That short answer comes from the developer FAQ. Every room and balcony has its own environmental conditions, so two nearby positions can behave differently. The same source says some plants can only be grown on the rooftop.

Diagnose one variable at a time

  1. Open the plant’s current condition display and confirm the warning is light, not temperature, soil, water or disease.
  2. Move the planter to a different position or growing area and recheck the condition.
  3. If the location must stay dim, use an in-game grow light. Do not assume ordinary decorative lamps change the plant simulation.
  4. If attaching a grow light or cooling fan, a developer reply says the target must be a larger 4×4 planter and the plant must still be at the smaller-shoot stage; an onion planter is the example given.
  5. If the new position is too bright, use a shading net.
  6. Recheck temperature after moving. The developer says balconies are warmer than rooftops but colder than indoor spaces, and temperature also changes with season.

The reviewed sources do not give numeric light thresholds or a fixed number of grow lights per plant. Do not promise that a particular lamp count solves onions or parsley. Match the in-game condition indicator for that species and patch.

There is no game-over state according to the FAQ, so a wrong placement is a diagnosis problem rather than a lost save. Still, a plant can suffer if its needs remain unmet; correct the warning instead of waiting indefinitely.