Long growing season and cutting back dahlias

tobi

So I overwintered my dahlias. I’m in North Georgia - zone 8a. They were blooming by the end of May and finished around the end of June. As you can see, I’ve whacked them down. I did this last year with a few as a test run and it worked perfectly fine. So, if dahlias need 120 days to make tubers. And mine have been in the ground since last year, there is already a giant clump in the ground. And should be making new ones as we speak, right? Since I’ve whacked them all down, am I getting growth from both new AND old tubers? Or just old? Someone had asked me if I worried about the tubers running out of energy with such a long growing cycle. So thought I’d come here to ask.

SteveM

tobi Your tubers will continue to grow and multiply when the new growth starts. Since you left some nodes(and not cut at soil level) the new growth will come from that point and not from eyes on the tubers (usually).The method you are using is sometimes used to clean up insect infestations (e.g., spider mites). It is also used to get a Fall flush of dahlias in areas with hot summers.

One thing to watch out for using this method is to make sure the tubers are not getting baked in the sun. It looks like you are using mulch so this might not be a concern. You have cut down the canopy which was shading the tubers so if you can feel tubers close to the surface you might want to provide some sort of shade until the new growth is providing shade. Also if you are watering, this is a time to make sure you do not over-water the tubers

Teddahlia

Here in the PNW we have no experience with your method. We plant and they bloom until we dig them in October-November. When dahlias are left in the ground, the clumps have tubers of different ages. The "over winter" people seem to be two types: Those who do nothing and the plants grow or die and have multiple shoots. They may dig them every few years.
The other "over winter" growers do a version of "digging" in the spring where they harvest some tubers but put the clump back into the ground and control the clump to only allow 3 or 4 stalks.

I do not understand cutting them back now unless you are trying to get two bloom seasons like some grower in the South do. The question about "energy" in tubers seems sideways to me. Dahlias get their energy mostly from fertilizer and the tubers just have a minor amount that get the sprout started. But all of my comments are speculation as we do not have your climate here.

tobi

Teddahlia well there were a few reasons for cutting them back. They bloomed like crazy and did great. However, the temps for past few weeks have been in the mid to high 90s. And no rain. The dahlias had basically stopped blooming, and the heat is just too much for them. So I cut them back. They already have new growth, and based off trials I did last summer, they were back to blooming in about 8 weeks and then went until frost, which is mid November for us.

So I guess the “energy” part of my question was more from someone else. They were curious if they run out of “steam”, thinking that once they have grown into plants, and bloomed, by me cutting them down, will they actually have enough to keep them going.

But the other part of my question was more about tuber creation. And since they’ve been in the ground so long, even if you use March as the jumping off point - since that’s when they started to emerge, does the 120 day rule with new tubers starting to form mean they are capable of sending up shoots from those new tubers now, and not just the old ones.

Teddahlia

Tubers start out small and grow bigger to the size set by the genetics of the plant. The viability of the tubers is more by size than maturity. Most of us have some very small tubers on clumps and when the variety is in short supply we attempt to save them. Many shrivel up and do not store. The ones that do make it can be sprouted but not in the ground but rather in a pot with good potting soil. The 120 day rule is just a myth and no one could predict how many days it takes as the weather is different in different places.
In your cutting down of the stalks, you made those tubers into "second year" tubers and the new growth will make new tubers. The "second year " tubers will get a bit bigger. The new tubers will be in many cases too small, but some may well be big enough. You will have lots of tubers.

tobi

SteveM thanks for the info. I do have a layer of leaf mulch on top and the soil is cool underneath. I do know what you are talking about with them steaming in the beds. I have had that issue when I first started growing and didn't pre-sprout my tubers. if they are actively growing, I don't seem to have that problem.

calico20hill

Steve's advice is pertinent to us in the PAcific NW as well, when we get these "Heat domes" over us, (Something I never encountered to this level in my many past years in the area). In my raised beds the tubers got semi baked, and with watering I think they got stewed as well! I grow in raised beds because the native soil is solid clay. But in the ground the heat may not have been as intense. I am hoping our current heat wave will be the only one this summer, dreamer that I am! I have also cut back some on watering to prevent the soil being hot and water logged at the same time. It is 93 degrees at 10 AM so we will see the results of my strategic moves pretty soon.

tobi

calico20hill we are also having an abnormally hot summer and have been stuck in a heat dome for some time now. I am hoping it decides to move along!