In Michigan, the best time to plant tomato transplants outdoors is around late May, typically around Memorial Day, once the risk of frost has passed and the soil has warmed. This usually corresponds to the last week or two of May. Tomato seedlings can be started indoors about six to eight weeks before this outdoor planting date, which means starting seeds indoors in early to mid- March. In cooler northern parts of Michigan, where the frost lingers longer and the growing season is shorter, tomato planting may be delayed until late June to early July. In this late planting scenario, fast-maturing and determinate varieties are recommended to ensure a timely harvest. Planting by late May to mid-June is ideal for most areas of Michigan to ensure that the soil is warm and the evenings are generally frost-free, allowing tomatoes to develop well.
