you can't plant stock options in the ground

Stock options are very different from stock shares. I assume you're talking about shares.

Stock shares represent part ownership of a company. The fact that you're likely to be a minority owner and have no control over the company does not change the fact that you are still legally entitled to a share of the company's value. If the company's value rises, the value of your share rises as well.

it is possible that a transaction is positive sum

If you're talking about personal subjective utility, every voluntary transaction is positive-sum. But that's irrelevant for the purpose of this discussion since here we are talking dollars and not utilons.

therefore the stock market is approximately zero-sum

You still don't understand. Public companies (generally) create value. This value accrues to the owners of the companies who are the holders of stock shares. In the aggregate, stock holders own all the public companies. If the public companies produced value, say, this year, the value of the companies themselves increased. This means that the worth of the stock in the stock market has increased -- even if no transactions have taken place. That is why stock market is not a zero-sum game.