Australian plants have evolved a variety of strategies for reproduction from seed. How they do this and why is important information because it can be used to advantage when propagating natives from seed.
The evolution of seed was a major step in enabling plants to colonise land beyond wetland habitats. Advantages of seed include the protection given from drying out, predators and pathogens to the embryo, and the nutrients they provide for germination.
Seeds are produced as part of the reproductive system of plants. But many Australian genera such as Banksia, produce a small number of seed owing to complex genetic systems associated with in-breeding in small populations.
The seeds of early Australian land plants enabled them to disperse an embryo and food stores into habitats depleted of nutrients and often experiencing extreme temperatures and moisture conditions, for example, seed from the Australian Proteaceae family are often able to survive on maternally derived nutrients for the first year and a half of seedling growth.
Coping with aridity and high temperatures of large areas of Australia presented problems for seed of a number of Australian plants, which also meant adapting complex dormancy release cues such as temperature, heat, nitrate and smoke. When these cues combine with rain there can be a tremendous germination of new plants. The toughest of these will survive to set seed, which then drop and wait until once again the ideal conditions of dormancy release occur.
So to replicate what happens in the wild there are some important tips on to propagate natives from seed.
What types of seed pods do Australian plants produce and how do you collect the seed?
When collecting fruit from plants it is a good idea to only collect from healthy specimens.
There are three basic types of fruit that produce seed:
a.Woody fruits that retain their seed indefinitely:
Many woody natives retain their seed on the plant very conveniently for seed collectors. Plants such as eucalypts, banksias, leptospermum (tea tree), callistemon (bottlebrush) are just a few examples. Simply pick off the woody fruits and put into a paper bag and place on the dashboard of your car where the heat will cause them to open and spit out their seed. Check first to see that the woody capsules have not yet split open and released their seed.
b.Fruits that do not retain their seed indefinitely
There are other plants that shed their seed as soon as it is ripe such as the waratah, wattles and grevilleas. The trick here is to enclose the developing seed pods in a porous material, eg an old panty hose, to catch it as it is shed. Annuals and low growing perennials such as everlasting daisies and Brachyscomes can have a different collection method, whereby you watch for the developing seed heads to become ready to shed their seeds, usually as they change colour to yellow or brownish. Pick off the individual seed heads and spread them out on a flat tray to dry out, after which they will drop the small seeds from the heads (sometimes you need to gently rub the seeds out from the seed heads to get them to drop off). You will end up with an array of plant material, including unpollinated ovaries, chaff and hopefully successfully pollinated and developed seeds. You can pick the seeds which will grow on by their plump and rounded appearance and feel.
Plants such as lilly pillies are designed to be eaten by birds which helps distribute the seed more widely. These should be harvested fresh and can be separated by fermenting the crushed up fruits in a jar or bucket of water. Once the outer seed coat degrades enough you can squish the fruit up allowing the inner seed to be released and collected.
How do you stimulate seed germination?
Many species have mechanisms that prevent the seed germinating all at once in the wild to ensure that seedlings receive the best possible conditions for establishment. Various treatments can be applied to break such dormancies-
a. Hard seed coats (treated with scarification or heat treatment)
Wattles are an example of seeds that have hard coats which are shattered by heat during a bush fire or heatwave. Pouring boiling water over the seeds is the most convenient way of cracking the seed coat at home. Allow the water plus seeds to cool and pour off the water, plant the seeds
Species such as flannel flower are stimulated by chemicals from the smoke of a bushfire. Smoke impregnated water can be used to trigger better germination of such species, and there are also smoke impregnated granules available which work equally well. For more information on smoke treatment and granules, read this article>>>
c. Cold treatment (stratification)
Plants from the alpine areas of Australia such as snow gum need a cold winter to trigger off germination. Putting the seed in the fridge for several months in a moist medium such as coconut fibre will do the trick here.
It also depends on the species as to how to tell if a seed is viable. For larger seeds such as wattles putting seed in water can be revealing with hollow non-viable seed floating to the top and viable seed sinking. Also shrivelled seed is usually not viable so comparing seed (sometimes a microscope is required) will often show a difference between plump viable seed and shrunken non-viable. Also cutting seed open will reveal whether it has a viable food source (starchy white endosperm tissue inside the seed), though this can only be done if you have enough seed to sacrifice the cut one.
How do you care for Australian plant seedlings?
Once the seed has germinated and produced a seedling there are a few tips to ensure it continues growing well.
Use root training pots that are designed to train roots to grow straight down and air prune them. These pots have ribs on the inside and when the roots hit them, they don’t grow around. The best pots have an open structure at the base to give the plant wha is called air pruning.
When transplanting seedlings avoid damage by handling them by the leaves rather than their delicate stems and it is also important to handle the roots with care to avoid damage and develop the best possible long term result especially for trees.
Of course trueness to type of the seedling depends very much on the species in question and also the identity of the parent plants. Generally speaking the native plants we are talking about will show variability between siblings. This can be a good or a bad thing depending on the circumstance. I would emphasise the fact that the genetic variation produced by seed propagation is a very good thing to help preserve biodiversity.
Why propagate Australian plants from seed?
By learning how to extract seeds and what treatment to give them you have the best possible chance of growing Australian native plants for your garden. In particular it’s a good way to grow plants that are indigenous to your area, many of which are unavailable at nurseries.
Be careful about collecting seed pods or fruits as there are regulations about collecting seed in the wild. It is illegal to collect in National Parks without permission. However you can collect seed on private property provided it is not an endangered species.
Keep good records of what you have collected and what you did, so that you can replicate the process in future.
If you want to learn more about propagating plants, you can get my book Let’s Propagate!
And check out my videos on propagating-