Making sure the plants have enough sunlight and a proper airflow is a good place to start. You don't want plants growing in a stuffy environment, and I find that a lot of people don't have regularly clean enough rooms to avoid stale air. If the plants can't be placed by a window, then buying UV lights can help - however, they are obviously bright and warm. If you live in an area where marijuana is prohibited, be prepared to be able to properly and sufficiently identify your vegetation and herbs so you're not mistaken for growing weed (I mention this becuase I live in a less than desirable area where crime is high).
Other than that, research what you are growing and make sure it has the proper dietary needs, including the right amount of light/shade, temperature, humidity levels, etc. It's easiest to research where the plants grow naturally and just follow suit for the environment you're growing them in.
I remember Isadora worked with bats, so she probably knows that guano (their droppings) can help fertilize soil to make plants grow more easily. If you can afford a worm environment (it looks like a standing cauldron filled with dirt), growing your plants there and feeding the worms things like egg shells and banana peels helps. Just make sure that you don't have too many worms or too many plants and keep in mind that heavy water brings the worms to the surface.
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