Successful germination of wild plant species is often problematic. It is hoped that by providing access to the Tasmanian Seed Conservation Centre’s (TSCC) Germination Database we can provide some guidance as to what approaches will work best. Germination data can be sought from the database taxonomically, via the plant family or genus.

Cuscuta tasmanica seedling
Cuscuta tasmanica (Convolvulaceae) seedling. Techniques successful in the lab can be adapted for home trials.

At the TSCC, seed germination requirements are investigated in laboratory conditions. However with a little effort the information in the Germination Database can be interpreted for germinating native seeds at home.

Please do not be put off by seemingly complex methods! It is relatively easy to germinate seeds of many native plant species at home, even those that possess dormancy, with no specialist equipment and little experience.

Germination test reports

Each report in the Germination Database contains the following information about the seed collection and its germination requirements. Those in bold will be of most interest to you:

  • Genus and species
  • Time and place seeds were harvested
  • A TSCC accession number for banking purposes
  • The date germination testing began
  • Germination test result (total percentage of viable seed germinated)
  • Germination rate (number of days it took for half of the final germination result to be acheived)
  • Test conditions
  • Who carried out the test

In addition, all reports include further explanation on the last page.

The most important things to note are:

1. The test conditions:
For each report, the test conditions marked ‘recommended’ are those which the TSCC use to re-test the collection approximately every 10 years to monitor collection viability. These are also the germination conditions recommended to those requesting seeds from a TSCC collection. Although the ‘recommended’ test will generally yield the highest germination in minimum time, this is not always the case and looking at the response of seeds to the range of tests carried out will often be very revealing (see examples below).
2. The test results:
Percentage germination results, along with germination rate, are used by the TSCC to flag optimal germination conditions across the range of tests.

Germination medium

You will notice that the TSCC sow seeds onto 1% agar. This is simply an opaque medium that keeps the seeds moist and allows initial germination to be visible. For the purposes of home growing, we recommend sowing seeds in pots or trays of a good commercially available seed raising mix. Such mixes are as good, if not better in many cases, as the agar media the TSCC use. Keep the seed mix moist, but not water-logged.

Germination temperature

The most important thing to note is the germination temperature (°C). This will give a general indication as to what time of the year to sow your seeds.

For example, consider the following germination test results, including germination rate, for Diplarrhena moraea (Iridaceae);

Diplarrhena moraea - germination test results, including germination rate

Diplarrhena moraea – germination test results, including germination rate

Diplarrhena moraea will clearly germinate over a wide range of temperatures but prefers lower temperatures. For rapid germination, seed should be sown outdoors in autumn, expected to germinate in winter and seedlings will be well established by the spring.

These results contrast with the germination behaviour displayed by lowland, understorey species belonging to the Pomaderris genus (Rhamnaceae). Germination of these species declines and stops above 20°C, showing definite restriction of germination to the cooler months of the year. Indeed Pomaderris species tend to grow in drier conditions compared to Diplarrhena species and seeds will therefore avoid germination if there is a chance of the surface soil drying out.

Compare the Pomaderris germination strategy with germination results for Eucalyptus brookeriana (Myrtaceae);

Eucalyptus brookeriana - germination test results, including germination rate

Eucalyptus brookeriana – germination test results, including germination rate

In the laboratory, germination of E. brookeriana was rapid across a very broad range of temperatures, indicating that in the field, germination will take place at any time of the year providing the soil is wet.

N.B. Do not worry if you are unable to recreate the constant temperature regimes used by the TSCC. Seeds will probably respond as well, if not better, to natural alternating temperatures. Results generated by the TSCC should be used merely as a guide to the best time of year to sow seeds for germination.

Germination photoperiod

You will notice that the TSCC uses a 10/14 hour photoperiod. This means that for 10 hours each day seeds are exposed to light and for the remaining 14 hours they are in darkness. This simply reflects the natural photoperiod reminiscent of spring and autumn in Tasmania, which is when the majority of Tasmanian seeds are expected to be germinating in the wild.

However, photoperiod is only relevant if seeds are on the soil surface and light is generally only important for the germination of small seeds (less than 4 or 5 mm in length).

At home, seeds greater than 5 mm in length can be sown under the soil surface and photoperiod ignored. Seeds less than 5 mm should be sown on or close to the soil surface and natural day / night photoperiods will be perfectly adequate for germination. A good technique is to surface sow small seeds and then lightly dress the pot with a sprinkling of small, but not fine, grit. This allows light to reach the seeds but prevents the seeds from being disturbed too much by watering and helps create a humid atmosphere at the soil surface.

If you suspect that seeds greater than 5 mm in size require light for germination, sow seeds both on and under the soil surface and note germination patterns.

Overcoming seed dormancy and stimulating germination

Does the germination report suggest that your seeds require treatment prior to sowing for germination, or additional germination stimulants once sown? If so, your seeds may exhibit dormancy.

Prior to sowing seeds:

A period of dry storage or dry after-ripening

A period of dry after-ripening may alleviate physiological dormancy. To achieve dry after-ripening at home, you may want to seal seeds inside a paper bag and store them in a warm (not hot), dry place for a number of weeks, for example, a north facing windowsill during summer, inside a boiler cupboard, close to a storage heater or on a veranda. Overcoming physiological dormancy can also be achieved.

Removal of seed covering structures

Removal of seed covering structures may alleviate physiological or physical dormancy. The TSCC advises that wherever possible, seeds are sown without covering structures such as husks and fruits.

N.B. It is vital that wet fruit and pulp is removed from around seeds soon after collection to prevent seed decay and reduced seed viability. Read more about the importance of drying seeds here.

Washing and soaking

Washing or soaking seeds may alleviate chemical dormancy. It may be necessary to soak seeds in water or detergent for some hours prior to sowing. Such pre-treatments may act to wash away germination inhibitors, and/or prevent significant mould developing around seeds.

Seed coat removal or chipping (scarification)

Seeds exhibiting physical dormancy will require scarification of the seed coat simply to allow seeds to absorb water. If possible, make a small incision into the coat of each seed using a scalpel, preferable away from the seed embryo. If the seed coat is too thick for this approach you might consider using a vice to crack the seed coat. Alternatively files used to sharpen saw teeth or a hand-operated drill can be used to penetrate the seed coat whilst the seed is securely fixed in a vice.

For examples of chipping seeds at the TSCC, see Germination Reports for Fabaceae species.

One common technique in tackling physical dormancy is to place dry seeds into a glass of just boiled water and leave it to cool. The heat causes the seed coat to crack and permits the intake of water.

Heat Shocking

Applying high temperatures for short durations has a similar affect upon seeds as scarification, but may also encourage germination of species that are not physically dormant. At the TSCC, a tray of sand or fine grit is pre-heated to 90 to 100°C in a conventional oven before a small paper or foil envelope of seeds is pushed into the sand. The tray is then placed back into the oven for about ten minutes. Remove the packet from the tray and allow to cool. Once cooled the seeds can then be sown.

Once seeds are sown:

Potassium nitrate

You will notice that many seeds have been found by the TSCC to respond to application of potassium nitrate (KNO3). However, along with many other minerals and nutrients useful to seeds/plants, KNO3will be present at adequate concentrations in commonly used seed raising mix therefore nothing additional is necessary.

Smoke solutions

Smoke is reportedly an effective chemical agent for terminating dormancy / triggering germination in a wide variety of Australian native seeds1. For example, dormancy of Schoenia filifolia subsp. subulifolia (Asteraceae) was overcome by smoke-water, eliminating the requirement of light for germination2. The active component of plant- and cellulose- derived smoke has been identified as ‘karrikinolide’ (3-methyl-2H-furo[2,3-c]pyran-2-one)3 , but exactly how karrikinolide promotes seed germination is still unknown.

So far only one collection at the TSCC has exhibited a significant response to smoke (Ozothamnus lycopodioides, Asteraceae), and upon re-testing this is now in question.

For home use, smoke solution can be purchased in two forms:

  1. 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.Mr Fothergill’s Seed Australia sell Seed Starter Granules for wildflowers, which may be similar to smoked vermiculite.
  2. Smoked Paper Disks: 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.

For some species, application of smoke solution after one or two seasons might yield better results. The concentration of smoke solution used should also be considered as high dosages can be toxic or at least inhibitory.

References:

  1. Merritt DJ and Dixon KW. 2003. Seed storage characteristics and dormancy of Australian Indigenous plant species: From the seed store to the field. In: Seed conservation: Turning Science into Practice. RD Smith, JB Dickie, SH Linington, HW Pritchard and RJ Probert, eds. Royal Botanic Gardens Kew, 807-823.
  2. Plummer JA, Rogers AD, Turner DW and Bell DT. 2001. Light, nitrogenous compounds, smoke and GA3 break dormancy and enhance germination in the Australian everlasting daisy, Shoenia filifolia subsp. subulifoliaSeed Science and Technology 29: 321-330.
  3. Flematti GR, Ghisalberti EL, Dixon KW and Trengove RD. 2004. A compound from smoke that promotes seed germination. Science305: 977.