the fastest growing scion species, the distinctive beautiful axillary flowers forming 'spikes' up each branch. It is the earliest flowerer of the group, flowering at two or three years from seed when grafted onto H.salicifolia stock. Hakea nodosa stock is satisfactory, although slower. The rate of growth on H.sericea stock was slightly slower and the foliage yellowed for a few months after grafting. H.multilineata is not successful on H.laurina or H.drupacea.

Hakea myrtoides: Grafted plants at about four years old grow more vigorously than plants growing on their own roots. Grafted plants send out numerous side stems from a central lignotuber-like structure to form round, mounding shrubs up to 1 m in diameter. However, after about 4 to 5 years, the plants seem to deteriorate due to dieback of foliage and grafting is not very successful in overcoming this insect problem.

Hakea lorea (syn. H.suberea): A number of grafts on H.salicifolia have been made and the plants have grown very slowly to 50 cm after 11 years. These plants will not thrive in cold conditions even as grafted plants.

Hakea victoria: Six grafted plants were produced on H.salicifolia stock. They grew normally for six to eight months then all broke off cleanly right at the graft, indicating that the scion and stock were incompatible.

From Australian Plants, journal of the Association of Societies for Growing Australian Plants, December 2000.

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Australian Plants online - June 2002
Association of Societies for Growing Australian Plants