29 October 2019

Seeking advice re dahlias

I am new to the world of dahlias.  I've been told it should be "in my blood" because my Norwegian grandfather used to dig up his dahlia tubers to store in the root cellar in the winter (probably buried in sawdust or sand) along with carrots and potatoes.

I grew up living not far from the University of Minnesota Landscape Arboretum, which has a section devoted to dahlias (photos above and below).
Each year the Dahlia Society of Minnesota plants a new selection of hybrid dahlias (Dahlia var.) which are then monitored by the Society for growth, habit, disease, flower quality and other guidelines and makes recommendations to The American Dahlia Society. Therefore you will only find numbers and letters on the labels - not names. 
The blossoms are sometimes spectacular:

But the naturalist in me noted that the bees prefer the more basic (?more primitive) flowers -

- rather than the complex ones that the hybridizers prefer.   I've noticed that with other types of garden flowers - convoluted ones probably have less accessible nectar and pollen.

The other thing I noticed about the arboretum dahlias was the impressively robust stems (tip of my trekking pole for size comparison in the photo above).   Clearly these particular specimens are several years old and have had their tubers protected through multiple Minnesota winters.

This year I decided to add dahlias to our garden.  This past spring at our local Farm & Fleet I purchased a couple dahlia tubers.  I didn't think to take any "before" photos, but they were basically small scrawny shriveled things that were totally unimpressive.  I tilled the top couple inches of an unused portion of the garden and stuck them in.  By midsummer I had to add some vertical supports because they were already 3 feet high.  By the end of the summer they were about 5' tall, with fist-sized attractive blossoms.

After the first frost but before the hard freezes to come, it was time this past week to dig up the tubers.  I wound up having to dig a rather deep trench to be able to get under them (and note the plant stems are still rather gracile compared to the old-timers at the arboretum) -

The digging entailed a bit of work, because the plants had sent roots below the topsoil into the clay underneath, and I didn't want to fragment the cluster of tubers while getting them out.

I checked out a couple library books for advice on how to overwinter the specimens.  The first step seems to be to "hang them up to dry", so I've got them sitting in an elevated wire basket on the wall of the garage -

After they dry out a bit I'll clean them up by brushing the dirt off, but won't wash them because moisture increases the risk of mold.  I plan to wrap them in newspaper and keep them in the unheated garage, which in midwinter will get below the recommended 40-50 degree optimal storage temp, but should protect them from the subzero temps that will occur outside.

When spring arrives I apparently will have the choice of subdividing those clusters or replanting them as they are.  I'll probably choose the latter.

I'm posting this partly for family but also to ask readers here for any advice you may have to offer on the management of dahlias.  The books and website I've read offer some variations on how to store and how to replant the tubers; I'd love to hear comments from any readers who have actual hands-on practical experience with these plants.

RelatedFirst prize at Corso Zundert, 2012.

Update:  After the tubers sat on that rack in the garage for a week, the soil around them dried out enough that I was able to brush it off without damaging the tubers themselves:

Now I need to store them in some material that will keep them not-wet, but also not dried-out by the winter air.  Lacking sawdust and sand, my choices are probably clean cat litter, potting mix, or straw.  I'm concerned the cat litter might have desiccant properties.

Update summer 2020:

Mixed success.  Some nice blooms starting to appear -
- but the local rabbits have found the plants quite tasty.  I've lost many of them, despite having fenced in the main dahlia patch (the baby rabbits went under the wire).


  1. It looks like you did pretty well from your pictures. I live in upstate New York. We have had 30 degree nights, but our dahlias are still blooming. I would not expect your bulbs to make it through the winter if your garage gets below freezing. I have a basement that is not kept heated, but does not freeze. For information, I would recommend Swan Island Dahlias of Oregon. Their URL is https://www.dahlias.com
    They have growing instruction and a gorgeous catalog.

    1. Thank you for the link. Our local supply is quite limited, but that catalogue is huge. :-)

  2. You are right that the simple flowers with an accessible area in the centre are better for insects. I keep bees, so I only grow this sort of dahlia. The others might look nice, but they are no good for the bees and butterflies.

    I live in a climate where lifting dahlias isn't necessary, however I have lifted mine a couple of times when either moving house, or moving the dahlias to a different part of the garden. The first time they were stored in plastic bags with sawdust, the second time just loose in cardboard boxes.

    Dividing them is only possible when there is more than one stem. The tubers have to be attached to a stem to re-grow. Tubers which become detached from a stem will just rot away. So in your photo, the one in the centre front doesn't look divisible, but the one on the left could be. The trick is to separate the stems without breaking the tubers off. But it wouldn't hurt to wait another year and divide them when they are bigger.

    Happy dahlia growing!

    1. Thank you for the insights Vireya. I'll plant a couple flat ones next spring and not venture into dividing my old ones just yet.

  3. William Halsted had quite a collection at High Hampton.

  4. I grew up in Minnesota as well and remember digging up dahlias, covering of the roses etc as we prepared the gardens for winter. I am now fortunate to live in France in an area that enjoys maritime climate (Brittany) where I'm learning anew gardening that is for all purposes year round. No more digging up tender perennials!

  5. I live in CT and just lifted my dahlias last week. I store them against a north wall in my cool basement, usually in a big plastic pot and covered with shredded paper, with an inch or so of newspaper on top. I've also stored in sterile potting mix to cover by 3-5 inches. Frost, water and light are the enemies in storage. Check carefully for soft tubers that may have borers or grubs, cut off cleanly and discard these. I've had the same plants going now for 15+ years and they get bigger and better all the time! I do plant loose stalkless tubers in a sort of nursery row and they will often put up a stalk and grow more tubers, tho' some just rot...

    1. Thank you for the tips, unknown person. My clusters dried out nicely in the elevated rack and I was able to gently brush off all the adherent soil. Now I need to pack them in something - lacking sawdust and sand, my choices appear to be potting mix or dry kitty litter (unused). I'm concerned the latter might have desiccant properties, so will probably choose the former.


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