Most vegetables tend to get spoilt after a few days of harvest. Even studies on post harvest physiology don't confer alot of benefits due to their perishable nature. The one vegetable that lasts long is the pumpkin family, to be specific, butternuts. They can last for years and one can wait for prices to stabilise before selling. One simply needs to store them in a cool dry place to make sure that microorganisms do not get the better of them to destroy their long shelf life.