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.