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Dahlias are sub-tropical flowers indigenous to Mexico and other Central American countries. The secret to successfully growing this plant with its showy blossoms lies underground--in the dahlia tubers. This tutorial will show you possible way to preserve these plants for replanting in the spring.
Dahlia tubers are sometimes referred to as "bulbs," although they are not true bulbs; nor are they "corms"--another term that you will sometimes encounter. Hardy only as far north as USDA... plant hardiness zone 9 (or, at best, 8), in cold climates the tubers must be dug up and stored for winter, much like other tender tubers and bulbs, such as elephant ears and canna bulbs.
Digging Up Dahlias
Knowing the right time to dig up your dahlia tubers isn't hard, because Mother Nature herself lets you know in no uncertain terms. Jack Frost is the messenger Mother Nature sends to tell you that it is time to store dahlia tubers away.
When the first light frosts of autumn arrive, the leaves on your dahlias will turn brown. But do not worry, only the flowers and above-ground vegetation have really been killed. The dahlia tubers are still alive underground--waiting for you to dig them up and store them away until warmer weather returns.
Don't be too hasty about digging them up yet. Frost stimulates the dahlia bulbs to begin setting eyes for next year (similar to the eyes on potatoes ). Upon the arrival of light frost, your bulbs start working on their plan for next year's growth. So hold off on digging until a week or two has passed. The exception to this rule would be if you hear a hard freeze is on the way. A penetrating freeze will damage the bulbs, so in this case, dig them early and hope for the best next year.
Storing Dahlia Tubers
The following pages will show you a method for storing dahlia tubers for winter. Be aware, though, that different gardeners have different methods for storing dahlia tubers. In fact, when you consider all the different variables in the project (the precise temperature at which they are stored, the type of storage medium used, etc.), it's not much of an exaggeration to say that there are as many ways to store these beauties as there are dahlia varieties. Success is not guaranteed with any of these methods, so tweak these instructions as needed, in the spirit of experimentation.
It is important to get it right, since your dahlia tubers will spend a lot of time in winter storage if you are a Northern gardener. In a cold region (such as USDA plant hardiness zone 5), plants generally get frosted in early November. Because they are"summer bulbs," you will not be able to re-plant dahlia tubers for many months, and your dahlia tubers will sleep away a good portion of their lives.
Some gardeners do not fuss with the storage method laid out in this tutorial. They grow their dahlias in pots, then bring the pots into a cool (but not freezing), dry area for the winter. Sometimes the dahlias make it; sometimes they don't. But in this tutorial, you will find a generally accepted outline for how to store dahlia tuber for replanting in the spring.Continue to 2 of 10 below.
02 of 10
Digging Dahlias with PItch Fork, Garden Fork, or Shovel
Contrary to popular belief, pitchforks are more than just props used by cartoonists in portrayals of the devil. Pitchforks are useful in certain digging tasks where the objective is something other than to move dirt around. Digging bulbs or tuberous roots is one such task.
"Pitchfork" is an easily recognizable word, but the tool you see in the picture is called a "garden fork." Its prongs are more heavy-duty than those on hay pitchforks because they are intended to be plunged into... the earth to loosen soil, and so must be able to stand up to rocks.
What's the advantage of using a pitchfork (or garden fork) rather than a shovel or spade for digging dahlia tubers? Some people prefer a pitchfork because it is a bit less intrusive (that is, the total surface area it penetrates is smaller) and therefore gives you more room for error in case you slip up and dig too close. The reality is that digging carefully with a shovel or spade can be just as effective. Regardless of which tool you use for digging dahlia tubers, be careful not to let your digging implement come into contact with the tuberous roots, which are easily damaged
Continue to 3 of 10 below.
- Loosen the soil around the dahlia tubers by thrusting the prongs of the pitchfork into the ground about one foot all around the perimeter of the plant, gingerly prying up the soil as you go.
- Once the soil is sufficiently loosened around the plant, plunge the pitchfork in one more time at such an angle as to access the soil underneath the clump of dahlia tubers. At that point, prying up on the pitchfork should free the tuber from the earth.
- With one hand on the stem and the other scooping the clump of tubers, carefully remove the whole works from the ground. Never just yank the dahlias out of the ground without first loosening the soil, because this risks injuring the dahlia tubers.
- After scooping the clump of dahlia tubers out of the ground, poke around the edges gently with a pencil to knock most of the dirt, feeling for tubers with your free hand.
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What Dahlia Tubers Look Like
The photo shows what dahlia tubers look like, freshly dug out of the garden.
Most of the above-ground vegetation killed by the frost can be trimmed away with pruners, but leave a little bit of the foliage in place for now.Continue to 4 of 10 below.
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Washing Dahlia Bulbs in Preparation for Winter Storage
Gently wash the dirt off your dahlia tubers by swishing them around in a tub of water. (Some people mist the tubers with a garden hose to clean them.) Be very gentle in this operation, because even the slightest puncturing of the skin can introduce pathogens that can cause your dahlia bulbs to rot in storage during the winter.
After the washing is done, it is easier to inspect the dahlia bulbs to see what kind of condition they are in.Continue to 5 of 10 below.
05 of 10
Antifungal Powders: Sulfur Dust
- Inspect your dahlia tubers, and trim away any parts that are rotten, as shown in this picture. In addition to excising any obviously rotten sections, remove the so-called "mother" tuber. In the case of first-year plants, this will be the original tuber that you bought and planted. This older tuber is more likely to rot than the new ones, and such rotting could spread to the others.
- After you have made the excision, allow the clump of dahlia tubers to dry a bit, in hopes that the wound... will callous over.
- Apply an antifungal powder to try to prevent the spread of the rotting. Also apply antifungal powder to any other area of the dahlia tuber that is nicked or cut, or where you detect signs of injury. Sulfur dust is commonly used as an antifungal agent for storing dahlia tubers in winter. Feel free to sprinkle sulfur dust around liberally on tubers. But take proper precautions when sprinkling sulfur dust by wearing long pants and a long-sleeved shirt, a face mask, and gloves.
Some people take disinfecting the tubers a step further by mixing in a bit of bleach to the water used to clean the dahlia tubers during the washing process.
- NOTE: Realistically, there is a good chance that a clump of dahlia tubers such as the one shown in the picture above will not survive the winter in storage, in spite of the removal of the rotten part, adequate drying, and the application of antifungal powder. It's fairly common to lose a few tubers over a long winter of storage.
Note that the clumps of dahlia tubers shown in some of the photos in this tutorial are small and sparse. Two reasons can account for this:
Continue to 6 of 10 below.
- They come from young plants. Older dahlia plants will usually produce bigger clumps.
- They were not given a full summer in which to grow and send nutrients down to the tubers. Planting your dahlias earlier in the season will give them time to produce healthy root systems.
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A Healthy Clump of Dahlia Tubers
In this photo, we see tubers from plants that had all season to grow. Its chances of surviving through the winter storage period are much higher.
Trim off those little side roots on the dahlia tubers now; they serve no further purpose.
The next decision to make is whether to divide or not at this time. When you do divide, ideally each division will have at least one eye. When planted in the spring, only tubers with eyes in will produce new dahlia plants. You may also find, though, that tubers... that seem to show no eye buds will miraculously grow some over the course of the winter storage. Hold off on any final judgment until next growing season.
Some gardeners divide their mature dahlia clumps in fall, before storing them away for winter, as long as they can discern some eyes. But others wait till spring when the eyes on the tubers are easier to spot. Furthermore, if you are dedicated to the proposition that wasting time and energy makes no sense, you may want to wait and see if your dahlia tubers even survive the winter before putting any extra work into them.Continue to 7 of 10 below.
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How to Dry Dahlia Tubers
The next step is drying or "curing" your dahlia tubers in preparation for storing.
Generally, you should dry dahlias for a couple of weeks before storing them away. If temperatures will not be dipping below freezing during that time period, and if no rain is in the forecast, it is fine to dry the dahlia tubers outdoors. In fact, since good air circulation promotes drying, outdoors may be preferable. Whether drying them indoors or outdoors, choose a location where they will not receive... direct sunlight: the idea is to air-dry them, not to cook them.
If you are able, hang your dahlias (perhaps in a mesh bag) during the drying process, so much the better. Hang them upside-down, so that any residual moisture in the stem can drain off.
Once the dahlia tubers are dried, cut the rest of the stem off with your pruners.Continue to 8 of 10 below.
08 of 10
Moisten Peat Moss With a Spray Bottle
Find a box to use for storing your dahlias during the winter. Line the bottom with newspaper, etc. to plug up any cracks. Pour some sphagnum peat moss into the box. Note that some gardeners prefer other storage mediums, such as vermiculite, coarse sand, sawdust or wood shavings.
Moisten the peat moss lightly using a spray bottle if your storage area is so dry that the dahlia tubers might dry out. Lightly moisten the peat moss; you do not want soggy peat moss, which will actually encourage rot.
The... battle you face in winter storage of dahlias is keeping a balance between dry and wet. Err on the side of dry.Continue to 9 of 10 below.
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Storing Dahlia Tubers in Peat Moss, Dusting Tips
- If you have divided your dahlia tubers, lay them down on the moistened layer of peat moss and make sure they are not touching (if one succumbs to fungus, there is no point in having it spread to the others).
- Cover the dahlia tubers with another layer of peat moss.
- Store the box in a dark spot that will remain cool for the winter but will not freeze. For many, this means an unheated basement or cellar.
Finding a place to store dahlias at a suitable temperature can be problematic. The optimal storage... area will have a consistent temperature above freezing but below 50°F. throughout the winter. If you simply don't have this kind of storage area, it may be best to treat dahlias as annuals, buying new tubers each year.
Even if you think you have done everything correctly, Mother Nature can intervene and rob you of success. An unusually warm fall, for example, can keep your storage area warmer than it should be, causing you to lose all your stored tubers. So don't be too discouraged if events beyond your control foil your efforts. It occasionally happens to the best of gardeners.
Other Tips for Dahlia Storage
Be prepared to experiment a little with these various methods until you hit upon the method that works best for you.
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- Some people wrap their dahlia tubers in the newspaper before storing them in the box filled with peat moss. Others store them in paper bags.
- Here is a way to facilitate the disinfecting process. Insert some peat moss in a Ziploc bag, and place the cured tubers in the same bag. Follow this up with a liberal sprinkling of sulfur dust. Seal the bag. Gently shake the bag around. (The key word is "gently": you want to move the sulfur dust around, not the tubers.) Remove the tubers gently from the Ziploc bag. They are now ready to be stored in the box filled with peat moss.
- Label the dahlia tubers so that you will know what specific cultivars you are working with when next spring rolls around. If you have lots of clumps to store away, consider using separate boxes, or make sure to properly label each clump.
- Periodically check the dahlia tubers during the winter. If they seem overly dry, spritz the peat moss again with the spray bottle. If on the other hand, a dahlia tuber feels mushy when you check it, it has rotted and should be discarded.
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When to Plant Dahlia Bulbs
Regardless of whether you live in zone 5, zone 6 or zone 7, there is a simple way to remember when to plant dahlia bulbs: plant after danger of frost has passed in your area. If you do not know when that is in your region, ask an experienced gardener or check with your local county extension or a good garden center. In zone 5, for example, you might take the appearance of Memorial Day decoration as your cue to plant dahlias.
Other popular tender plants traditionally installed at the same time as... dahlias include: