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Adding Value To The Business of Cropping

Weed Seed Dispersal Experiment

Learning Intentions:

    Students will be able to:
  • perform simple fair tests on seed dispersal
  • use evidence to support claims about why dandelions are found in so many places
  • describe what a weed is.

Preparation:

  • Find a patch of dandelions with mature seed heads, that can be easily accessed by students. Or, collect 20–40 heads elsewhere and bring them to school for use in the investigations. They don't need to be fully intact.

What You Will Need:

  • Measuring tapes and/or 1m rulers.
  • A battery-powered leaf blower for use on windless days.
  • Optional: tweezers and magnifying glasses.

What to do

On a warm day outside

  1. Explore how dandelion seed parachutes travel away from a mature seed head when you blow on them. Try to see what happens in detail by recording the action using a device's slow motion camera option.


    Make sure plenty of seed parachutes are left over for the next part.
  2. In a still location, take a single seed parachute and gently release it from arm's length in front of you. (You could do this inside if it is windy.) Where does it travel to? Do they fly upwards on their own? Repeat several times to check your results.
  3. IN THE WIND: Release a seed parachute from the same height. Where does it travel to? Measure the distance that it travels sideways before it lands. Repeat several times and work out the average distance. Note: If it's not windy, then use a leaf blower positioned some distance away to create a steady stream of air. Observe if the seed parachutes ever waft upwards and away.
  4. Repeat 3. above, but this time release the seed parachutes from the normal height of a dandelion seed head, say 20 cm above ground level. What distance do they travel on average? Are they sometimes caught by the wind and wafted into the air?

Questions

  1. Describe step-by-step how you think young dandelion plants establish themselves away from the parent plant. What evidence do you have to support your ideas?
  2. What makes dandelions so quick to spread and hard to get rid of in the garden or on the farm? To answer this, research and think about: how many seed heads they produce; how many seeds each head produces and how far they can travel; the period they flower for; how hard the plants are to uproot; how flat the plant is; and, how long the plant can live. 
  3. What is a weed? Is a dandelion always a weed? To answer this find out if it has had, or still has, any uses or value in a garden or as a farm crop.

Going further

Gather your own evidence about another weed's ability to disperse and survive.

Related resources

The science behind dandelion seed parachute flight

Dandelion Clocks Activity

Drawing Dandelion Seeds Activity