There is no ban on "shorting" onions specifically - it is just not traded on the futures market at all. Gerald Ford pushed through legislation on behalf of onio

There is no ban on "shorting" onions specifically - it is just not traded on the futures market at all. Gerald Ford pushed through legislation on behalf of onion farmers in the late 1950s to disallow it on the futures market. It has been an example of extreme market volatility ever since.