The oven was the reward of this event at (and only at) the year 2012. They didn't do it for the last two years. So basically so far we don't know how could we retrieve the oven. But if he does turn it on (and hopefully post a news to let us know), all you need to do is to 'trash' a plant that you've already had to get the reward. It will not affect your pot vacancies. Personal tip: Just keep collecting event seeds because it has many variants
Oh okay. I hope it is turned on as I would like to get the oven for that garden. I will do just that as long as the event keeps going. So how do we get the table and other items for that garden?