The king & 3 sons

The King & 3 Sons
A wise King wants an honest child to take his place on the throne.

He gives each of his 3 sons a pack of flower seeds and tells them that the one who grows the most beautiful flowers from these seeds will have his throne.

Six months pass and the king checks the flowers.
The first 2 had beautiful flower beds while the last child had nothing in his plot but weeds and no flowers.

Yet, the king chose this child to have the throne.

Why?

The 3rd son was the only one that didn't cheat. The King had baked the seeds so they wouldn't grow, which means the first 2 didn't use the seeds from the packet he gave them.