You should plant sunflower seeds in spring, after the risk of frost has passed , when your soil has warmed up.

Best planting window

  • In many temperate climates, the main window is April to May outdoors.
  • Some guides allow sowing from early March to mid‑May if you start seeds indoors where they’re protected from frost.
  • You can usually sow as late as mid‑June , but late sowings may flower closer to autumn.

Temperature and frost timing

  • Sunflowers are a warm‑season annual and prefer soil around 55–60°F (about 13–16°C) to germinate well.
  • Wait until all danger of frost has passed before planting them outside or transplanting indoor‑started seedlings.
  • If you’re unsure, a simple rule: plant when you’d be comfortable planting tomatoes outdoors.

Indoor vs direct sowing

  • Starting indoors:
    • Sow from early spring , 2–4 weeks before your last expected frost, in small pots.
* Keep them in a bright, frost‑free spot, then harden off and transplant once nights are mild.
  • Direct sowing outside:
    • Sow from mid‑April or May , once the soil is warm and workable.
* Many gardeners simply wait for consistently mild nights and then plant straight into the ground.

Quick depth and spacing tip

As a handy example: plant seeds about 1–1.5 cm (around ½ inch) deep , in a sunny spot with well‑drained soil, and thin or space plants so each one has room to reach full height.

TL;DR: For most home gardens, plant sunflower seeds outdoors from April–May after frost , or start indoors a bit earlier and transplant once it’s reliably warm.

Information gathered from public forums or data available on the internet and portrayed here.