Suz suggested I post this curriculum called TurfMutt Discovery/OPEI Education program (full disclaimer: I work with them!). It's a free plant science curriculum for grades K-5 that helps get kids excited about science using their own surroundings, backyard, local parks, etc.
Here's the link to download the lesson plans, divided by age group. It is meant to get kids back outdoors and involved in STEM education. Enjoy!