FAQ: Post-Season Questions

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Table of contents
» Do I have to dig up the dahlia tubers?
» I'm in zone 7-10. Do I need to dig my dahlias?
» When should I dig my dahlia tubers?
» I've never dug up tubers before... What should I do?
» What tool do most growers use for digging dahlia clumps?
» How do I divide my clumps?
» Should I divide the clump now or store it whole and divide in spring?
» How do I store my tubers?
» Storing tuber clumps for the winter with dirt attached
» What are these bumps along the side of my tubers? Are they okay?
» Why does this newly dug clump have so many shoots coming up? Is it healthy?
» What is this round lumpy growth on my tuber? Is it okay?
» What question/answers do we need here?

Do I have to dig up the dahlia tubers?
**For readers that think digging/storing dahlia tubers is too difficult or time consuming**
There is no hard and fast rule that says you HAVE to overwinter dahlias inside... there are lots of casual gardeners who treat dahlias like annuals, and that is really okay to do. After all, that means you get to choose new colors/forms every year, and you can get several tubers for the same price as a flat of pansies.

For those in a warmer climate that can successfully overwinter in the ground, be aware that tuber clumps can rot with too much moisture (see other FAQ below) or grow to unmanageable proportions if never lifted and divided.

For those up for a challenge and look forward to climbing the learning curve, digging/storing and dividing your dahlia clumps can provide a wonderful hobby that continues throughout the year.

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I'm in zone 7-10. Do I need to dig my dahlias?
Dahlia tubers go dormant even in the warmer zones, and are susceptible to rot with the winter rains. They can be successfully overwintered in the ground, but you will increase survival rate by cutting the stalk slightly below the surface and covered with a tarp and mulch to avoid pooling of water around tubers when they are completely dormant.

Since they need to be dug and divided regularly to keep the plants vigorous over the years, many serious growers dig/divide every year regardless of climate.

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When should I dig my dahlia tubers?
If possible, wait at least ninety days after planting out before digging, to allow the new tubers to mature so they overwinter better.

Lots of growers wait until a killing frost turns the leaves black, cuts the stalks down to the ground and allows the tubers to sit for 10-14 days before digging. This allows new eyes to form, making it much easier to divide the clumps into individual tubers in the fall.

Other growers in zone 4-7 dig in October, before the killing frost and fall rains. These folks believe that the fall rains can cause the tubers to absorb too much water for good storage, and fall flooding can transmit bacteria/fungus to the tubers, encouraging rotting during storage.

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I've never dug up tubers before... What should I do?
-cut off the dahlia stalk about four inches from the ground
-tag the dahlia stalk with the variety name
-put away any leaky hoses or stakes from the growing season
-wait three to ten days from cutting down, then use a spade to make a circle around the clump, about eight inches around the stalk.
-gently pry with the spade, pulling on the stalk ever so slightly until the clump is free from the ground. Stop if there is any resistance, and use spade to loosen around clump again.
-Remove any dirt with your hand, then take labeled clump to a separate area to hose it down to remove the rest of the dirt.
-allow clump to cure for a week before storage

Click here for an in-depth article dedicated to digging/dividing:

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What tool do most growers use for digging dahlia clumps?
Most growers use either a spade (flat blade with a broad foot push area) or a gardening fork for digging dahlias.

Spade- useful for slicing off ends of tubers around clump before prying out of the ground.
Fork- good in very sandy or loose soil, but be careful of not breaking the tuber's necks when pulling out of the ground!

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How do I divide my clumps?
"It is nearly impossible to teach dividing dahlia clumps unless you do a hands on demonstration. Beginners always cannot see the eyes. It is like a veil was pulled from their eyes when an expert shows them where they are. You will figure it out. If you do not have someone available to show you, dig the tuber clumps, leave the dirt on them and store them until Spring. In the Spring they will sprout and you will be able to divide them with the eyes(now sprouts) attached. But if you do divide in the Spring, the clumps will be dry and seemingly will have turned into wood that is difficult to cut." -Ted

There are several very good detailed YouTube videos showing how to divide. It is definitely recommended to watch a few before attempting yourself.

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Should I divide the clump now or store it whole and divide in spring?
"There are countless methods of storing tubers. Most people divide in the Fall for three reasons: (1) the tubers take up much less room than undivided clumps (2) Clumps dry up in storage and are much harder(physically) to divide. (3) some clumps will rot as the central stem sometimes rots and the rot goes into the tubers. Having said all that, I store many clumps as "extras" and divide some of them in the Spring. I have noticed the yield of usable tubers is a bit lower than otherwise."

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How do I store my tubers?
Storage of dahlia tubers is one of those things that has MANY answers, and the 'right' way is what works for you. Trial and error is the only way to find out what will work in your specific storage location.

Many folks wash, divide and dry their tubers before storing in plastic crates/bins/shoeboxes or cardboard boxes, using material (newspaper, shredded paper, sand, peat moss, vermiculite, wood shavings) to separate each tuber from touching the next. Other folks store the whole clump with or without the dirt left on. The best method? Whatever works for you in YOUR storage area.

Try different methods, making sure there are tubers of each of your varieties in each 'experimental box,' and compare the results in the spring. This will help you choose how you store next year.

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Storing tuber clumps for the winter with dirt attached
Storing whole tuber clumps is just a back up to the dig, wash and divide routine that most of us use. Every method has it's advantages a disadvantages:

Storing tuber clumps for the winter with dirt attached:

(1) It is quicker as all you do is place the labeled clumps into the storage boxes and stack the boxes in the storage area.
(2) The tubers in larger clumps store about the same as other methods, however smaller clumps do not do as well.
(3) You may choose not to ever divide the clump and plant it whole in the Spring. I have done this many times. The next year the tuber clump will be much bigger and this can be an advantage with varieties that make small tubers. However, for varieties that make larger tubers, the second year clump may well be almost too big and heavy to dig and divide.

(1) You need much, much more storage space to store the tubers. Probably 3 to 5 times as much space. And you need lots of boxes. I would require about 100 to store 1000 clumps.
(2) The boxes of clumps are very heavy and hard to move around and sort.
(3) You have no idea of how many tubers you will have after division. This is one of the biggest negatives.
(4) You cannot divide the clumps during the cold weather in the Winter as the water has been shut off and it is just too cold.
(5) The clumps are physically harder to divide as they are dried out quite a bit.
(6) You cannot pull out tubers in the Winter and early Spring to trade or sell but must divide the clumps to do so.
(7) One person mentioned spiders living in undivided clumps. Not a problem here. Also rodents could be problem.

But as a back up method to store what may well be excess inventory, storing whole clumps is a good idea. I ran out of inventory on one variety and pulled out our undivided clumps and filled all the orders. Swan Island uses this method to some extent and they are dividing some varieties in February and March. My recent clumps were pretty dry but certainly not completely dry as when I hosed them off of the the dirt, it took only a bit more time than usual. Dirt comes off in big dry chunks using this method.

One important point. If you wash the tuber clumps before storing, this method will not work. As it has been pointed out, the dirt from the soil seems to preserve and hydrate the tubers and most importantly protect them from fungus disease. Washed tuber clumps dry out, shrivel up, and can rot easily. I have heard several disaster stories of people who washed the clumps before storage. Also, it may well be that in low humidity areas(places that experience cold, dry air in the Winter), that the clumps may need protection from drying out too much.


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What are these bumps along the side of my tubers? Are they okay?
Those bumps are called 'lenticels,' which are basically breathing pores that open when the tuber gets too wet. Other then making it really difficult to write on the tuber, they are harmless.

If they get too large and sponge-like, it is possible that your tuber will rot due to too much time in soggy soil.

From Wikipedia:
"A lenticel is a porous tissue consisting of cells with large intercellular spaces in the periderm of the secondarily thickened organs and the bark of woody stems and roots of dicotyledonous flowering plants. It functions as a pore, providing a pathway for the direct exchange of gases between the internal tissues and atmosphere through the bark, which is otherwise impermeable to gases. The name lenticel, pronounced with an [s], derives from its lenticular (lens-like) shape."

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Why does this newly dug clump have so many shoots coming up? Is it healthy?
The cluster of shoots in one area is typical of Leafy Gall Disease, caused by the bacterium Rhodococcus fascians. The plant will not die but it will produce many thin stems.

Once a plant is infected, there is no cure and the tubers must be discarded to prevent spread of disease. According to research from Oregon State Univ, the bacteria can't survive long in soil without plant matter, but CAN be transmitted via tools to other plants. So sterilize your digging tool after finding one of these clumps to avoid spreading it. The soil will be fine for next year's plants.
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(Commentary and control measures below adopted from http://www.science.oregonstate.edu/bpp/Plant_Clinic/IS IT CR...)

There have been field observations which imply that populations of R. fascians may persist for one or two years in soil in which diseased plants have been growing. R. fascians will also love in water, although this is a passive process as these bacteria have no ability to move on their own. On infected plants, bacteria are primarily limited to the surfaces of the leaves, petioles and stems, although some underlying cells may become infected. There is no evidence that R. fascians can systemically infect plants. The disease is primarily spread by taking cuttings from infected plants, and it is difficult to know if the plants you have are clean, because the bacteria can be present on plants for months before symptoms develop. Plants affected by R. fascians often grow with less vigor, have an abnormally short stature, may produce fewer flowers, and may have less root growth, although this varies with the plant species.

Control measures for the crown gall (Agrobacterium) and leafy gall (Rhodococcus fascians) bacteria:

1. Make every effort to start with clean plants. Do not take cuttings from symptomatic plants or plants in close proximity to diseased plants. Agrobacterium infection can be systemic in some plants, and plants can also harbor R. fascians without showing symptoms.There are also varietal differences in susceptibility to both bacteria; use indexed tissue culture derived plants for those cultivars that appear particularly susceptible.
2. Start with clean planting trays, preferably new. Used ones must be washed free of all organic debris before treating with a disinfectant such as Greenshield, household bleach, or Physan 20.
3. Potting mix or field soil should be pasteurized (60 minutes at 160 F aerated steam) before use.
4. Knives or razor blades should be changed or sterilized between plants during propagation.
5. Keep plants off the greenhouse floor and solid surfaces. Runoff water can disperse the bacteria.
6. Immediately remove and destroy any diseased plants plus any neighboring plants or trays.
Plants can be infected with R. fascians for up to several weeks prior to symptom development, so even though the plants may look healthy, they could be infected. It’s best to toss them out. Clean up and discard all old leaves and other plant debris. Soil can harbor both Agrobacterium and R.fascians.

Water management
Bacteria need water for movement, infection, and multiplication. Minimize the length of time leaves are wet; apply irrigation under conditions where leaves can dry in 1-2 hours. Good ventilation will help.

Click the image for an enlarged view.

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What is this round lumpy growth on my tuber? Is it okay?
Crown Gall

Infection with Agrobacterium tumefaciens bacteria causes swelling of tissue into tumors or galls on stems or roots, but these galls do not differentiate into buds or stems. In contrast, leafy galls are well differentiated into easily recognized plant parts.

See above question about Leafy Gall for preventative measures that work for both Crown and Leafy Gall.

(Above description adopted from http://www.science.oregonstate.edu/bpp/Plant_Clinic/IS IT CR...)

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What question/answers do we need here?
Cutting down
Clump vs individual tubers

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Other FAQ pages that may help you:
» Help! I'm new here... What do I do?
Learn the best places to check out first on this forum!

» Dahlia Basics

This FAQ provides VERY basic info on what a dahlia is and how to tend to them, directing folks to links for more details.

» Pre-Season Questions

Quick answers on how to pre-start tubers, take cuttings, starting from seed, etc.

» Growing Season Questions

Quick answers on planting, watering, dealing with pests, topping and disbudding.

» Hybridizing Dahlias- Basics

Currently open to Cubit Members & Active Members.

» Hybridizing Dahlias- Advanced

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