There's a huge difference in how long plants will live if you don't give them what they need to grow. Seeds can live a long time. The oldest seed that germinated is a 2000-yr-old date palm seed. There's an internet site that says seeds from corn, beans, and lettuce last 2-5 yrs.

Young plant seedlings will die in a few days or less if they don't have water or light. Older plants will live longer without water or light before they die. Another problem for plants is that they can die if they get too much water. Too much water drowns the plants, because their roots root and don't get enough oxygen.

There's no simple answer to how long a plant will live without light and water [and air!], because there are so many different kinds of plants and trees. Desert plants like the saguaro cactus can live over 100 yrs with little water. It would probably take more than a year for a saguaro cactus to die without water.

Some scientists did an interesting experiment with young pine trees. They kept them in a greenhouse with no water. The first tree died in 29 days - less than a month. The last tree died in 147 days - almost 5 months! I don't know how old the young trees were when they stopped being watered or how many trees there were.

Thank you for your question - it was a hard one!