The resourceful mycologist (that's a fungi-studier) Paul Stamets has made cardboard packaging that can be planted and will grow into trees. It's called the Life Box.
The Life Box suite of products builds upon the synergy of fungi and plants by infusing spores and seeds together inside of packaging materials that can be planted.
The Tree Life Box is made of recycled paper fiber. In this fiber, we have inserted a wide variety of tree seeds, up to a hundred, dusted with mycorrhizal fungal spores. The mycorrhizal fungi protect and nurture the young seedlings. For millions of years, plants and beneficial fungi have joined together in a mutually beneficial symbiotic relationship.
You can get started by simply tearing up the box, planting in soil, and watering.
Here's a video of Stamets (wearing a hat that makes him look a little like a mushroom himself) explaining how the Life Box works on local San Francisco news.
If you run a company that could use these instead of normal cardboard, I will happily post about how responsible you are if you pledge to switch to these things. Just drop the details in the comments.