All About Dahlias

One of the most sought after flowers from color, varieties, breeders, hybridizers, seeds, tubers--they are all the craze. So while we're here in mid-summer, I thought it would be a good time to talk about these beauties as they are just starting to bloom here in Knoxville TN (zone 7a). We're about to go in depth with everything dahlias starting with the tubers, then the flowers, and then back to the tubers. So buckle up!

If you want to skip around, here's what we'll be talking about:

1. Tuber Anatomy

2. Planting

3. Support

4. Growing care

5. Pinching

6. Harvesting

7. Digging up tubers

8. Storing dahlia tubers

9. Dividing tubers

10. Pests and Disease

11. My favorite varieties I can't live without.

    
    

Let's go!

1. Tuber Anatomy

While dahlias can be grown from seed, tubers are what will guarantee the variety of flower you purchased. For every one tuber you plant, you will grow one plant. The tuber you planted (now considered the Mother Tuber) will multiply under the surface and you will be left with multiple new tubers that can be divided and grown into new plants the following year.

Dahlia Tuber Anatomy

Each tuber is made up of 4 parts and can not grow a plant without them. They include: the eye, crown, neck and body.

• The eye is where the plant grows from. It looks like a little pinkish bud that pops out of the crown of the tuber.

• The crown is what is connected to the stock of the plant when you dig it up.

• The neck is the part that connects the crown to the body.

• The body is the part where the nutrients are held and from which roots grow.

Tubers come in all shapes and sizes. Some have really fat bodies with no necks and some have really long, skinny necks and tiny crowns. The size and shape of tuber does not indicate better or poorer growth, flower production, storage, etc. It's also VERY difficult to determine what variety of dahlia you have based on tuber alone. So it's VERY IMPORTANT to label your tubers!

2. Planting

When planting your tubers, it's best to plant ones that have an obvious eye. This will ensure it's not a dud tuber and increase the chances of having a plant grow from the tuber.

1. Dig a hole 4-6" deep and space your tubers 9-12" apart.

2. Plant your tubers eye up, body horizontal to the ground.

3. Cover it back up

4. Label your plantings whether this is in a notebook writing down who was planted where or adding labels in the ground. I promise you won’t remember in 5 months what you did this spring when you need to dig them up again. And if your dahlias get hit with a hard frost before you could dig them up, the blooms will all look the same—brown!

Where to plant dahlias

-        Dahlias grow best in full sun (6+ hours) in well-draining soil. Being a tuber, they are at risk for rot if left in soggy conditions.

-        Will they grow in clay soil? Yes. Will they grow in containers? Yes. Will they grow in raised beds? Yes. Do they grow better in one vs the other? It depends. Each gardener will tell you differently depending on their growing zone, how much rain they receive, humidity, etc. Some people have great success growing in 5 gallon grow bags. Some people can grow them in the landscape and they’ve been growing in the same spot for years. Some people have such terrible soil, raised beds are the answer.

-        For me, I have the most success in raised beds. I’m able to grow in containers, but the plants are generally smaller and honestly, I forget to water them as often as I should.

When to plant dahlias

-        After fear of frost has passed is the best time to plant your dahlia tubers. Tubers will rot if frozen, so I like to plant mine mid-late April here in Zone 7a. I’ve found June planted tubers generally don’t grow very well, so I won’t plant any later than mid-May.

3.     Support

• Dahlia height will vary based on variety. Most dahlias you purchase from the hardware store will be a landscape variety and grow maybe a foot tall. Diva, Cornel Bronze, Bloomquist York were 3 of the varieties I grow that can be a good 5-6’ tall. Others like Critchon Honey are more of a bush variety, meaning it will grow around 2-3’ tall.

• All dahlias need some sort of support because if left to their own devices, they will grow any which way and you will end up with wonky stems or dahlias growing along the ground.

• The way in which you grow your dahlias will help determine how you choose to support your plants. It will differ if you’re growing your dahlias in straight rows, clumped together in raised beds or dotted throughout the landscape or in containers. Some of the methods include:

  • Staking each individual plant – whether using a T-post, U-post, stick or metal stake, it’s best to place the stake in the ground at the time of planting. This way you’re not risking stabbing your dahlia tuber and killing the plant trying to stake it after your dahlia is already growing and established. This is a great option for container dahlias or ones that are dotted around the garden.

  • Corralling – This usually entails T-posts and either twine/rope or some sort of paneling surrounding your dahlias. I use this method around all of my garden beds (mostly to keep the toddlers and bunnies out). U-posts at the corners and every 4’ along the outside of my raised beds and 16-guage Welded Rabbit Fencing tied and stapled around the outside.

  • Florida Weave Method—Using T-posts and twine, this begins when the plants are small and continues throughout their growth. It works best for plants grown in rows (you may see it with tomatoes, peppers, etc). Using T-posts at each end of the row, tie your twine to one end and weave left around the first plant, right around the second and continue weaving in and out until you read the end and tie to or wrap around the T-post and head back weaving the opposite direction around the plants. You would add a new set of twine weaving in and out every 6-12” depending on how tall the plants get or how much support they need.

  • Netting—Using something like Hortonova Netting that has 6” square openings, this would be placed horizontally over top of the plants and they would grow through the netting. You may need more than one layer depending on how tall the plants tend to get. The netting would be attached to posts around the outside of the plants and pulled taught so birds don’t get caught in it and to keep the plants from pulling it one way or the other while they grow through the netting.

    
    

4.     Growing Care

• Watering- It is advised to not water dahlias until you see growth popping through the surface of the soil to avoid rotting tubers. That being said, I’m always a fan of planting before it rains so I don’t have to worry about watering 😊 So don’t stress either way if it rains on the freshly planted tubers or it’s going to be super dry and you want to give them a little water after planting to get them going.

  • Throughout the growing season, I like to water a couple times a week unless it’s going to be very hot and dry, then I try and push to every other day watering. It’s better to water for a longer period of time, less frequently than for a short period of time more often. This encourages the roots to grow longer in search for more water and give the plants a stronger foundation under the ground.

  • Using drip line vs. overhead watering – one isn’t better than the other. Consistency of time of day the garden is getting watered is more important than the method used. It’s better to water outside of the heat of the day (in the morning or evening, not noon) to offer your plants the best chance for soaking up the water and using it vs. it evaporating from the heat of the day and not fully soaking into the soil.

    
    

• Fertilizing- I always start my gardens off with new compost and Espoma Plant-tone before planting. Throughout the growing season, I try and fertilize my plants monthly. When looking at your choice of fertilizer, you will find a NPK ratio that will indicate how much Nitrogen, Phosphorus and Potassium is included in the mixture. In general,

  • Nitrogen is for green growth (that’s why plants look so green after it rains because rain water contains more atmospheric nitrogen than ground water)

  • Phosphorus is for root development and bloom/fruit formation

  • Potassium is for overall plant health helping fight disease and transport water and nutrients to the rest of the plant.

There is such thing as too much of a good thing. Depending on where your plant is in its growth, I generally start with a higher nitrogen fertilizer like Miracle Gro and then while the dahlias are in bloom, I’ll use a fertilizer with a higher Phosphorus ratio to encourage blooms. I’ve definitely used the same Miracle Gro all season long, so don’t feel like you have buy different fertilizers all season long unless you want to.

**Note: any Master Gardener you speak to will recommend soil testing before planting to see what exactly your soil is lacking and what to use to fix it. You can submit soil samples to your local extension office (in Knoxville, it will be at the University of Tennessee) and get a more accurate description of your soil’s needs including macro and micro nutrients than the home kits which generally only measure macronutrients (NPK) and pH.

• Airflow – this is important for growing healthy plants and preventing the spread of disease. As your dahlias get larger, it’s recommended to strip the bottom 6-12” of leaves from the plants to offer airflow around the lower part of the plant to reduce things like powdery mildew in the high humidity of late summer.

  
  

• Labeling—I’ll say it again. LABEL. YOUR. PLANTS. I like to take a roll of landscape tape and write the dahlia variety with a sharpie on the tape and wrap it around the main stock of the dahlia plant. Sometimes plants are mislabeled or the ones you put in the ground at planting have faded or misplaced. Some of the tubers you originally planted may have rotted and you didn’t know about it until everything starts blooming. However you choose to document, especially if you want to store each individual variety, if you want to sell the tubers or grow more of one type, accurate labeling is necessary.  

  
  

5.     Pinching

Pinching is a technique used for many cut-and-come again flowers that encourages side branching and more blooms throughout the growing season. For dahlias, pinching encourages side shoots to grow long, thin but sturdy stems perfect for bouquets and more blooms per plant. Win-win!

• I like to wait until there are at least 4-5 sets of true leaves before pinching my plants or if I see a bud starting to grow in the center stalk, I know it’s time to pinch.

• To pinch, you will remove the center growing stalk above a set of leaves by pinching with your fingers or cutting with a pair of snips.

**Note: pinching will DELAY flowering. The plant’s goal is to produce flowers to reproduce (i.e. make seeds). When we pinch the center stalk, the plant is now forced to put its energy into growing more opportunities to reproduce (i.e. flowers for bees to pollinate). If it can no longer grow up, it will grow out! This is the branching we want!

Why pinching?

Arrows indicate sets of leaves and where new growth/branching will occur.

Pinching the center growth above a set of leaves.

Pinch with your fingers or use a pair of snips.

Ta-da!

Showing the hollow stem of a dahlia pinched too late. Water can build up in the stock and cause rot.

1.     Have you ever looked closely at a dahlia tuber’s center stalk? Some of these plants can have center stalks the size of broomsticks (American Dawn and Sweet Sanne, I’m lookin’ at you!) If I want flowers for bouquets, I don’t want a huge broomstick of a stem to fill up the entire vase with one flower on the end. I want thin, sturdy stems so I can fit many flowers into a vase to create a bouquet.

2.     Going back to the center stalk of a dahlia—they  are actually hollow! This is why it’s important to pinch while the plant is young instead of allowing the center stalk to bloom and use that for your cut-flowers. If that happens, and the center stalk is too big to heal over, you will now have a hollow tube that will fill up with rain water and drain straight to the tuber and – you guessed it—rot the tuber.

6.     Harvesting

Ivanetti

Your dahlias are ready to harvest when the flowers are fully opened and the outer petals are not shriveled or discolored. This will look different for different types of dahlia. For example, all of the outer petals will be open and point down towards the stem for your ball, decorative and anemone varieties (think Cornel series, Diva, Totally Tangerine). For

waterlily varieties (like My Forever) the outer petals will be open and flat, parallel to the ground.

• I always try and cut above a set of leaves to encourage branching and more stems from that set of leaves.

• Want long stems? You must cut long stems. This may mean sacrificing side buds and I promise, it will be ok! The longer you cut your stems, the longer the consecutive stems will be. You’re essentially pinching the plant back every time you cut stems, so take advantage and make them long!

  
  

7.     Digging up tubers

The end of the season has arrived and it’s time to dig up your tubers. Some growers recommend waiting to dig them after the first hard frost. Some will dig them sooner—really, it’s what works best for your schedule. I promise you farmers who grow thousands

of dahlias aren’t waiting until frost to start digging.

• If you are able to plan when to dig up your tubers, it’s ideal that the soil is dry for doing so. Try and remember NOT to water your dahlias before digging them up!

• Using a broad fork is ideal, but any sort of digging instrument will work. Loosen the soil around the tuber clump trying to give yourself space so you don’t stab the tubers.

• I like to leave the entire plant and stock attached when I pull out my tubers. It’s easier to pull from a long stem than a stubby one. Once the soil is loosened, gently pull out the tuber clump. If there’s any resistance, loosen the soil more. Sometimes the tubers are very long and will snap off the clump.

• Tap the stock on something hard like the side of the raised bed or fence post to remove most of the dirt.

• Once your plants are grouped how you want them and labeled, you can remove the main stock from the clump.

• At this point, you can choose to wash the tubers by spraying them down with water and letting them air dry for a couple hours (out of direct sunlight) or brush off the excess dirt leaving a thin layer of dirt on them. Next step is storage.

Note whether you choose to overwinter your dahlias in the ground over winter or not, you will have to dig them up in the spring to divide them. If you choose to overwinter your tubers in the ground, I would recommend cutting the stock to the ground.

8.     Storing dahlia tubers

**Note you do not HAVE to dig up your dahlia tubers. Some gardeners are in a growing zone where the soil won’t freeze so it’s not necessary. Some gardeners are able to heavily mulch their tubers and store them in the ground instead of trying to find space inside. 

At this point, your tuber clumps are labeled, washed or clean-ish and ready for storage. You can choose to divide your tubers now in the fall or store them in clumps and divide in the spring. Regardless of dividing them now or later, the tubers will need to be stored.

Label

I can not stress this enough. All these potatoes look the same after a long winter. If you think you’ll remember, I promise you won’t! I like to label each tuber with a permanent marker writing the name on the tuber itself as well as the outside of the container the tubers will be stored in (I do one variety per bag).

Location

In a perfect world, dahlia tubers like to be stored in 40-50oF temp with 80% humidity. Unless you have a cooler where you can adjust the temp and humidity, this is probably tough to achieve.

For us backyard gardeners, we’re looking at something more like an unheated garage, crawl space or root cellar that is a dark, cool space free of direct sunlight, swings in temp and added moisture.

Medium

This is different for each person depending on their environment. The medium in which you store your tubers can be:

1.     Shredded newspaper

2.     Vermiculite

3.     Wood shavings

4.     Peat moss

5.     Syran wrap – if using this method, each tuber is individually wrapped in syran wrap. I’ve never tried this method, but the people who use it seem happy with it because no two tubers are touching so if one rots, the rot won’t spread from tuber to tuber unlike if they were all stored in one container in the same medium.

Each of these mediums are usually contained in something like a Ziploc bag, plastic shoe box or cardboard box.

I use:

• Vermiculite filled Ziploc bags stored in cardboard boxes in my unheated garage. I keep the Ziploc bags open a couple inches so condensation doesn’t fill up the bag. I like to completely cover my tubers in the vermiculite and do one bag per variety.

  
  

Overwintering in the ground

Make sure to mulch with several inches of organic material such as leaves, straw, wood

chips, etc. I’m not sure if covering with plastic or a tarp would work as well or if it would trap too much moisture. The tubers I accidentally overwintered in my raised beds were covered with a couple inches of leaves and I had row covers with Agribond-50 frost cloth over the raised beds. Consider researching other gardeners in your growing zone to see what they recommend!

9.     Dividing tubers

• You can choose to divide your tubers in the fall after digging them up or in the spring when the eye is visible so you’re not wasting storage space for tubers that won’t grow.

• When dividing tubers, it’s important each tuber has the anatomy we discussed at the beginning of this post: an eye, crown, neck and body.

• I like to use a pair of thin nosed Fiskars snips, Felcos or sometimes scissors (NOT fabric scissors! IYKYK)

• Carefully cut the crown away from the stock and gently untangle the tubers from one another. I like to cut away any small, stringy tubers and extra roots.  

• You may notice one tuber looks a little darker and has a lot of roots coming from it. This is the mother tuber. Some people choose to keep it. I toss it because she’s done her job. The mother tuber is the original tuber you planted in the spring!

• Once the tubers have been divided, at this point they can either be stored if it’s fall or planted if it’s spring and fear of frost has passed.

10. Pests and Disease

    All dahlias have viruses. That’s just how it is. No matter how extreme your cleaning practices are, these are live plants living in live soil surrounded by live bugs that carry all sorts of things with them.

    
    

    I take the approach of "when in doubt, throw it out." Another approach to help stop spread between plants is to sanitize your snips with a bleach or alcohol solution in between plants so as not to spread disease or viruses from plant to plant.

    
    

    Here are some of the things you can run into with your dahlias. These will vary by region (especially the insects), but here are some common ones I've run into in Knoxville TN (zone 7a).

Disease/Pest

Viral

Gall

Insects

Bacterial

Rot

What you may find

Veins of the leaves are yellow or spotted, plant is stunted and may not flower.

Crown gall and leafy gall caused by bacteria.

Leafhoppers, Thrips, Cucumber Beetles, various caterpillars (i.e. armyworms, moths, etc.), Japanese Beetles eat the leaves and/or blooms.

Asters Yellow, Gall, Rotten Tubers

Overly wet conditions, bacteria penetrating damaged tuber.

What to do

Throw out the plant and do not keep tubers.

Throw out the plant and do not keep tubers.

Beneficial insects, spray every 5-7 days depending on infestation, hand pick beetles into soapy water.

Some of these are transmitted by insects to the plants, others are from the soil and damage to the tubers. Throw out plant and tubers.

Remove rotten tubers. Save viable tubers. Possibly save cuttings from the plant and root to grow a new one.

Leaf hopper and their damage to leaves

Leaf burn from pests

Aster Yellows

Damage from unknown moth caterpillars

Japanese Beetle

Unknown moth caterpillar eating leaves

Japanese beetles damage flowers and leaves

Rotted tuber completely disintegrated from plant.

11. My favorite varieties I can't live without

Some varieties of dahlias are notorious for being highly productive with both tubers and blooms, great or poor in storage, produce minimal blooms/tubers, "unicorns". Over the past 5 years I've grown a variety of dahlias and here are some of my favorites.

Strawberries and Cream

Rock Run Ashley

Robinhood

Robinhood

Peaches

Critchon Honey

Pink Sylvia

Diva

My Forever

Nathalie G

Chewy

My Forever

• Diva - The first dahlia I ever grew and never looked back. A late bloomer, but worth the wait. A beautiful decorative variety that is a deep purpley-red.

• Chewy - A ball variety that has the most amazing color pallet: orange, yellow, pink and purple all in one!

• Strawberries and Cream - This gal is reliable, pumps out the blooms on stick straight, long stems all season long and produces a great clump of tubers.

• Peaches - another decorative variety like Diva, but the prettiest peach/cream color you ever saw.

• My Forever - a waterlily variety that is a beautiful apricot/yellow that will stop you in your tracks.

• Pink Sylvia - a ball variety of the most perfect pink you ever saw. She also produces great tubers.

• Robinhood - I never knew red, pink and purple could look so great together, but the depth of color in each petal is mind blowing.

• Nathalie G - This gal was one of the first dahlias I grew at a large scale and one I get excited to see every year. Similar to Linda's Baby and is one of the first to bloom alongside Strawberries and Cream.

• Critchon Honey - Such a beautiful creamy yellow with a darker center. A bush variety meaning it will not grow tall, but that doesn't stop it from pumping out the blooms!

• Rock Run Ashley - If I had to grow one flower for a wedding, this would be it. A beautiful blush, almost pink/mauve, muted but stunning.

 What would you add? Do you have any favorites I haven't mentioned?

Let's start a conversation! I'd love to chat if you have any questions. Ask below or reach out via email at taylordbakesandbloomsllc@gmail.com