Wrapping It Up

 Dahlias can simultaneously be both wicked tough and fickle to the point of being delicate. In a nutshell, they are tubers that just happen to make really pretty flowers. If potatoes were as fussy of a tuber, we wouldn't have french fries. I bring up potatoes for two reasons. One: you can eat dahlia tubers. That would be silly and wasteful, but nonetheless true. Two: their storage needs are very similar. Most of us keep potatoes in our house for a week or two before we consume them. If we had to keep the potatoes over the entire winter, then we'd be more aware of the myriad conditions that ensure safe storage. More on that at the end.

Let's start out with discussing digging and cleaning. If you're an expert on dahlias, please feel free to correct any of my observations in the comments. 

When should you dig your dahlias? In my zone 6 (really more of 5b) garden, we usually see a killing frost sometime in October, generally before Halloween. By killing frost, I mean the kind of cold that lasts for a few hours into the early morning. This isn't a dusting of frost on the grass, but rather that sinking cold that takes your lovely basil and turns it black and slimy. With dahlias, a killing frost will stop all the flowers in their tracks and the thick watery stems will die back severely. I wish I had some photos of the destruction after a hard freeze. Once you've seen it, it's obvious. Okay, everything froze, now what?

The first year I grew dahlias, I thought that I should dig them up as soon as I could after they had experienced that killing freeze. Yeah, not so much. Turns out that there are a couple other considerations that come into play. Once the above-ground part of the plant is dead, you can cut it back, nearly to the ground. Compost all those tops. I send my tops through my push mower with a bag on it. The discharge is incredibly wet!  Let's assume you went to the trouble to label your plants (do it! You'll regret it if you don't)... those tags need to accompany the bunch of tubers once they are out of the ground. 

You can apparently leave the tubers in the ground for a considerable amount of time after the above-ground parts are dead and cut away. This is actually really important because the washing and drying steps that occur next are typically happening in October/November. This is usually the wettest, coldest part of the Autumn. Sunny days are in short supply. Knowing that, you can move your digging days around to when it feels good to have bare hands in cold water outside. Yeah, this part is not my favorite. 

 

This year I tried digging out just enough clumps of tubers to fill my planting table (wire fencing over lumber... nothing fancy). This amounted to 5-8 clumps at a time. Sometimes if I was feeling really excited, I might dig up a dozen. Next step involves washing the tubers off with a high pressure stream from the hose... assuming your hose isn't frozen solid. Ask me how I know. 

With the tubers free from dirt and debris, leave them to dry. How dry? How can you tell how dry? This is something I am experimenting with. You want plump tubers for storage. But if they are wet, or still moist when you store them, they will rot. Hideous smell. Once you've smelled that rot in the dead of winter, you won't forget it. I have been trying a couple of different ways to determine dryness. This year I tried a method that came from my days of making pottery. Much like testing greenware for dryness before loading a bisque, you can press the tuber against your cheek or the inside of your arm and feel the temperature. If it is room temperature, or warm... it is dry. If it is cold, it is still wet and needs a little more time. From digging and washing to dividing and wrapping can be a day or two. 

How do you know when they are "too dry"? They get shriveled up. As long as you catch them at that point, they'll be fine. Just don't ignore them and assume you have all the time in the world. 

 

Look that those clumps!

Sometimes I turn the clumps during the day to ensure that everything dries evenly.

Dividing them (now or later?) This is a great question. There are huge sections of books devoted to this topic. You can make your decision based on your own experience. I don't have a guaranteed workflow that is perfect. I have lots of questions... and a few observations.

First observation: finding the "eyes" is an absolute crap shoot when dividing tubers in the fall. I have a theory about why... but not enough time and practice to know if I'm heading in the right direction. My guess is that when you cut down the tops of the plants, the hormones in the tubers flip... and if the ground is still warm (and it usually is in the fall)... then the plant would want to send up new shoots as quick as possible. This would show up as eyes near the neck of the tuber. So far, I haven't seen this occur. My guess is that my ground is already getting cold by the time we see our killing frost. It is also possible that I haven't left the tubers in the ground to cure long enough for them to form eyes. This year we left them in the ground 7-10 days before digging. Still no visible eyes.

Which leads to my next observation: dividing tubers without eyes means you have to be ruthless. An average sized clump might have 10 tubers. Some will be thin and not much bigger than a thickened root. Others will be potato-like. Sometimes the clump will be so convoluted and knotted you'll think there is no way to separate the tubers. Watch some youtube videos. And then be ruthless. 

What does that look like? Absent ruth, it looks like dividing the clump in the middle wherever you can get a pair of pruners into the thickened mass while avoiding the best looking tubers. Yeah, it's easier when someone else does it on Youtube. I struggle. This year I tried a new tool: the cordless oscillating tool. I am brand agnostic. If you like Ryobi or Bosch or whatever, go for it. I don't think the dahlias care. I buy cheap blades by the hundred pack and toss them after a day or two of cutting up tubers. I wipe the blade down with 10% bleach solution in between clumps of tubers.  The oscillating tool I bought was from Dewalt, because I already mortgaged my house to pay for their battery system. 

A pile of cut up tubers, waiting to be wrapped.

Tubers drying and almost ready to wrap up.

Keep your tubers organized. Avoid getting ahead of yourself. Keep the clump together with its ID tag. After I have divided up the clump, I like to set the divided tubers into a plastic flower pot, with the cut end facing up. Why? Well, I have a theory that the cut end needs to callous over before storage. I don't know this to be fact... but I have observed that whenever I have stored freshly divided tubers, there's a higher incidence of rot that happens in storage. So, now I set them aside for a day or just overnight. The next day, I test the tuber for dryness. If they are room temperature, I get ready to wrap them up.

Storage is all about maintaining moisture and humidity until springtime.

We have tried quite a few different ways of storing our tubers. I came across the idea of wrapping tubers in cling film two years ago, and so far, it has produced great results. Probably less than 10% rot of the whole crop. My guess is that is more a result of me rushing to store tubers that weren't completely dry before wrapping in cling film.  Here's the link to the American Dahlia Society's page on using cling film for storage. 

 

By the time we have dug up a few dozen clumps, we end up with a few boxes of cling wrap bundles ready to go into the basement. I typically check on them a few times during the winter. Smell is the clearest indicator, as I mentioned earlier. Rot stinks.

When do I take them out of storage? This is something I dont have enough experience to say anything authoritative about. Usually, about the same time I am getting excited about peas sprouting in the raised beds, and we're eating the first greens (usually chard or kale).... I will start bringing these tubers up into our enclosed porch. It's not as warm as the house, but not as cold at night as being outside. A few days in 40-50F space, and they will start to show shoots on most of the tubers. Once they are showing growth, you can either pot them up into individual plastic pots or you can plant them in flats. It's really up to how you want to plant them out once the weather warms significantly more.  Which begs the question of what the ideal temperature is for setting out the final plants.... and I struggle with this. The best advice I can give so far is to wait a week longer than you think is enough. I know, that doesn't help. But they really want warm soil. They will stop growing if you put them in cold wet soil. With most transplanting, I try to aim to get things planted just ahead of a rainy spell. I do the exact opposite with dahlias. I try to plant ahead of a long dry sunny spell. Once there's substantial plant material above ground, they can manage a deep watering. 

I should probably write a post about staking and supporting dahlias... especially now that we're adding ornamentation to our stakes.