Hint
If you control the harvesters on the LED fields, and you only let them harvest 200 units from a full flower and tell it harvest from a different flower, the flower never gets used up and therefore grows back. So you never have to replant the field. The total amount you get from a full grown flower is 250. Keep it below that and the flower grows back. If you keep this up then one little field of LED will give you endless money. Plus you don't need to use many seeders and you don't have to wait for the fields to turn over. Since the game gives you a little field to start out with then you will always have a lot of money.
