A weed is simply a plant that is growing where it is not wanted. But why are they considered such pests? Here are some things you didn't know about weeds.

Wily weeds
There are many ways in which they succeed in popping up in the most inconvenient of places:
by growing very fast, often smothering other plants to get the most light, minerals and water
by producing lots of seeds and having lots of different ways of spreading them around
by germinating their seeds quickly
by producing seeds that survive over several years
by having effective defence systems that protect them from being eaten by animals or picked by people, for example, stinging nettles
by multiplying in more ways than one, usually making new plants along their stems

Interesting facts
Stinging nettles are often used in herbal medicine for cleaning the body and making the heart work better. Nettles are packed full of vitamin C and new shoots are often used to make tea.
There are many superstitions linked to weeds. For example, if you hold a buttercup under your chin and a yellow shadow appears, it means you like butter. Or, finding a four-leaf clover brings good luck. And if you touch a dandelion you will wet the bed! The French word for dandelion is Pissenlit, which directly translated means 'wee in bed'. Weeds such as wild carrot, cow parsley and celery grow at least 350 seeds on a single flower-head. Wild clematis grows climbing, sprawling stems up to 30m long (100ft) - that's about 20 people from top to toe!

Step-by-step guide
1 First your children should place some crocks at the base of their plant pot.
2 Then they need to half-fill the pot with soil or compost.
3 Help them to dig up a dandelion. They must get most of the long taproot up with it, without which it will quickly die. (The taproot is the straight, tapering root growing vertically downwards and forming the centre from which subsidiary rootlets emerge.)
4 Help your children to plant it in the pot, and firm it in with more soil or compost.
5 Let them water it well, then put it on a windowsill.
6 Look at it regularly. They should see it grow buds, then the flowers will open, then they'll die, and finally the seed clocks will form.
7 Their dandelion should grow quite a few flowers. They can count how many it grows, then see if they can guess how many seeds it has produced - hundreds!

Useful information
Many plants are known as weeds because they are successful at growing where more delicate species would die. Dandelions are strong plants. In fact, the trauma of being dug up will actually stress the plant and cause it to produce more flowers, rather than killing it. Eventually it's likely to die in the pot.

The function of all flowering plants is to produce seeds. Once the seeds have grown and ripened, the plant has to get them to somewhere that they will be happy growing.

Plants have many ways of spreading or dispersing their seeds.
gravity - heavy seeds will just fall off the plant.
wind - very fine seeds will blow away on the wind. Some seeds have special parachutes or wings to help them fly, for example, dandelions.
hooks - the seeds are covered with hooks which catch on to a passing animals' fur; they then catch a free ride to another place where they are rubbed off later.
animals - the seeds look like tasty treats for the animals to eat, but they pass undigested through the animal. Animals, including birds and insects, sometimes bury the seeds.
pepperpot - the seed-pod is like a little pepperpot and sprinkles the seeds over quite a wide area.
exploding - the seed-pod bursts suddenly, throwing all the seeds out over a large area.
floating - some seeds grow with air trapped in them, so they can float away from the parent plant.

Your children might know what is inside an apple or an orange - but what about some of those exotic fruits at the shops? This exercise will reinforce the fact that a fruit is a plant's way of dispersing its seed. And it should stimulate their imagination.

What you will need
some exotic fruit from the market or supermarket. Look for ones they have never seen before.
an adult
a sharp knife
a pencil and felt pens
paper folded into four quarters
Step-by-step guide
1 Ask children to choose one of the fruits and write its name down in the first box on the paper if they know it.
2 Next they should draw a picture of it in the second box. Tell them to look carefully at it. Has it got a pattern? Does it have hairs or prickles? What colour is it?
3 In the third box, they can draw what they think it looks like inside. What colour is the flesh? What about the seeds - are there lots, or is there just one pip or a big, hard stone?
4 Cut it carefully in half for your children. Did their drawing look similar to the inside of the fruit?
5 Ask them to draw it in the fourth box. Again, they need to look carefully, so that their picture shows what is really there.
6 Try it again with different fruits.