Horticulture - Grafting

Grafting is another means of vegetative propagation. Plant material is grafted onto a rootstock which is more vigorous, long-lived, resistant to pests and disease, or better suited to the local conditions. For instance, in recent years Prostanthera grown in the Gardens were grafted to the hardy rootstock of Westringia fruticosa. This plant is thought to be less susceptible to the Phytophthora cinnamomi or Cinnamon fungus disease.

Nearly all of the Eremophila plants in the Gardens are grafted onto Myoporum insulare. Eremophila are prone to fungal diseases, especially Botrytis cinerea in the propagation nursery. Most Eremophilas grow in sandy, well-drained soils which are very different to the heavy clays of the Gardens. They are hard to establish unless grafted onto a suitable rootstock. M. insulare appears to be tolerant of a wide range of soil types and demonstrates some disease resistance.

Horticulturists in the nursery generally use top wedge cutting grafts for grafting Eremophilas. The method is to:

Select a piece of stock material (scion) approximately 100 mm long and remove the lower leaves.
At the top of the rootstock, make a cut approximately 5 – 10 mm long.
The cutting to be grafted (scion) should be 60 – 80 mm long with the same number of leaves as a standard cutting.
The lower portion of the scion is cut into a wedge shape 5 – 10 mm long and inserted into the cut in the stock stem.
The join is wrapped in a stretchable tape such as florists tape.
The stem of the rootstock is cut and dipped in rooting hormone.

Anecdotally, the grafted plants seem to survive longer than the same plants on their own roots. Whether this is valid scientifically needs further investigation and reporting.

Another reason for grafting at the Gardens is to propagate and conserve threatened species.