How cold does it get where you are? I wondered about this too (posted about it maybe a month ago) asking if anyone in the EC left tubers in the ground to overwinter with success.

If you plant them 7" won't they not come up--this is my first year so I have no idea but everything I have read says plant them only a few inches under the soil. I was considering attempting to overwinter a bed but by putting stuff on TOP of the bed and then clearing the bed in spring vs planting the tubers deeper.

Anyway curious to hear your thoughts, interesting about your forgotten tuber!

**portia: We typically get our first hard frosts in late Oct - early Nov in the early fall. In the winter our lowest temps can get to single digits F, but typically the lows are in the high teens to high 20's F. The average high in Jan and Feb can range from 30-37 degrees F, but we can have some days colder or warmer than that.

For us we can still get frosts at night til late April to early May at the latest, but normally most nights the low temps dont drop below 32 degrees F by late April. That means the best time to start dahlias outdoors here is in mid to late May, or early June if its cooler.

As far as how deep to plant them, I will include this short video from Swan island dahlias about planting. I bought most of my tubers from them, and I followed their instructions. I grow larger dahlia plants that get between 4 feet to 6 feet tall, with flowers from 3.5" to 7" wide, and according to Swan Island the best planting depth is 6 inches. So I dont think an extra inch would hurt, and I think it would probably insure they are below frost line. Also a layer of some sort of mulch may be a good idea, and it can be removed in early to mid May.

https://www.youtube.com/watch?v=n-FvUm1Cy6s

Here is a link that might be useful: Video on planting dahlia tubers

In warmer climates, a lot of people leave Dahlias in the ground, only digging them every 2-3 years to divide them. I think its important to have not only warmish winters, but very well draining soil. Cold and wet and they will tend to rot.

I didn't realize Delaware was so warm. In Wisconsin digging and storing inside every fall is the only option.

re: rot I've amended the soil in the beds very heavily with sand as we can get huge drenches of rain here, I started my tubers in pots and a few of the pots even with good potting soil was holding onto the moisture and a few tubers were getting soft from being saturated too many times.

I may overwinter some this year just to see how it goes!

To: portia,

That was exactly the same circumastance I went through the last 2 years with dahlias. We got LOTS of rain last year from April through July, into August, which is odd considering it normally starts getting dry in June in the mid Atlantic. So even though I used a mix of potting soil with gardening soil and some native soil, it was waterlogged, so I had to replant twice last year.

This year I assumed we wouldnt get all the rain we got last year, but in May we had a huge storm that dropped inches of rain and when I looked at them the next day, it was like digging a hole in the sand at the beach, when you dig deep enough you run into water. Well, all I had to do was dig down 3 inches around the dahlia tubers, and I was hitting water!

So I dug them all up, buried the sopping wet soil back into the hole, but got rid of about an inch of it, then made a new mixture of about 50% sand, built mounds roughly 6-7" tall and buried the tubers inside the mounds at about 1" above normal ground level, so that in reality they werent deep enough to become covered in water again.

They dont like being dug up & replanted after they have been in the ground a few weeks, and it caused them to stop growing for about 2 weeks to reestablish their roots.

From now on I think mounds are the answer to planting dahlias at least til I find a better place to plant them.

I live probably 15 mi east of you in Gloucester County, NJ. i leave my tubers in the ground and have 90 - 100 % return. Even with this past horrendous winter where my crepe myrtles & hydrangeas suffered badly, all but 2 of my dahlias came back. My soil here is pretty sandy, but Im sure our temperatures are pretty much the same as yours.

Very cool that you're testing what might work best for you, Highlander!

I'm in Northwestern PA, zone 6, and left several clumps to overwinter of plants that seemed virused, wondering if the cold might eliminate the symptoms. They were sprinkled in three different beds, with different areas of protection (one had a garage to shield the wind, another two were planted 14inches out from a foundation wall with an overhang, others were in the open) . All three beds have never been waterlogged even in the worst torrential downpour. A couple had mounds of mulch to protect them from the worst of the cold. Not one tuber in six different clumps made it.

It would be really nice if that was a reasonable option for me, but I would not risk my whole crop to the whim of the winter. Even in storage, I separate out a few tubers from each variety to store separately, playing the odds that at least some will survive to grow the next season.

For a couple of years a friend of mine did not dig her dahlias, and they all came up here in southern Ohio. So last winter I decided I would try the same. By January it became apparent that this would be an unusual winter. So during a break in the weather in early January, I went out and dug the dahlia tubers. This spring, I started them all in pots. My friend lost 90% of hers. So the lesson is: Dig if you want to be safe.