Simple Rhymes:
* Plants: "Grants", "Slants", "Pranks", "Trants" (not a real word, but a playful rhyme)
More Descriptive Rhymes:
* Twigs: "Brigs", "Shigs" (informal)
* Leaves: "Believes", "Grieves"
* Stems: "Gems", "Dreams"
* Blossoms: "Booms", "Toms"
* Seeds: "Needs", "Pleads"
* Sprouts: "Outs", "Routes"
Playful Rhymes:
* Bits: "Fits", "Wits"
* Pieces: "Peaces" (a play on words)
The best rhyme will depend on the specific context of your writing.