Here’s a chart showing the seed starting and garden planting dates for Billings, Montana USA. If you are going to err, err on the side of a bit LATER rather than earlier when starting seeds or setting out seedlings… late cold snaps can be deadly to tiny plants!
Keep in mind that our Average Frost Free Date is May 15, and Earliest Average Frost date is September 15. This means that we have a fairly short but definitely INTENSE growing season. Those long Montana summer days really pour on the sunlight to our gardens, helping them out-produce many gardens much further South! However, very long growing cultivars are to be avoided (or protected). Note the “Days to Germination” and/or “Days to Harvest” printed on seed packets or seedling inserts. Most of our plant nurseries in town are good about bringing in cultivars appropriate for our climate, but some product from the bigger warehouse-style stores (naming no names) need to be checked a bit more closely. For that matter, you need to check seedlings from the superstores very closely, and be careful to let them “harden off” well before you plant them. The strong drawback to a cheaper seedling is that there is a reason they can offer them less expensively, and that often means the seedlings aren’t as hardy or healthy as you would like, potentially setting them back severely once planted or even causing plant death. Yet another time when “Buy or Grow Local” is important!