Jarrah Bark Environment

Smoke chemical triggers wildflower germination

Environmental editor

• The great mystery of how wildflower seeds know when space and nutrients are available for successful germination has finally been solved. Research in Western Australia and South Africa has discovered that the answer has been butenolide (b-you-ten-oh-lied) a chemical present in wood ash and smoke which sends a critical signal to the seeds.
  
  Australian wild flowers particularly have only managed to survive for countless hundreds of thousands of years because they have learned to germinate at the right time and in the right place.
  
  If germination occurs immediately prior to hot and dry conditions or in areas that are already well populated by other plants the chances of the seeds becoming a shrub or tree are extremely remote. A great number of species therefore react to two basic triggers.
  
  Firstly the seeds must become "aware" that competing plants have been considerably reduced and that nutrients are available for healthy growth. This has usually been caused by a bush fire during the previous summer and autumn.
  
  The fire has also cleared the ground of toxic leaf mulch and covered the ground with nutrient rich ash which is absorbed into the top soil. Butenolide is manufactured in the fire as it burns the plant material.
  
  The next trigger is a rising soil temperature as is the case in the spring. The soil is moist and winter rains have infused the essential plant nutrients and butenolide into the top few millimeters of soil. The seed must germinate at this time to allow it to become well established with feeder roots before the inevitable summer drought appears.
  
  The seeds therefore absorb nutrient rich moisture and germinate in response to chemical signals and rising temperatures. Butenolide is now available from some garden nurseries in packets sufficient for two standard seed trays. More information from

  CREATING THE RIGHT CONDITIONS

  Sending the correct temperature signals to the seeds is straight forward. Simply keep the seeds in the bottom of the refrigerator in moisture proof containers for at least six weeks. Removing the seeds from the refrigerator will trigger the seeds temperature sensors.
  
  Probably the best and easiest way to duplicate natural germinating conditions is with seed trays filled with expanded clay. Expanded clay is usually available from hydroponic retailers. Purchase the smallest grading. Sieve off the dry dust and keep this to one side.
  
  Also have available a larger tank or saucer big enough to allow the seed tray to be placed in the tank. This will be filled with the seed germinating mixture to allow the seed tray to be flooded. A flood and drain tank is by far the best way of watering and feeding any young seedlings.
  
  Next spread a thin layer of expanded clay dust over the top of the tray. This fills the cracks between the clay pellets and prevents fine seed from falling too deep into the bed. Seed directly onto this thin layer of dust.
  
  Very fine seed such as Kangaroo Paw can be mixed with a small amount of dust and then placed in a pepper shaker for spreading. Tweezers can be very useful for placing Banksia and pea type seeds on top of the bed. Use more dust to cover the seed to twice the diameter of the seed.
  
  Flood and soak the trays overnight in rain or distilled water (don't trust tap or bore water) to which butenolide and a complete wildflower nutrient mix have been added. Next carefully lift the tray out of the flood tank and allow it to drain back into the tank.
  
  Many seeds can benefit from an overnight soaking in hot (not boiling) water. Large seed may be left uncovered overnight. Viable seed will swell and seed that has not swelled can be removed. Germinating the seed during the cooler months may require the use of some form of bottom heating to keep the tray temperature at between 20° and 30° Celsius.
  
  Raising the temperature by growing under glass or in mini-glass houses can also be successful but the air temperature is not as important as the root zone temperature.
  
  Butenolide is now available to the home grower from a number of garden nurseries. One excellent product sold by is vermiculite which has been impregnated with butenolide.
  
  

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