Digging and Storing Dahlias

 Once again we have reached the time of the year when we harvest our Dahlia tubers.  I say harvest not because I am going to eat these, although I could, but because I want to save my root stock for next year.  This is a multi-pronged project, harvest, clean-up and organization challenges all rolled into one.  This year I have about 40 plants and I have different goals for each variety.  One white variety I want to get rid of.  Easy.  I dug it up and threw it in the compost.  Two varieties I want to be sure to increase my numbers.  And most of the others I just want to preserve what I have.  But that includes having one or two spares for backup in case one doesn't store well.  I've written about my dahlia storage methods before, but each year I get a little better at orchestrating the whole process.  I just noticed that I finished this process in 2021 on exactly the same day.  Oct 29th.

There is a certain amount of timing to digging dahlias.  #1 they should be in the ground at least 120 days to create strong enough tubers to survive storage.  I was weeks past that.  #2 they should never be frozen in the ground.  This turns them to mush and is the main reason people in growing zones below 7 have to dig them if they want to preserve them.  One rule of thumb is to wait for a killing frost, leave them in the ground for two weeks to form growth eyes, and dig them before the ground freezes and ruins the tubers.

We have now had a couple of light frosts, but not cold enough to reach the dahlias in the warmer garden areas.  Still, the task you never start takes longest to complete.  My main Dahlia bed was a mass of foliage.  I went in with a lopper and a saw and began picking it apart.  There were also stakes and clips in there that needed to come out.  But still it doesn't take long to disassemble,  As I chopped I saved a bouquet of the nicest blooms.

Once you have the clump carefully uprooted with a fork, you have a couple of options.  You can either set them out to dry like that and simply brush the worst soil chunks off.  In fact, that was how I began years ago.  I would line some cardboard boxes with newspaper, place the dry but dirty tubers in whole, and fill around them with compost.  And that worked fine for the most part.  The downside is that it takes up a lot more storage space and in the spring you have a pile of big ugly, dirty clumps to plant and I didn't really enjoy that.  Single tubers are much easier to plant for several reasons but the main one is that you don't have to dig as big a hole!  If I wanted to replant these in the spring as they are, I would have to dig a hole a foot wide and almost as deep.

The second option involves cleaning them and the fastest way to do that is to blast them with a hose.  This is more work, but you end up with a cleaner product which is more fun to pull out of storage and plant in the spring.  You also reduce you chances of rot because you are removing damp soil and earthworms and getting a better look at the stems and damaged tubers that should be cut out to prevent them from spoiling the whole clump.  Because I want to identify my varieties, I make sure to keep a tag with each clump.

Once you have the tubers washed you have the option to divide now or wait until spring.

This one was really easy.  I just used the two stems to gently pry the clump apart and voila' - two clumps.  I also removed the large, dark "mother tuber".   I could stop there, but this wheel spoke pattern is a little fragile and I would risk breaking some or all of the necks with additional handling.

Dividing clumps is all about getting growth eyes matched up with healthy tubers.  This is the most challenging part and is an acquired skill.  Since I am mostly trying to preserve a specimen of each variety I have, it isn't important for me to maximize the number of tubers I am storing.  My goal is to get one or two nice tubers off of each clump and discard the rest.  I may have as much as 80% waste to get there.

If I divided this up, first I would probably need an oscillating saw just to start on it, and in the end I would have way too many plants next year.  All I need is one or two tubers and the rest can go.

The more you handle a clump, the more chance you have of damaging it.  But most come out of the soil with at least some damage no matter how gentle you are.  Broken necks are the most common.  The weight of the unsupported tuber puts uneccessary stress on the narrow neck. 

Each little white bump on the crown is an eye which will sprout a stem

Not only will that individual tuber not support growth in the spring, but that ragged surface is a great place for moisture and bacteria to enter and cause decomposition.  So the first thing I do is trim off any tubers with broken necks and shorten the stem down to no more than an inch.  I also remove the dark tubers (which indicates that was the original "mother tuber" planted in spring) which will grow, but have a greater risk of rotting over the winter.

The second most likely damage is a broken or speared tuber.  This would probably heal.  But a clean cut will heal better.  I always cut the tail roots off and they will regrow next year but you can cut pretty far into the body of a tuber and still have a viable plant.

Below is an example of a tuber that was blunt cut last year.  The flat end heals over and it grows a tangle of multiple roots.  The two tubers to the right are new with long pointy tail roots.

That cut was a little drastic, but I did it for illustration purposes.    I only really want one plant from this next year so when I saw how far I needed to cut this one, I ended up removing it entirely.

This is all I need

One thing that dividing causes is a bit of a labeling problem.  Below are two clumps from the same variety.  The one at the left is divided down into what I would want to plant next year.  The one on the right is the way it came out of the ground.  The one on the left present more of an identification problem.  But there are solutions for that.

I went ahead and chopped up the one on the right to show you the core that had developed because I had not divided this for a couple of years.  The multiple crowns continue to swell and produce stems and after awhile you get this big ugly knot in the center.

The Big Ugly Knot

Below is one of the salvaged tubers that now needs to be individually labeled.  If you were to wait a few days for the skin to toughen, you could write on it pretty well with a Sharpie or a GardenMarker.  But in this tender, damp stage the best solution is an indelible pencil which has dye in the lead.  When put to a damp, rough surface, the point liquifies and writes beautifully.  These are also used in the dental industry, on watercolor art, drafting etc.  

Besides developing skills of identification and cutting, years of experience leads to a good selection of the right tools.  You want at least a good sharp pair of pruners and a marking pencil.  Below is my kit.

Pruners, Snips, Grafting Knife, Sharpener, Indelible Pencil, Garden Marker, a Nail Brush, some sort of saw blade, Lysol Wipes or bleach solution for disinfecting tools between tubers, and a sorting method.

These cheap utensil trays from WalMart are good for sorting.  It may take several days over the course of a week or more for me to get everything washed, dug and divided.  Before I know exactly how much space I need for final storage, I keep tubers sorted in trays and Sterlite shoe boxes always covered in coarse Vermiculite to keep them from drying too much and shriveling.  A tuber should never be left out in the open air for more than a day or it will lose too much moisture.  As soon as the skin is dry to the touch they need to be in a storage medium which could be sawdust, coir, shredded paper or compost.  I use Vermiculite. Some people even wrap them individually in plastic wrap.

And now, after everything has been divided and individually labeled, I found that this year I could reduce my storage from two crates and a Sterlite tub... and an additional shoe box for Begonias... down to just one Sterlite tub.  Which simplifies things tremendously when I have to move it in or out according to temperature.  The tubers need to be stored between 35F and 50F degrees.  For me that is the bottom of the basement stairs in the bulkhead.  I place a remote sensor for the indoor thermometer on top of the lid and if I am concerned that the temperature may drop too low for the night I will bring them into the basement.  That only happens a few times a winter.  Once a month I will open the tub and remove a few tubers to make sure they are still plump and healthy and not shriveled and dried out.  If they are drying to much you can mist some water on the storage medium.  

Now all of the dahlias are carefully tucked into storage and that is the last gardening chore for the year.

**Footnote:  After completing my inventory I calculated that the tub holds over $1000 worth of tubers if I were to replace them all full price this year.  Of course I always buy at discounted prices.  And my value has multiplied over the years.  One Cafe' Au Lait tuber from 2018 has increased to 18 over the years and I could have three times that many had I divided more carefully.