Because people want to grow stuff that won't survive otherwise.

nr,

In addition to jean's comments, they want an Oasis in the desert. Not desert scrub flowering only after the April showers. JMHO Aloha

NickRose, I begin to learn when someone - usually a child - asks me a question starting with the word 'why?'... and I cannot answer.
Your question appeared so easy to answer until I tried. So here is a collection of statements because I cannot put them in definite order.

1. All of mankind's needs were satisfied by plants.
   Food, shelter, fuel, clothing, medicine.
2. Man is the most adaptive of all creatures.
   He can alter his environment to the extent that he can live anywhere on earth.( I believe that the cockroach may be the second-most adaptive creature.) Man had to learn to husband animals and crops to defend against famine caused by drought, flooding, plagues and the like
3. I imagine that water conservation would have been his chief concern. It was essential to him, his animals and his crops.
4. As populations grow and crop-lands become more scarce the need for better crop production becomes acute.
   Plant breeding and irrigating/water conservation methods are the chief means of maintaining an adequate world food supply.
   Here is a link to the beginnings of drip irrigation. I include it because, long ago and far away, I was fortunate to listen to Dr. Goldberg on the subject of drip irrigation
   And as a spin off, you and I can buy an Aglaonema "Crete", and place it anywhere in the house and keep it alive and healthy because we know to water it.

This post was edited by ronalawn82 on Sun, Nov 3, 13 at 20:41