The most common "gift" for the teacher from the student is 寄せ書き（よせがき） if you want to know. Each student writing a card or letter separately is nice but we usually go for this in Japan. Each student writes a small message on it. It's also easy for the teacher to keep.
In Japan, it's not common to give teachers gifts of monetary value unless:
1. The teacher is retiring or
2. The teacher is relocating long-distance.
Then again, this isn't in Japan so you could add a plant or cakes as you said.
Just remember that if you are doing the 寄せ書き or an individually-written letter, make sure to present it the way that that is the main gift, not the other thing (plant or candies).
