In Michigan, the best time to plant annuals is generally after the last frost date to avoid damage to tender plants. This typically falls around mid-to-late May. For example:
- Northern Michigan (USDA zones 6a to 6b): Safe planting time is mid-to-late May once overnight temperatures stay above 50°F.
- Southern Michigan (Downriver region): About two weeks after the last frost, around May 12.
- In general, last frost dates in Michigan cities range from early May (around May 2-6 in Detroit, Dearborn) to mid-May and later in some northern areas.
Early April can be used for cold-hardy annuals like pansies and violas that tolerate cooler temperatures and occasional frost. Tender annuals like petunias and marigolds should wait until temperatures are reliably warmer around mid-May. Gardeners often wait until Memorial Day weekend to plant tender annuals outdoors to be safe from frost, though some may start earlier with protection or by hardening off plants by keeping them indoors nights initially. So, for most Michigan gardeners, the ideal planting window for annuals is mid-May to Memorial Day, depending on local frost dates and the hardiness of the plants being put out.
