When can I start planting in a green house?

Where do you live?

where are you located? Is it heated? does it have lighting?what do you want to grow veggies?flowers?specialty plants? here's bunch of videos to get you going, start watching https://www.youtube.com/results?search_query=diy+starting+a+greenhouse

Call or visit your local nursery to get more information for your area.

Hi Connie - This is the ultimate and super easy step-by-step guide to determine your plant hardiness zone, your frost dates, and also when to start planting indoors and outdoors. Plus lots of great resources. Hope this helps and happy gardening! Hugs, Holly

https://pinkfortitude.com/sow-and-plant-seeds/