Storing Dahlia Tubers
Portland Dahlia Society November 12, 2013 Meeting
By Ted  J. Kennedy

The first concept that was discussed was the theory that you want to store a dahlia tuber for the winter in
such a way that it does not have too much or too little moisture. A tuber ready to store should be plump but
dry. And in the Spring at planting time, it should still be plump and dry. And of course, we do not want
tubers to rot in storage.

A discussion of the reasons tubers rot ensued. The obvious culprits were too much moisture and fungus
infections. It was pointed out that broken necks are a big cause. How to avoid broken necks was
demonstrated by some club members. Careful digging was demonstrated.  Other causes of rot were insects
and insect larva. And finally, genetics as many varieties have tendency to rot in storage no matter what you
do.

Some people use powders or dips on their tubers but the consensus was that none of them do much good
with the exception of cinnamon powder. And we are still experimenting with cinnamon.   

It was pointed our that there are several successful ways that our club members store their tubers.  The
most popular method is the use of coarse vermiculite and plastic bags such as grocery bags. About 10 or
fewer tubers, preferably of the same variety are placed into the bag with about 2 cups of coarse
vermiculite.  As Bob Merill commented, he then shakes his bag like he is making a martini.  Anyway, no
water is added and the bag is not sealed but left somewhat loose at the top. Several of the bags are stored
together is some sort of container such as a plastic storage box.  Coarse vermiculite costs about $28.00
per bag at Concentrates.

Eric Toedtli shared his method of storing tubers in Saran wrap. Yes, he specifically uses the classic name
brand only as he says it has some special characteristics that allow the tubers to breathe. He uses about
10-15 rolls to store his tubers from his approximate 600 tubers clumps. He takes about 10 tubers of the
same variety and rolls them into the saran wrap. He first pulls out a two foot long sheet and lays it on the
table. He then proceeds to roll each tuber so that it is covered completely with wrap and then continues with
another until all 10 or so are rolled into a bundle.  He then wraps masking tape around the bundle and
marks the tape with the name of the variety. He says that if a tuber rots it does not generally affect the
other tubers in the bundle although once in awhile a bundle may have more than one rot.  One of the great
advantages to the Saran wrap method is the drastic reduction in storage space.  Since there is no storage
medium like vermiculite or wood shavings the volume of storage space is probably less than half that
needed for other methods.

People who use peat moss extolled it’s virtues but cautioned that premium peat moss that is not overly dry
must be used for success. Peat moss is very acidic and tubers successfully stored in it look pristine. Care
must be used not to use overly dry peat moss, however.

And briefly mentioned was cedar shavings as cedar seems to have  some insect repelling properties and it
does not rot easily when a tuber rots.

Some discussion about how commercial growers store tubers ensued. Swan Island methods and Dan’s
Dahlias methods were discussed.  Swan Island uses tulip crates lined with newspapers and no other
storage medium.  Dan uses similar  plastic crates and uses vermiculite. Both operations have specialized
storage areas.  

Lots of discussion was devoted to the “die-hard” people who refuse to dig their tubers and leave them in
the ground.  One person stated that her neighbor leaves her twenty clumps in the ground and loses about
5 or 6 each year. Another person said that her neighbor had the same tuber clump in the ground for about
20 years and it does well each year. Another club member who grows them on a gentle slope leaves them
in the ground and most of them make it each year. It was pointed out that varieties that make small tubers
may either not make it all or that conversely if they make it the tubers grow much larger. No consensus was
reached as to whether that was good practice for such varieties. For all of those people who leave them in
the ground, it was emphasized that the garden area absolutely must not be overly wet. Stories of dead
dahlias from flooding and wet were told.  

When storing dahlias in the ground some sort of protection from freezing is required. Nearly everybody
uses leaves placed over the cut down plants to protect them from both freezing and too much rain.  Lots of
discussion about the possibility of rot from water accumulating in the hollow stock ensued. Some people
thought it was sufficient to cut the stalk down to where it is no longer hollow while others cover the hollow
talk with plastic cottage cheese containers or aluminum foil. The use of a plastic sheet over the dahlias in
the ground was discussed and no clear guidance was agreed upon as there were advocates and
naysayers. Some thought it promotes rot other thought not.

A short discussion about storing undivided tuber clumps was interesting. Consensus was that you will loose
many tubers to rot as the stem rots and carries rot to the tubers.  Also the clumps will dry out more and be
difficult to divide.  An finally, it was pointed out that clumps that had dried out almost entirely will grow in
most cases. But nobody advocated storing undivided clumps as a best practice.