Quora is a site for posting questions to the internet. Sometimes those questions get answer. For example Robert Frost, who has trained astronauts for the International Space Station, has answered the question: How are plants growing in the ISS?
Gravity is not the only difference between the Earth environment and the ISS environment. In the closed atmosphere of a spacecraft, volatile organic compounds (VOCs) can accumulate. VOCs need to be scrubbed from the air or seed production will suffer. There are elevated radiation levels that can cause mutations and affect growth. An experiment on Mir, that involved storing tomato seeds in space for six years found mutation rates up to 20 times higher in the space seeds than in the control seeds stored on the ground. And there are the spectral effects of using only electric lighting.
Because plants also respire, we have to have fans to circulate the air around the plants so that they don’t suffocate on their own exhalations. Even failed experiments can provide us with better understanding. An experiment to study plant lignin failed to produce healthy plant materials but taught us more about providing effective air movement.
You can read more at Quora.