FAQ: Pre-Season Questions

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Table of contents
» How to start dahlia tubers
» How early should I start my dahlias before planting?
» How do you prestart tubers before planting?
» Tuber size- the long and short of it
» My tubers are shriveled up and are very light. Should I soak them?
» My stored dahlias start sprouting with 2 inch shoots, and it's January! Help!
» Why is it taking so long for a shoot to develop/ for a cutting to root?
» How can I start dahlias by seeds?
» How can I make cuttings?
» Getting more tubers from poor tuber varieties
» What are pot roots, and how do I make them?
» What are leaf cuttings, and how do you do them?
» Should I use rooting compound to help cuttings root?

How to start dahlia tubers
Here are your options for how/when to start your dahlia tubers:

1. Wait until the last hard frost in the spring, and plant directly into the ground or pot. (go to 'Growing Season FAQ here... http://cubits.org/Dahlias/faqs/view/growingseasonquestio/)

2. Prestart them inside pots 2-3 weeks prior to planting out time, with just-moistened potting mix (very little water until roots are formed and sprouts are up). This method does not need indoor plant lights or greenhouse.

3. Prestart them in pots 1-4 months prior to planting out time, on shelves with indoor plant lights. Just understand that you will have to potentially commit significant time to the maintenance of any plants prestarted, along with potential pest issues that occurs. This allows you to take cuttings for additional plants or pot roots from your existing stock.

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How early should I start my dahlias before planting?
Here is a general guideline for starting dahlias in the spring, from seed, tuber or cutting:

Seeds- 5-6 weeks prior to planting
Tubers for cuttings- 8-10 weeks prior to planting
Take cuttings- 6-8 weeks prior to planting
Tubers for plants- 4-6 weeks for most varieties, 6-8 for giant varieties

Planting differs depending on your location, but a good rule of thumb is when you would plant tomatoes... When the ground is warm, and the last frost is behind you. Too early will set back the plants even without the frost, as they won't continue root growth in cold soil.

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How do you prestart tubers before planting?
Dahlia tubers need two things to sprout and root:
1. small amount of moisture (too much, and they rot!)
2. between 65 degrees to 80 degrees temperature (room temperature works just fine!)

There are three ways growers pre-start dahlia tubers:
1. place them individually or in pairs in a pot with potting mix
2. place 10-40 in a tray with potting mix
3. place them individually or in pairs in a sealed plastic bag with a damp cotton ball or potting mix until sprouting/rooting (requires frequent checking)

Would you like to hear more about these methods directly from the growers? Find their comments on pre-starting tubers here:

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Tuber size- the long and short of it
Typically, most experienced growers prefer the smaller tubers the size of an adult's thumb, where novices prefer the huge tubers thinking the resulting plant will be better. The plant's performance is not linked to the tuber size, but the next season's tuber crop IS linked to size.

Grapefruit-shaped or huge long tubers typically will not produce good tubers the next season, as the plant grown from such a tuber sees no need to build up additional starch (food) stores.

Most experienced dahlia growers chop long tubers 'down to size' without a second thought. Be sure to use a sharp clean knife (disinfecting between uses avoids bacteria and virus spreading), and leave the tuber end to air dry for a day or two before potting up. Some dip the cut end in cinnamon or garden sulfur to aid in the curing process. When dry to the touch, plant as normal.

This vendor just snapped off the end, not using anything for the end. He probably didn't let the end dry before storing in vermiculite, as there are root hairs from the moisture on both of the tuber tails. This serves to show that a cut tuber will indeed root from the sides, not just the very end of a dahlia tuber.

Thumbnail by CCvacation
Click the image for an enlarged view.

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My tubers are shriveled up and are very light. Should I soak them?
If they are really light, most likely they are goners. But you can always pot them up with just-damp potting mix and see if they sprout in a few weeks. You'll know then if they have any life left in them. Very little moisture will set the tuber's growth in motion, if there is any life in it.

Water often starts rot. It doesn't make sense to soak tubers in water, as their fine feeder roots are destroyed when originally dug from the ground... they can't drink water without them. Too much water will water-log the tuber and reduce its chances for survival. The dead tissue of the outer tuber will soak up excess water like a sponge, and that is not a good thing.

If you have a lot of dried up tubers, you might try throwing them all in one pot with some just-dampened soil above and below (cool to the touch, NOT dripping or soaked through), and let it sit for several weeks. Then, excavate it carefully, and see if there are any shoots. Repot those living tubers into single pots, and be very conservative in the amount of water you give it... just enough that the soil is cool to the touch, not wet, until there are leaves spreading out. By then, feeder roots are established, and the tuber can handle more water, as long as there is adequate drainage.

Again, very little moisture will set the tuber's growth in motion. Give your 'goners' a chance... they might surprise you!

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My stored dahlias start sprouting with 2 inch shoots, and it's January! Help!
You can leave them and the shoots will shrivel up eventually, nip them off and toss the sprout, or nip them off and pot the sprouts up. (Just remember that it is a loooong time to have a cutting under lights before it can be planted out!)

Often sprouting is simply that the air has humidity/warmth that triggered the growth response in the dormant tubers. However, sometimes sprouting is an indication that the tuber is rotting. If the ends and sides don't 'squish' with strong finger pressure, you are good.

Early sprouting normally does no damage to the tuber, and it will sprout again once planted in late spring.

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Why is it taking so long for a shoot to develop/ for a cutting to root?
Especially with the giant/large dahlia varieties, the first shoots tend to be wider at the base, sometimes hollow, and take twice as long to get to cutting size then the smaller varieties. When cut, these thicker cuttings take an extra week or two to root, as well.

The solution is to either have lots of patience, OR slice the top off the nub of a large sprout so smaller sprouts form from the base of the nub. This will speed up production time on the larger varieties, allowing the resulting plants to mature quicker and start blooming earlier in the season.

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How can I start dahlias by seeds?
There are two ways to start dahlia from seed:
1. Use potting soil products as a sprouting medium and allow the seedlings to reach a true leaf stage before transplanting into an individual pot
2. "Germinate" the seed to show a slight white sprout and immediately pluck the seed from a medium such as a dampened paper towel and place the seed into a pot.

Read more about both of these methods in the comments here:

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How can I make cuttings?
First, you might be asking "what is a cutting?" It is the process of starting a new independent plant from a sprouting tuber. This is a great way to inexpensively gain more dahlia plants for your garden.

1. CUT- Growers normally allow three leave sets to form on a sprout, and severe it right above the tuber surface.
2. INSERT- The severed sprout is then inserted in a growing medium below at least one leaf set (with the bottom leaves stripped off) to allow roots to form. Growers use a wide range of growing mediums, such as germination mix, perlite, sand, oasis, etc.
4. HUMIDITY- Most growers keep the cutting misted or covered by plastic to keep the humidity high while the cutting develops roots. Some cut the leaves in half or two-thirds to avoid moisture loss.
5. FERTILIZE- Some growers use a very diluted fertilizer at this stage, but most prefer to avoid any fertilizer until roots have formed and there is obvious growth on the new plant.
6. TRANSPLANT- When roots are obvious through the weep holes on the bottom, and the cutting has obviously grown (average of ten to fifteen days), carefully transplant cutting to a four inch pot until planting time.

For a more in-depth look at one hybridizer's method, check out this article titled, 'The Beginner’s Guide to Dahlia Cuttings,' located at this article page:

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Getting more tubers from poor tuber varieties
How to get more tubers from a variety that produces very few tubers:

I have noticed over the years that there are two categories of dahlias that are lousy tuber producers. The first and worst are the "rotters" that may make some nice looking tubers but when you try to store them for the Winter, they rot badly and you end up with very few or none. Other than taking cuttings and turning several into pot tubers, I know of no method to store them. These varieties are genetically prone to rot from fungus infections and nearly all of us have the type of fungus in our gardens that infects them. Even a percentage of the pot tubers will rot.

The second category are the varieties that just do not make very many tubers. If there is a tuber or two , they store well but you want more than just one tuber from the plant. I have found that if you do not divide the clump(if you can call it a clump) and plant the entire clump the next season, that you will generally be rewarded with about 5 or 6 nice tubers and sometimes more. This method also works with varieties that make very small tubers. The second year clump with have lots of larger tubers. And this works too well for varieties that already make lots of good sized tubers. A second year clump from a good tuber maker can weigh over 20 pounds and is seriously difficult to divide.


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What are pot roots, and how do I make them?
A potroot is created by placing a cutting into a 3 inch to 8 inch pot, and growing the plant in that container all season. The container restricts growth of the clump, and results in a potroot that typically stores well and produces many cuttings the following season.

Some growers recommend minimal fertilizer and watering for potroots intended as 'tuber insurance,' but if the pot is sunk into the ground and treated like a regular show plant, the resulting plant will look no different then a regular 'tuber' plant grown directly in the ground.

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What are leaf cuttings, and how do you do them?
This is an advanced subject and if you have not done traditional cuttings from tubers successfully, it is not recommended to try to do leaf cuttings. However, once you have mastered traditional cuttings from tubers, leaf cuttings can help increase your stock when you have very little to start from.

Check out this in-depth article on the topic:

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Should I use rooting compound to help cuttings root?
Dahlia cuttings root very easily on their own as long as you have a leaf node in moist soil and provide enough humidity (70-80%) via a plastic covering of some sort over top the pot with the cutting. It is good to have at least one leaf node (or top of sprout) uncovered from soil where new sprouts can form.

Rooting compounds are best used on softwood & hardwood cuttings, but dahlias have no need for such assistance.

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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.

» Growing Season Questions

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

» Post-Season Questions

Quick answers on digging, dividing and storing dahlia tubers

» Hybridizing Dahlias- Basics

Currently open to Cubit Members & Active Members.

» Hybridizing Dahlias- Advanced

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