The Boronia Family - Propagation

Introduction

Propagation of the Boronia group of plants from seed is usually difficult and propagation by cuttings is the preferred method. This also enables plants with desirable characteristics of form or flower colour to be perpetuated. Some work has been carried out on propagation by grafting.

An excellent review of propagation methods for Boronia can be found in the article Propagating Boronia. The methods can usually be applied to related genera.

Seed

A frustrating feature of the Boronia group of plants for home propagators who try without success to germinate seed, is that seedlings will often come up in freshly graded road verges near natural bushland and even in gardens!

Seed of the group has a hard (usually black) seed coat and appears to have an inhibitor to germination designed to ensure that germination only occurs in nature under favourable conditions. Some research has been carried out into ways of overcoming this dormancy with a degree of success being achieved. For example, it was found some years ago that placing seed of Eriostemon australasius in a muslin bag in running water for up to 2 weeks seemed to leach out the inhibitory agent, allowing germination to proceed. It is possible that such a method would be successful with other members of the Boronia group but it is of limited practical use to most home gardeners although it has been suggested that leaching could be achieved by suspending the bag in the cistern of a flushing toilet....so far no one has admitted trying this!.

Another method that has been successful for at least some species is the use of smoke or "smoked water" as a pretreatment. This has been successful in the germination of species of Geleznowia and Philotheca and may have practical application for the home propagator. Further information on this procedure is available in the article Smoke Stimulates the Germination of Many Western Australian Plants (see Further Information) and from the Regen 2000 web site.

Cuttings

Many plants in the Boronia family are readily propagated by cuttings using hardened, current-season's growth. Cuttings about 75-100 mm in length, taken in January in southern Australia would normally be suitable with the leaves carefully removed from the lower two-thirds. "Wounding" the lower stem by removing a sliver of bark and treating with a "root promoting" hormone both seem to improve the success rate.

Grafting

Some research has been carried out on the grafting of members of the Boronia family, mainly by enthusiastic amateurs. Because of the difficulty of growing some desirable members of the family on their own roots, grafting onto hardy rootstocks offers the potential to expand the range where those plants can be successfully cultivated. Grafting is quite common with some exotic members of the family (eg grafted orange, lemon and lime varieties) and some success has been achieved with native species. However, as far as is known, little commercial grafting of native species is being carried out at present.

There are two factors to be considered when selecting suitable rootstocks:

  • Hardiness of the stock - the selected stock needs to be reliable in the area where the grafted plant is to be grown.
  • Compatibility between stock and scion - the closer the relationship between the stock and scion, the better the chance of success. Stock and scion of the same species is ideal, stock and scion in the same genus is often successful and stock and scion in closely related genera may also be suitable if other options are not viable.

Those wishing to undertake grafting experiments might consider some of the following rootstock suggestions, but available data on compatibility is scarce and anyone working with these plants are encouraged to document their results, both successful and otherwise.


Table 3 - Possible Scion / Rootstock Combinations

Species Possible Stock
Boronia sp. Boronia denticulata, B.clavata, Zieria smithii
Correa sp. Correa alba, C.glabra, C.lawrenceana
Phebalium sp. Phebalium squamulosum, Philotheca myoporoides (syn. Eriostemon myoporoides)
Eriostemon sp. Philotheca myoporoides
Crowea sp. Philotheca myoporoides

General Propagation

Further details on general plant propagation can be found at the Society's Plant Propagation Pages.


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