In order to get Jacks and Giants you need treasure as food and a fully grown beanstalk.
If you plant a toadstool in the golden pot that you have in your garden at the moment then you can attract the fairy which when spotted will put treasure on an empty plate.
However, if you plant a toadstool now, then it will take at least 24 hours until it is ready for harvest to attract the fairy.
I would suggest to have a look at the following thread which is a great help and explains the fairytale in more detail:
https://www.fairylandgame.com/fbfairy/forums.php?tid=71350
