When to sow bamboo seeds and transplant?
Bamboo Sowing Season and Transplantation
Certified GKH Gardening Expert
This, completely, depends on your location. You can start them indoors at any time, But I would transplant when there is no chance of frost in your area.
This article will help on the care of bamboo: https://www.gardeningknowhow.com/ornamental/foliage/bamboo/caring-for-bamboo-plants-in-your-garden.htm