To become an illegal gardener, you need to get an underground greenhouse. This will be your little "green" empire.
How to Access the Underground Greenhouse?
First, rent a garage. Then purchase the Underground Greenhouse upgrade and go to the garage exit — and the greenhouse is yours.

What Can You Do in the Underground Greenhouse?
Here, you can grow and sell sprouts. There is also the Upgraded Underground Greenhouse upgrade, which makes plants grow 30% faster. But be careful — pests can slow down the process.

How to Start?
You will need seeds. You can get them at the gardener job by digging up potatoes. Seeds are stored in your inventory.
How to Plant?
Walk up to a pot and tap Plant. Then wait for the sprouts to grow. Without upgrades, this will take 12 hours. With the upgrade, it will take 8 hours and 40 minutes of in-game time. Remember: time only passes while you are in the game.

What Should You Keep in Mind?
Water the plants every 2 hours, or every 1 hour with the upgraded greenhouse. Otherwise, their growth will stop.

How to Sell?
To make money, you need to sell your harvest to one of the gangs.
In the greenhouse, choose the gang you want to sell to. Find the NPC near that gang's base and talk to him. The price per item ranges from 250 to 300 units of in-game currency.

Sell it, get paid, buy new supplies — and get back to work!