Each house has a certain amount of space/slots for objects, including plants. Most of the crown houses have space for 250 objects outside and 250 inside. So in this house you could theoretically plant 125 plants (plots count as a slot and so do seeds). Other houses have different amounts of space/slots.
50 plants is a lot and I find it hard to believe you have enough plant/green energy to tend to them all.
Though house size and placement have some baring on garden size, it is essentially how much you want to spend on crowns to refill energy. Each plot counts as 2 items in your house, one for plot/planter the other for seed/plant. So about 100 slots used inside or out. That many spaces seems excessive for one house unless you have a miraculous grouping a/o made of crowns. But best of luck to you and your gardening ventures, even if you have best gardening cards you will be hard pressed to take care of all of them.