Flower · Asteraceae
When to plant zinnias
Zinnias are warm-season flowers. Choose a sunny spot and wait for suitable outdoor warmth; seedlings raised under cover still need a gradual transition to outdoor conditions.
Start seed indoors
4 weeks before
Counted from your last spring frost.
Plant out
1 week after
Counted from your last spring frost.
Sow direct
1 week after
Counted from your last spring frost.
Choose a place for estimated dates and local climate checks.
Timing, in frost-relative terms
These offsets are the starting assumptions used by our calendar for zinnias. They do not establish suitability in every climate. Your seed packet, cultivar and local growing advice take priority; in frost-free places the calendar uses monthly temperature patterns instead.
- Start seed indoors 4 weeks before the last frost.
- Plant out 1 week after the last frost.
- Sow direct 1 week after the last frost.
- Expect 60–80 days to maturity, counted from sowing.
- Sow again every 21 days for a continuous supply.
Getting the timing right
Dwarf and tall varieties serve different purposes. Pick a compact type for a patio pot, or a taller variety if you want stems for cutting.
Frost tolerance
Check the named variety and local forecast before exposing young growth. The catalog cold-damage figure is a reference, not a guarantee: plant age, acclimatisation, wind and the duration of a freeze affect damage.
Classified as tender, with a catalog cold-damage reference of 0°C (32°F)32°F (0°C). Exposure duration, growth stage and acclimatisation change cold tolerance.
Before you plant zinnias
Use the calendar to plan ahead, then check the conditions in your own garden.
- Measure the soil at sowing depth. Aim for at least 21°C (69.8°F); the calendar estimates soil warmth from air temperatures and cannot measure your bed.
- Check the local overnight forecast before planting out. Delay planting or keep protection ready if frost is forecast, even after the historical last-frost date.
- Harden off plants raised indoors: gradually expose them to outdoor light, wind and temperature before their final move into the bed.
- Use the maturity range on your seed packet when choosing a variety. Cold, short days and transplant stress can make harvest later than the calendar estimate.
Warmth, sun and a variety that fits the space
Dwarf and tall varieties serve different purposes. Pick a compact type for a patio pot, or a taller variety if you want stems for cutting.
Allow the spacing recommended for the variety. In humid conditions, choose a disease-resistant type where available and leave enough room to inspect and tend the plants.
Treat the local calendar as a seasonal starting point. The flowering result will also depend on light, water and the length of the warm season after planting.
Growing in a container
Compact zinnias suit sunny containers with drainage; choose the variety by its mature height rather than the size of the nursery plant.
Further reading: RHS zinnia growing guide . General crop guidance; local dates on this site are calculated separately. Source checked 18 September 2026 by Safe to Plant; this is not an expert review.
How the dates are calculated and their limits · Keep a growing record · Report a local discrepancy