Frederick the Great ordered potatoes – he did not guard them.
On 24 March 1756 Frederick II instructed his Silesian officials to promote potato growing, calling the crop useful and a help to poor farmers. The popular story of soldiers pretending to guard potato fields to provoke theft and thus spread the crop is a legend with no evidence behind it.
Useful: When an anecdote is too clever to be true, it usually is exactly that.
Source: de.wikipedia.org