Wondering when to plant dahlias outside in your local climate?
It is typically considered safe to plant your dahlias outside after your region's "last frost date" has passed. This date is an average of when the last spring frost occurs, and is different in every region.
How To Determine the Average Last Frost Date in Your Climate
Last frost dates can be determined using average weather data provided by NOAA National Centers for Environmental Information. Also, many websites provide tools where you can look up your last frost date by zip code (like almanac.com or davesgarden.com).
However, in my opinion, the best way to find your regional last frost date is by asking your gardening neighbors. They'll know your microclimate better than any other resource! You can also post on regionally specific gardening Facebook groups for additional tips.
...But Can They Actually Be Planted Out Earlier Than That?
Interestingly, I have known local dahlia growers who plant their tubers out a few weeks before their regional last frost date. This is not something I typically recommend to my dahlia tuber customers because of the risk...
However, I actually plan on experimenting with planting about 2 weeks earlier this year, just to see what happens. I have heard of enough local growers doing this to feel like it’s worth the experiment. I’ll continue to instruct others to wait until their regional last frost date to be safe, until I feel confidant planting earlier, myself.
Get a Safe Head Start By Planting Dahlia Tubers Early, Indoors or Under Cover
Of course, you can start your dahlias earlier indoors, then slowly harden them off (to get them used to being outside), and transplant them out after the last frost date.
Greenhouses, hoop houses, row covers, or cold frame like lids for raised beds can help, too.
Prevent Dahlia Tuber Rotting: Pay Close Attention to Predicted Rainfall
Another factor that could influence your chosen planting time is the predicted rainfall. Dahlia tubers are very susceptible to rotting, especially when first planted, and until they start growing.
I've had it dump rain right after planting and not had any trouble, but I'm lucky to grow on a slight slope, with soil that drains relatively well.
Keep this in mind! The location of your dahlia patch, soil drainage, and weather forecast can influence your planting time.
For My Vancouver, WA Followers...
For my local followers growing dahlias in Vancouver WA, I’ve heard gardeners say that it’s time to plant frost sensitive plants after the snow has melted off the local mountain commonly called “Silver Star.”
Since I’m a bit farther northeast, my last frost date is later (generally considered the third week of May).