Kid Questions – How Do Plants Grow, and Why Do Weeds Grow?

by Deb on March 12, 2010

Plants are actually very similar to animals – they do a lot of the same things but stay still, and they need a lot of the same things like water, nutrients and energy.  They just get them in slightly different ways.

Plants get their energy from the sun, they collect it through their leaves.  They get their nutrients like vitamins and minerals from the ground through their roots.  They get water through their roots too.

A seed is a bit like an egg.  Inside it has a baby plant, and the rest of the seed is food to keep it going until it can get food for itself.  This is why we eat so many seeds – they’re good food for us too!

Here you can see the baby plant inside the seed.

When the baby plant is warm and moist it starts to break out of the seed.  It grows two shoots, one goes down and becomes the roots the other grows up and sprouts leaves.  These first leaves are important because they need to start getting energy for the plant to keep growing.  Then the plant grows like we do – as it gets more energy, food and water, it uses them to make new cells.  The vascular plants, which are most of the ones we know, even have special parts called phloem (fleem) and xylem (zy-lem) that carry nutrients and water around the plant a bit like our blood.  This is the sap you see when you break a plant stem.  They react to being cut or broken by producing hormones a bit like our pain chemicals.

Weeds

Weeds are just plants growing where they aren’t wanted, so they could be fine in one place but a weed somewhere else.  This is a problem in Australia because so many garden plants are introduced and then get loose in the bush, blackberry is a good example.  But most of the things we call weeds have some things in common –

  • They grow quickly and easily, not needing a lot of nutrients.
  • They produce lots of seeds very quickly.
  • The seeds tend to be very ‘sticky’ or spread a long way very easily.  Ruby dock has spread around a lot of central Australia because it dries to be soft and fluffy and blows around in the wind.
  • A lot of them are prickly or poisonous.

What this means is that a young weed can start growing anywhere because they don’t need much, they get big quickly and use up all the nutrients other plants could use.  Plus when they get big they can shade other plants so they don’t get as much sunlight.  The prickles or poison protects them from animals, then they make lots of seeds that spread a long way and start all over again.

It’s very important to protect our native vegetation from introduced weeds, it’s needed by native wildlife and makes our unique ecosystems.  If you have native plants in your garden they’re much easier to care for because they are adapted to the local weather and soil, and you are likely to get far more native birds and reptiles visiting.

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