For me, it's Fickle Pickle. One time, it asked for FOUR NEEDS AT ONCE. Music, Magic, Sun and Pollination. What do you think is the hardest plant to grow?
None are hard to grow some just take longer then others. When you say hard if you are meaning longer then i would say red bell peppers they take forever to grow even with 5 likes.
They often require all five spells and enchanted medium plots. I have also seen them with lvl 4 Pests.
If you have a weapon rack (you can craft it from a recipe in Marlybone.) It will grow faster but its unpredictable. Sometimes it will give you a new seed, sometimes not. Often it does give a sunfruit though.
Grandmaster Gardener x2 and , Love the Red Barn Farm
Plants that are really had for me I have not yet seen or dealt with them, but, if you mean all my plants at once, that is hard. I have a lot of stinkweed, and about eight boom shrooms, one which disappeared once at elder :(. Each of them needs things each day, and that takes a LOT of my pet energy.
Fish on a Vine typically get rank 4 or 5 pests on the second day of maturity. If you're not there yet in terms of spells, you will just watch helplessly as your things die.