Dahlias forum: Dahlias in the Southeastern US?

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Name: Virginia
Charleston, SC (Zone 8b)
Köppen climate classification Cfa
Sep 1, 2018 3:56 PM CST
I have read in a number of places that Dahlias don't like heat and humidity, so aren't recommended for my area. I'm usually skeptical of Gardening Rules because I seem to have unwittingly broken a few of them, but on the other hand, I don't like to waste money on plants that are not supposed to do well here.

This spring I bought a couple of dahlia tubers at Aldi's for about $5 (for both). It seemed like a good price for experimenting with a new genus of plants. Not expecting much success, I planted them in 3-gallon nursery pots with my own potting mix, and left them to their own devices.

They are now both quite large. One, 'Crazy Love', even bloomed the other day despite being in a pot that was too small. It got moved up to a much larger pot today, and staked. It has another bud, and since we shouldn't get a freeze until December or January, I'm thinking I may get a few nice-looking flowers, despite the early neglect.

The other plant, 'Vancouver', looks healthy, but is a sprawly mess in its too-small pot. I plan to transfer it to a larger pot also, but don't know if I'll get any blooms this year. I may want to keep it in a (larger) pot until it proves that it will bloom here.

My question is about what to do going forward, now that I know that dahlias (at least these two) seem able to cope with our heat and humidity. Presumably, they'll die back once winter weather arrives. Do I cut back the foliage, or leave it to "feed" the tubers? And since I'll want to plant them out, when will be the best time for that? Later this fall, during winter dormancy, or in the early spring?

Any advice is appreciated. My zone is officially 8b, but I think we're "on the cusp" of 9a.

Thanks in advance,
Name: Frank Richards
Clinton, Michigan (Zone 5b)

Garden Ideas: Master Level Celebrating Gardening: 2015 Plant Identifier
Sep 1, 2018 4:59 PM CST
I am in zone 5-6, so I know nothing about dahlias in zone 8-9.

That said, it seems to me that you could plant your dahlias now. They are hardy in zone 8-9 and will be fine over the winter.

Side note, dahlias originally come from Mexico. Here in Michigan, I have to dig up the tubers and store them in the clear over winter.
Name: Geof
NW Wisconsin (Zone 4b)
Region: Wisconsin Dahlias Garden Ideas: Level 1 Celebrating Gardening: 2015
Sep 1, 2018 5:15 PM CST
Its not that Dahlias wont grow in hot areas, but that they dont bloom well in the heat.

However, I know of a gentleman in FL who grows lots of dahlias regularly. I believe he plants them out early (Feb?) gets nice blooms in the spring early summer, then they go kind of dormant during the worst of the heat, and begin blooming again when it cools down. He does dig his every year or two to divide the tubers.

I would advise growing them in the ground with lots of mulch to keep them as cool as you can.

Good luck!
Name: Virginia
Charleston, SC (Zone 8b)
Köppen climate classification Cfa
Sep 1, 2018 5:59 PM CST
Thanks for the good info. I guess I will wait on 'Vancouver' to see if it will bloom in our climate.

I was surprised at the difference in habit between the two varieties. 'Crazy Love' seems to be much more tall and upright, and really didn't start to lean out of its pot until recently. 'Vancouver' didn't ever seem to be interested in growing up, but got pretty floppy early on.

As for planting now, the plants might be okay with that, but I'd rather not bother with it until the weather cools off a bit more, and I figure out where I want them to go.

Thanks again,

Name: Sunshine
Hillsborough, NC (Zone 7b)
Oct 14, 2018 10:22 AM CST
scvirginia, dahlias handle heat fine. If they're healthy and cared for thoughtfully, they'll still bloom from late spring until the first hard frost.

If you're worried about the humidity, space your plants a few inches farther apart than the label recommends, keep the stems clear of leaves up to 6" off the ground, and stake with a raised grid, such as a peony support ring, instead of with a stake. Air circulation is what's critical, and grids hold the stems up and apart instead of bunching them together. (ex. https://www.plantsupports.org/...) Finally, if the soil is prone to waterlogging in your area, plant in raised beds at least 8" above soil level.

As far as winter care, dahlias need digging up and storing for winter if the soil temperature gets below freezing in winter, or if winter precipitation is too high. For example, I rarely need to dig my dahlias here in NC, zone 7b. Last year though, we had a late spring winter storm. First, twelve inches of snow lowered the soil temp. Then, all that snow melted and the icy water saturated the soil for several weeks. My entire field was a rotten mess, and what hadn't rotted had moved around (away from labels labels) in the mud and slush. If you expect to get more than frost where you are, then you dig and store. If not, then you dig, divide and replant. Dahlias need the down time like a lot of other tuberous perennials, so chill time is fine, as long as it's dry.

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