You’ll get the best sunflower blooms in Michigan if you plant after danger of frost has passed, usually from mid‑May through early June, once the soil is warm.

Ideal planting window

  • In much of Michigan, the last frost is around mid‑May, so sowing outdoors from about May 15 into early June is a safe bet.
  • In warmer southern areas you can often start a bit earlier (late April–early May) if the soil is workable and frost risk is low.

Frost and soil temperature

  • Wait until nights are consistently above freezing and the soil is no longer cold and soggy, which typically lines up with late April to mid‑May depending on your part of the state.
  • Sunflower seeds germinate best in warm soil; cold soil can rot seeds or stunt seedlings, leading to weaker plants and smaller blooms.

Staggered plantings for longer blooms

  • For flowers through most of the summer, you can sow new seeds every 2–3 weeks from mid‑May into July, as long as your variety can mature before the first fall frost (often late September or early October).
  • Many common sunflower varieties bloom about 60–90 days after sowing, so later plantings will give you late‑summer or early‑fall color.

Starting indoors vs. direct sowing

  • If you want a head start, you can start seeds indoors in biodegradable pots in mid‑to‑late March, then transplant outside after frost danger has passed (usually the second half of May).
  • Many Michigan growers simply direct‑sow outdoors around May 15, spacing seeds about 6 inches apart and 1–1.5 inches deep in full sun.

Regional tweaks within Michigan

  • Southern Lower Peninsula: Often safe to plant late April to mid‑May; you’ll get an extra‑long season if you also keep sowing into June.
  • Northern Lower Peninsula and Upper Peninsula: Lean closer to late May–early June, because last frost and cool soil stick around longer there.

Quick HTML table: sunflower timing in Michigan

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Region Typical first outdoor sowing Last sowing for good blooms Notes
Southern Lower MI Late April–mid May Late June–early July Warmer; can experiment with earlier planting in warm springs
Central Lower MI Around mid May Late June Common “plant after May 15” rule of thumb
Northern Lower & U.P. Late May–early June Early July (fast varieties) Shorter season; choose 70–80 day varieties
If you share roughly where you are in Michigan (e.g., Detroit area, Grand Rapids, U.P.), I can narrow this down to specific weeks and suggest a couple of varieties that fit your season length.