Plant Propagation from Seed

Seed of a wide range of Australian plants can be purchased from commercial suppliers and members of the Society for Growing Australian Plants can obtain seed free from the co-operative Seed Banks operated by the various Regional groups.

Not all seed germinates easily. Some seeds have a physical or chemical inhibitor to germination designed so that the seed will only germinate in natural habitats when conditions are favourable. In some cases the inhibitor can be overcome by pre-treatment of the seed before sowing but with others, successful germination has defied all attempts. Beginners are advised to select seed of species which are known to give reliable results. These include Acacia (wattles), Banksia, Callistemon (Bottlebrushes), Allocasuarina (She Oaks), Eucalyptus, Hakea, Hardenbergia and Melaleuca to name just a few.

Pretreatment

For those species where the seed has a natural inhibitor to germination (or dormancy), pre-treatment must be provided before successful germination will occur. There are several pre-treatment methods which can be used:

Boiling Water

This is the most common pre-treatment method and is used with seeds such as Senna, Acacia and all of the 'pea' family in which the hard seed coat forms a physical barrier which is impervious to water.

Boiling water treatment   

These plants are often native to areas where bushfires occur at regular intervals - the heat of the fire cracks the hard coat and allows moisture to reach the embryo inside. Pouring boiling water over the seeds simulates this effect.

The seeds to be treated are placed in a container, covered with boiling water and allowed to stand overnight. Seeds that soften and swell to 1.5-2 times their original size can be sown; those that don't swell are retreated. Any seeds which float are usually infertile and can be discarded. Seed that does not swell after several repeated soaking may need to be treated differently, such as by abrasion - see below.

In some cases seeds will not tolerate excessive time in boiling water and respond better to a one minute immersion in boiling water followed by cooling down. Acacia species native to areas where relatively quick grass fires occur may be in this category.

Abrasion

This can be used as an alternative to boiling water. Seeds are abraded between two sheets of fairly fine sandpaper to reduce the thickness of the seed coat. This can be cumbersome and an alternative is to glue sandpaper to the inside surfaces of a small plastic container, put the seeds in and then shake the container vigorously.

Stratification

A type of dormancy often encountered with seed of species native to alpine or semi-alpine habitats is a requirement for a period of cold conditions prior to germination. This requirement can be accommodated by placing seed in a closed container (containing moist vermiculite or similar material) in a refrigerator for 1-3 months before sowing. This procedure is referred to as"stratification" and examples of seed requiring this treatment are Banksia canei, B.saxicola, Eucalyptus kybeanensis, E.pauciflora, E.regnans and E.delegatensis.

The method has also been applied with some success to non-alpine plants such as Anigzanthos sp. (Kangaroo Paws).

Fire

Apart from the "pea" flowers and acacias, some other seeds seem to require the passage of a bushfire to germinate. Flannel Flowers (Actinotus helianthi), for example, are usually seen at their best in the wild in the seasons immediatley following a bushfire. This effect can be simulated by sowing the seed in a terracotta pot (not plastic for obvious reasons!) and setting fire to leaf litter and twigs placed on top. The fire should be maintained for 2 - 3 minutes. This method has worked but is really a "last resort" method as it is difficult to have any real control over the amount of heat delivered to the seeds. Once the ash has cooled, the pot is watered and maintained as for any other seed raising container.

Smoke

Research in South Africa and Western Australia has shown that smoke is a critical factor for promoting germination of seeds in areas subject to bushfires. The following articles outline some of the general principles involved:

On a large scale, an apparatus like that below can be used to apply smoke to batches of seed. However, this is not particularly practical for the average home propagator.


smoke apparatus
Diagram from Rural Industries Research and Development Corporation Short Report No.48

One practical method of applying smoke treatment is the use of smoked water as a pre-treatment where seed is soaked for 12 hours in a 9:1 water:smoke-water solution. Smoke water can be produced by bubbling smoke through a container of water for about 60 minutes after which the solution is frozen until needed. However, even this is a bit messy. Fortunately, some shortcuts are available:

  • Smoke Water: A product called "Regen 2000 Smokemaster" is available, although it's not the sort of item stocked by your average garden centre and the smallest package is about 10 litres. Further details from the Regen 2000 web site.

  • Smoked Vermiculite: "Regen 2000 Germinator" is a dry granulated smoke-infused product, specifically designed for use on seed trays. Small quantities, sufficient for small-scale use, can be obtained from Nindethana Seed Service. The Wildflower Seed Company (PO Box 804, Canning Bridge, WA 6153) sell "Seed Starter" granules that may be similar to smoked vermiculite (the granules are mixed with hot water and the seeds soaked for for 2-3 hours).

  • Smoked Paper Disks: These apparently originated in South Africa. The seeds are soaked in a container containing one of the disks for 24 hours prior to sowing. These disks are also available from Nindethana Seed Service.

Smoke Responsive Species. In some cases germination has been achieved with species that have proved very difficult or impossible to germinate in the past (eg. Calytrix, Conostylis, Dianella, Eriostemon, Geleznowia, Lechenaultia, Philotheca, Pimelea, Stylidium and Verticordia. For a listing of smoke responsive species, see the Regen 2000 web site.

Leaching

With some seeds there is a chemical inhibitor present which prevents or delays germination. In some cases it is possible to remove the chemical by leaching with various solutions. For example, it has been found that suspending seeds of Eriostemon and some Correa species in a muslin bag in running water for 1-2 weeks improves germination substantially. Unfortunately this is not particularly practical for the home gardener although it has been suggested that leaching could be achieved by suspending the bag in the cistern of a flushing toilet! Other leaching solutions that have been used include alkaline solutions.

The growing medium

A good medium both for seed raising and for subsequent potting-on consists of 80-85% washed river sand and 15 - 20% peat moss. This mix has been used successfully by many growers over a long period although, given the environmental problems associated with peat extraction, an artificial peat moss would most likely be substituted by many propagators. There are a number of these "artificial" peats available made from waste products such as coconut fibre.

Of course, commercial seed raising mixes can also be used. The medium should be reasonably moist before sowing the seed.

Planting the seed

Seed can be sown into punnets, small pots or tubes and is normally covered to a depth of about double the seed diameter. Fine seed is usually sprinkled over the surface of the seed mix and need only be pressed down firmly onto the mix without being actually covered. Large seed needs to be well spaced to facilitate later transplanting. The use of individual tubes is an advantage when only small quantities of plants are required. This allows large seed to be sown one to a tube while fine seed can be thinned out as germination occurs to leave the strongest single seedling.

Care and attention

After sowing, the seed bed needs to be kept moist and sheltered from drying winds and from rain. Some sunlight is an advantage.

Capillary Bed Diagram   

With overhead watering, a fine spray is necessary to avoid damage to small seedlings. A good method of watering for small quantities of seed is the use of a capillary bed (as shown in the diagram). With this arrangement, overhead watering is not needed and the seed and seedlings can be left unattended for 2 or 3 days (up to a week or more in cooler weather). The seed mix in the containers needs to be fairly moist before the containers are placed in the capillary bed otherwise the capillary action may not occur.

A similar method is the so-called "bog method" where the pot containing the seed is placed into a saucer of water until germination occurs.

Pests and diseases

'Damping-off' causes rotting of the stems of seedlings at soil level, particularly in seed mixes that are over-wet. The problem can be difficult to control without the use of a fungicide. The use of sterilized seed raising mixes and sowing so that seedlings are not crowded are the most effective ways of preventing infection.

Snails and slugs can cause rapid destruction of small seedlings. If these can't be controlled by physically removing them, the usual baits should give protection. Any caterpillars that appear are best removed by hand...the use of chemical sprays is hardly justified for this situation.

Pre-germination

This is a useful technique for large seeds (ie those which can be handled easily individually). It involves sowing seed into a sealed contained containing a layer of moist vermiculite or even a moist paper towel. Any required pre-treatment needs to be carried out as normal before sowing. The container is then placed in a cool, dark place and checked every week or so until germination commences. Any seeds which have germinated are carefully removed and potted into small pots or tubes as described below. The remaining seeds are re-sealed in the container which now needs to be checked every 1 - 2 days as germination of the remaining seeds usually occurs quickly once germination has commenced.


Pre-germination Diagram

Using this method, seed can be sown during the colder months when outdoor temperatures may be too cold for effective germination.

Transplanting

Seedlings growing in punnets or the like can be potted into individual tubes (or small pots) when they are large enough to be handled. This is usually when the second pair of leaves appears. Individual seedlings are carefully removed from the seed bed using a knife or narrow spatula (eg. a piece of aluminium about 100 mm long by 10 mm wide is suitable). Each seedling should be placed into a partly filled tube and potting mix gently firmed around it preferably using a gentle water spray from a hand-operated spray bottle. A small amount of slow release fertilizer in the potting mix is an advantage at this stage.

Growing-on

After transplanting, the seedlings need to be placed in a protected position for a couple of weeks and gradually moved into a situation where full sun is available for at least part of the day. The seedlings must not be allowed to dry out and the tubes containing the seedlings could be placed in a capillary bed to minimize this possibility. After 1-3 months tubed seedlings will be ready to transplant into larger (125 - 150 mm) pots.

Planting out

Plants will be ready for the garden when good root development has occurred. This can be checked by carefully tapping the plant out of the pot. The roots of the plants should not be allowed to become "pot-bound" (ie. develop into a tight, coiled mass). If this does occur, some root pruning will be needed before planting to ensure that the roots of the plants can easily spread into the surrounding soil.


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