You can plant dahlias outside safely after your region's last frost date has passed. This is typically when the soil temperature is warmed to above 60°F (around 15°C), which for many regions falls between mid-April and May for planting dahlias outdoors. For colder or wetter climates, waiting until late May or even early June may be necessary to avoid frost damage and tuber rot. Key points to consider for planting dahlias outside:
- Wait until after the last frost date in your area.
- Ensure soil temperatures are warm (usually above 60°F).
- Planting too early risks frost damage and tuber rot due to cold, wet soil.
- Tubers can be started indoors earlier and then transplanted outside once conditions are safe.
- In some regions, late planting close to mid-May or early June is common, especially in cooler areas.
For example, many gardeners plant dahlias outdoors around Mother's Day (early to mid-May) in milder climates, but in cooler places like Canada’s Zone 3a or the Pacific Northwest, it might be best to wait until early June or when the risk of frost is minimal.
If you want to get a head start, you can start dahlia tubers indoors in pots in March or April and then transplant them outside after the last frost.
So to know your specific planting date, check your local last frost date using weather data or regional gardening groups, and then plant dahlias outside once that date has passed and the soil is warm enough.
