Greenhouse Fruit
You can purchase fruit seeds from the Tropical Barter, Nordic Barter or Voucher Booth events whilst the temporary farms are running. They can be grown in the greenhouse. Production can be increased by 25% by adding special greenhouse humus, available from the Special Press production machine. The special seeds work out slightly cheaper and are a good deal faster to grow, so as soon as you have the shells/runes available, buy them.