How To Plant Dahlia Tubers: The Steps

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Dahlias are an incredibly varied plant, which is perhaps why they’re among the most beloved.

The size and shape of a dahlia bloom can range from a simple Dahlia flower only a few inches wide to the massive dinner plate dahlias, which rival sunflowers for size, depending on the dahlia varieties.

Planting Dahlia TubersPin

You will also discover a huge range of colors and forms available in Dahlia varieties.

But one of the great things about dahlias is that they’re a tuberous plant, which makes it a snap to overwinter and replant them – once you know the process.

Today we’re going to take a look at how to properly overwinter and plant your dahlia tubers so that you get great results every year.

How To Plant Dahlia Tubers

Planting dahlia tubers is a simple process, but you need to do a little planning ahead for the best results.

Let’s look at the various circumstances and related methods for planting that you will encounter.

WARNING: Tubers and Bulbs are NOT the Same!

There is a common mistake that a lot of growers make, which greatly affects your chances of successfully planting anything beyond seeds.

This comes down to there being four major kinds of the root system (bulbs, corms, rhizomes, and tubers), each of which has its own planting requirements.

Dahlias grow from tubers, which are swollen roots used to store nutrients.

The most famous tubers are potatoes and yams.

Like a potato, dahlia tubers can form eyes that develop into shoots, allowing a single tuber to create multiple shoots above ground.

You can divide a tuber into sections containing one or more eyes, and each will result in its own plant.

Bulbs are very different. Onions are bulbs; if you allow one to sprout, you’ll notice that the sprout always comes from the top of the bulb.

You can only plant bulbs in one direction, and the depth must generally be calculated to the top is a specific depth from the surface.

We won’t get into corms or rhizomes here, but they also have unique quirks and planting requirements.

Thus, if you hear someone talking about Dahlia bulbs, be careful not to forget these aren’t bulbs at all and must be handled differently.

Overwintering Dahlia Tubers

When the first frost strikes, it’s time to uproot any existing dahlias and overwinter their tubers.

A heavy frost will kill your Dahlia plant, so it’s best to overwinter them.

Remember, dahlias are reliably winter hardy in USDA hardiness zones 8 and higher.

Once the Dahlia foliage has turned black, cut it back to 6” inches above ground level, then carefully dig up the tubers.

Rinse or gently brush all the dirt away and examine the tubers for any signs of rot or disease.

Common signs of rot include bark brown to black flesh, soft spots or sliminess, or a foul odor.

In some cases, you can treat root rot on your dahlia tubers, but sometimes it’s necessary to remove individual tubers completely or even discard the entire plant if more than ⅔ of the root structure is infected.

You might also discover some sections of the tuber have already broken off of the main plant, which just means the plant’s begun the dividing process for you.

If any of these tubers appear wrinkled or otherwise shriveled, they are likely, not viable and can be tossed.

Once the tubers are clean, healthy, and divided (if you choose to do so), label them so you don’t get different cultivars or plants mixed up.

Allow the tubers to dry out for a week or two, and prepare them for storage.

Paper products such as cardboard boxes or paper bags are useful if the storage spot is slightly humid, as these will help keep moisture away from the tubers.

Plastic is the preferred storage container when the overwintering spot is nice and dry.

Wrap the tubers in some newspaper and place them in your chosen container somewhere cool and dry but not freezing.

Check the tubers every few weeks to ensure they aren’t becoming too dehydrated (a little spritz with a spray bottle is more than enough if the tuners are beginning to shrink) or becoming infested or infected.

Also, you can add compost to your dahlia in late winter.

To Pot or Not to Pot

That is invariably the question that must be answered when you pull your Dahlia tubers out of storage.

When you get tubers in the mail (say, from Michigan Bulb or an online seller), you have two options: to plant in a pot or your garden.

But when pulling tubers out of winter storage, you also have the option of starting off the Dahlia plants early in a pot, then transplanting them outdoors.

So what is the best option for your situation?

Planting outdoors should happen when the risk of frost has passed and when it’s not too rainy.

For most zones, this is between April and May, although if you’re living in especially warm zones, you may be able to plant as early as March.

The real secret is to check the ground temperature, NOT the air temperature.

For dahlias to grow properly, the ground needs to be at least 60° degrees Fahrenheit.

If you want your dahlias to bloom more quickly, start them off 4 weeks before the predicted final frost.

As mentioned, planting time for dahlias in pots can happen as soon as 4 weeks prior to the predicted final frost.

However, you won’t need to store potted tubers during winter, so the only time you’ll need to uproot or repot container dahlias is to divide or change out the soil in the spring.

Planting Dahlia Tubers in Containers

March is usually the best time for planting dahlia tubers in pots or containers and repotting.

The container should be at least 12” inches across and 15” inches deep to accommodate the root system if you plan to keep dahlias in a container.

If planting pieces of tuber, each piece must have at least one active eye and node.

Use quality, well-draining potting soil or a homemade soil-free mix.

Lightly moisten the soil, then plant the tubers or pieces.

For full tubers, plant them eye-up with 3” to 4” inches of soil covering them.

Tuber pieces will only need about 1” to 2” inches of soil on top of them. And should also be planted eye-up.

Water the container and palace in a warm, sunny spot.

Remember that potted dahlias require more regular watering as they dry out more quickly throughout the growing season.

If you are planning to transplant the dahlia outdoors, DO NOT fertilize the potting soil to help reduce the amount of transplant shock the Healthy dahlia will face.

You will also want to begin hardening the plant over the final week before transplanting so that there’s less shock.

Planting Dahlia Tubers in the Garden

The first thing you need to consider is the climate. If you live in a hot climate, remember to find a spot where your dahlia plants will have morning sun and afternoon shade.

They can also be planted in full sun, with about 6 to 8 hours of direct sunlight.

Also, check the ground temperature regularly once the chance of frost has passed.

Once the ground temperature reaches 60° degrees Fahrenheit, you’re almost ready to plant the tubers – but not quite.

Instead, you must first prepare the soil. You can use fertile, well-drained soil, but it may also grow in heavy soil types. 

Till or loosen the soil where you intend to plant the dahlias and thoroughly mix in some organic compost.

Enriching the soil with compost or organic matter, such as peat moss, decomposed leaf mold, and pine bark, will also help increase the chances of success. 

Cow manure or aged manure will also be a good soil amendment.

You can also mix in a bit of organic fertilizer before planting to give your dahlias a little nitrogen. Using an all-purpose granular fertilizer will also help.

Dig a hole approximately 3” to 4“ inches deeper than the height of your tuber.

Look for an active eye on the tuber, which will signal where its crown is.

The eye must face upwards when planting.

The tubers will also need to be spaced properly, with about 12” to 30” inches of space between plants, depending upon the species or cultivar.

Sit your tuber in its hole, then gently add a bit of soil around the base to hold it upright.

Continue slowly backfilling, and if you’re planting a taller dahlia, add in a stake or other support besides the tuber as you fill the hole so you won’t accidentally damage the root system later.

Also, remember to cover the tubers with soil.

When the hole is filled, gently firm the soil surface and give the ground one good watering. Don’t regularly water tubers because too much water can lead to rot at this stage. 

Avoid adding new water or fertilizer until you see sprouts, as dahlia tubers have a bit of a reputation for rotting easily, especially if there’s excessive water before the plant is established.

You should see sprouts within a few weeks.

Once the Beautiful dahlia plant reaches 8” to 12” inches tall and has at least 3 pairs of leaves, pinch off the branches to encourage fuller growth and a bushier plant.

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