The Mint Bush Family - Propagation

Introduction

Members of the mint bush family are usually grown from cuttings as many of the most horticulturally desirable species strike readily.

Seed

The ease of propagation from seed varies considerably between the different genera within the family. In some cases germination occurs readily (eg. Ajuga, Plectanthus) but in other cases can be unreliable (eg. Prostanthera, Westringia, Hemiandra) and fresh seed usually gives the best results in these cases.

Pretreatment of seed prior to sowing to improve germination is not normally beneficial with members of this family. However, a 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 Hemigena and may have practical application for the home propagator for this and other genera in the Lamiaceae. 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

Most shrubby members of the Lamiaceae strike readily from cuttings using hardened, current season's growth. Cuttings about 75-100 mm in length with the leaves carefully removed from the lower two-thirds seem to be satisfactory. Treating the lower centimetre with a "root promoting" hormone both seems to improve the success rate but is often unnecessary.

Members of this family serve as a good introduction to those starting out in propagation from cuttings as success rates are usually high.

Division

Some members of the family (eg. Mentha) produce suckers from their root systems. These can be cut from the parent plant (ideally retaining some of the roots) and potted into individual containers. If placed in a sheltered location and kept moist, these should develop quickly into new plants.

Grafting

Considerable work has been carried out on grafting with Prostanthera to improve the hardiness of the genus in areas where they are difficult to grow.

Most species of Prostanthera are compatible with a root stock of Westringia fruticosa, a very reliable plant suited to many districts. Grafting of Prostanthera species to W.fruticosa is not difficult and, like cuttings, is a good project for those starting out in grafting. A number of other westringias (eg. the cultivar "Wynyabbie Gem") have also been successfully used as root stocks for Prostanthera species.

There are some prostantheras which are not compatible with W.fruticosa. These include P.aspalathoides and P.calycina. These can be grafted using the "nurse graft" technique which is explained (along with basic grafting methods) in the article Grafting Prostantheras

Little or no work has been done on grafting of other genera of the Lamiaceae. There is plentty of scope for experimentation for the keen amateur, particularly in improving the hardiness of species in the genus Hemiandra (eg. H.gardneri, H.pungens).

General Propagation

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


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