Learn to grow dahlias using these tips to start your tubers in spring, extend the summer blooming season, and store them over the winter for blooms again next year. By avoiding common problems, you can enjoy these gorgeous plants for years to come.
How to Grow Dahlias
I gathered these tips for growing dahlias from numerous sources including books, research papers, my own experience, and advice from professional growers whose livelihood depends on their success.
While methods and opinions vary, if the basic needs are met, you should do just fine.
I’ve provided seven top tips and answered Frequently Asked Questions for an excellent overview of everything needed to grow dahlias.
Dahlia | Genus: Dahlia | Asteraceae family
Dahlia Growing Tips
Tuberous herbaceous perennial native to Mexico and Central America
• 42 species | 57k cultivars
• USDA Hardiness Zone: 8 up
Grow with winter storage: zone 2 up
• Sun: 6+ hours full morning sun
• Soil: pH 6.5, does not like damp or dry
• Start indoors: 4 to 6 weeks before last frost
• Plant outdoors: after last frost, soil 60°F (16°C)
• Propagation: seed, tubers, cuttings, grafting
• Flowers: mid-summer through to fall frosts
• Cold climates: store tubers for winter at 40-45°F (4-7°C)
• Pollinators: mainly bees and beetles
• Larval host plant: various Lepidoptera, specifically moths
Watch Quick Dahlia Growing Tips
1Start Your Dahlias Indoors For an Earlier Bloom Time
Dahlias take 90 to 120 days to flower after planting, depending on the variety you are growing.
Generally, the larger the plant and flowers, the longer it takes.
If you want flowers before late summer, consider starting your dahlia tubers indoors in pots 4 to 6 weeks before last frost. This head start provides a longer flowering season.
2Tag Your Dahlias So You Know What to Expect
While dahlias are not frost hardy they are perennial and this means we can grow the same tubers year after year—if they are protected from freezing temperatures with winter storage.
But, with so many different species (42) and cultivars (57k), there are many different flower shapes, colors, and plant sizes—and different needs—and there is no way to identify them by looking at the tubers.
Tags to the rescue! By keeping track of each dahlia both through the growing season and in storage, come planting time, you’ll know what it needs and where to plant it.
3Stake Your Dahlias at Planting Time (Not After)
The wonderful thing about dahlias is the massive flowers, of course, but they tend to be top-heavy and pretty much always require support to avoid stem damage.
Save yourself future trouble by installing the support post right at planting time. This avoids accidental puncturing of the tuber later.
With a good support post (rebar, pipe, wood) placed next to the eye of the tuber (see the planting tips below), the main stem of the dahlia will grow right where you need it.
Twine is added as the plant grows. Make a loose loop around the stem and a tight loop around the support pole to keep things in place without damaging the plant.
See more about Staking Dahlias here.
4Don’t Be Afraid to Pinch Your Main Stem
While you can leave your dahlias to grow without any grooming, you may want to ‘pinch back’ the main stem once there are several sets of leaves.
Pinching back (the same as cutting off) the main stem encourages the plant to become bushier and put more energy into lateral shoots and additional blooms.
Alternately, growers who enter their dahlias into flower-growing competitions may remove all the lateral stems leaving the main stem to produce a single, spectacular flower.
See more on Pinching, Grooming, and Topping here.
5Grow in Containers to Discourage Slugs and Snails
If your garden tends to be a magnet for slugs or snails, consider growing your dahlias in containers.
Often miniature dahlias are recommended for pots but you can certainly try growing any size dahlia this way.
In my experience, the larger the container, the better. And, with the pot off the ground, the chance of slug or snail feasts is greatly reduced.
Learn more about possible Pest and Diseases here.
6Grow Dahlias in Full Morning Sun
Dahlias are one of those plants that like their soil moisture nice and even.
If the soil holds too much moisture, the tubers, especially in the first few weeks, are prone to rot.
And, if the soil dries out, they can wither and die.
If you can, choose a location with full morning sun so they get maximum light without direct exposure to hot, drying afternoon sun.
Read more about Watering Dahlias here.
7Store Your Tubers in Plastic Food Wrap for the Winter
Every enthusiastic dahlia grower will tell you their storage method works like a charm. And—they are right—for their specific conditions. The point is, it’s the health of the tuber and the overall environment that counts.
The optimum storage temperature is 40-45°F (4-7°C). We run into problems when the heating systems in our homes make the humidity level too low for the tubers.
If this sounds like your situation, consider using the plastic food wrap method (more on this below). Each tuber is wrapped individually to keep moisture in. Growers who use this method report a higher number of viable tubers each spring.
Read more about Winter Storage Methods here.
Frequently Asked Questions & Growing Tips
1How Do Dahlias Grow?
Here is an overview.
You can grow dahlias at home from seed, tubers, or cuttings.
The most common and quickest way to get started is growing from tubers (also known as root tubers or roots). These are similar in appearance to sweet potatoes and get planted in spring. You will see them for sale in stores in early spring.
When you buy tubers there might be one tuber total or a cluster of them growing together. Either way is fine.
Dahlias grow their main stem from the ‘eye’ of the tuber. Unlike potatoes which form eyes in several locations, these eyes only form on the crown (located on the ‘neck’ of the tuber).
It’s the main stem that produces leaves and lateral shoots which in turn form buds which become blooms.
While dahlias are perennial, they are not winter hardy below USDA zone 8. But exposure to some cold is necessary for their development each year so we wait until early frosts have blackened the foliage before digging up the tubers and storing them for the winter.
Come spring, they can be started a few weeks early indoors or planted directly outdoors after last frost.
2How Do I Know a Dahlia Tuber is Good?
Beware of Mush and Mold
If shopping in-person, have a look at the tuber (if you can) before purchasing.
Otherwise, look it over when it arrives in the mail.
Always have clean hands and handle with care.
You want to be sure the tuber is disease-free and firm like a good sweet potato, not shriveled or squishy.
You may also notice the eye which grows on the crown located on the neck. A tuber without an eye can’t grow a stem or flowers.
Check the plant tag for any special planting needs and what the mature dahlia will be like. Flowers size and height can vary dramatically from one-foot to six-feet tall.
The fine print may also say whether or not that particular variety is a good candidate for winter storage. Some dahlias are best just as annuals—one and done. Others can keep producing flowers for years when stored properly.
3How to Tag and Track Dahlias
When it comes to dahlias, tags and tracking are your friends.
Unless you’re growing just one, take the extra step and keep it tagged. As mentioned, there are tens of thousands of varieties and tremendous range of flower shapes, colors, sizes, and heights.
Some varieties like single or collarettes do not even look like dahlias. They are still beautiful but often mistaken for other flowers.
You’ll want to know what you’re planting each year so you can provide the best growing conditions and put that particular dahlia where it will look just right.
Marking Pen on the Tuber
Before planting, write the name or a code for the name (remember to write down what your code means) directly on the dry tuber with a permanent marking pen. This is an easy tracking method while in storage. The marker will not harm it but it may fade or distort as the tuber grows.
There is more on preparing the tuber for winter storage here.
Also have corresponding plant tags or markers to keep with your dahlias as they grow. I attach mine to the support stakes. For extra insurance you can also bury a plastic name tag with the tuber and retrieve it in fall.
4How Long Do Dahlias Take to Flower?
Dahlias need 90 to 120 days to flower
Flowering time depends on the variety. Some take approximately 90 days (3 months) from your planting date. Other larger cultivars may take as long as four months or 120 days.
Check your product package. This may determine whether it’s worthwhile starting them early indoors.
5Dahlia Planting Instructions
Start dahlia tubers indoors 4 to 6 weeks before last frost or wait until the risk of frost has passed and plant directly outdoors. The longer it takes to flower, the earlier you can start it.
The advantage to starting your tubers indoors is you get a jump start on the growing season and may see flowers up to a month earlier than you would if you planted directly outdoors later.
Approximately 4 to 6 weeks before last frost, plant your tubers in sterile potting mix in the largest containers you can manage. Start the ones that take longest to flower the earliest.
You can use small container (4-inch pots or whatever is large enough for the tuber to fit laying flat) or 1-2-gallon pots. If I have room, I use larger pots and may continue container growing outdoors as well.
Use the planting depth recommended on the plant label (usually 6-inches) with the tuber laying flat.
Provide full sunlight or place 6-inches below grow lights, water sparingly—but never let it dry out. To start growing, there must be moisture in the potting mix.
Gradually introduce your dahlias to life outdoors (harden them off) after last frost. You can continue growing them in pots or transplant them.
Will Dahlias Bloom Indoors?
As a one-season annual, maybe. And it could be a long flowering season before it finishes.
I could not find an example online but theoretically you should be able to plant your tuber in a pot and, with enough light and consistent moisture, get it to bloom indoors. And the keyword is light: it takes a lot to get them going.
So, assuming you got the dahlia to flower indoors, it will still need exposure to fall frosts eventually to prepare for winter storage, so that will require sorting out.
If you have tried this or know some examples, send me an email. It’s definitely worth experimenting.
It’s outdoor planting time after last frost in spring or early summer when the soil temperature is consistently 60°F (16°C) over several days.
A handy rule is, if it’s the right time to plant tomatoes, it’s the right time to plant dahlias.
Ideally, choose a location with full morning sun and part-shade in the afternoon. This prevents the hot afternoon sun from potentially drying out the tubers.
The soil should be rich and well-draining.
Dahlias should be placed approximately 1 to 3 feet apart, depending on the cultivar (check your label for instructions) and avoid placing them in competition with other plant roots nearby.
Most instructions recommend planting the tuber around 6-inches deep, laid flat, with the eye or shoots aiming up. Make the planting hole at least 12-inches in diameter and (usually) six-inches deep.
If your dahlia already has a shoot and leaves, remove the lowest set of leaves (the cotyledon or embryonic leaves) and plant so the first true leaves are just above soil level.
If your soil is already moist and you get regular rainfall, avoid the impulse to water your newly planted tubers. It’s during this stage that the tubers tend to rot if over-watered.
Later on, as the plant gets big and flower form, you will water more often.
Because dahlias need support—the flowers are very top-heavy—place the taller varieties behind smaller plants in your garden beds so you can enjoy the flowers without seeing the stakes.
Always put your stakes (or whatever supports you are using) in place at planting time.
Use any very sturdy metal like rebar or pipes or wood rods or posts tall enough for the mature height of the dahlia plus a foot to submerge in the ground or container.
Position the stake right beside the eye on the tuber (at planting time). This way the main stem will grow next to the stake and you don’t run the risk of puncturing the tuber by adding the support later.
If you are growing masses of dahlias in a bed, look into horizontal mesh netting options.
As the dahlia grows you will add twine loops, loose around the plant, tight around the stake, to support it every foot or so.
Overwintering Dahlias in the Ground
Depending on your growing zone and how cold your winters get, you may be able to leave your tubers in the ground for the winter.
Success will depend on a whole bunch of factors including the variety you are growing and how wet and cold it gets.
When I lived in zone 5, I kept my dahlias (variety unknown) in the ground all year-round. To further insulate them in the winter, I covered the area with a foot of straw mulch. This was enough to prevent freezing.
If your ground doesn’t freeze deep down, in-ground storage (leaving the tubers in place) may work.
6Growing Dahlias in Containers
As mentioned, dahlias can be started in containers indoors in early spring or planted directly in containers outdoors after last frost.
Some advice says to only choose shorter dwarf or miniature varieties because the container may otherwise stunt its growth.
Personally, I have grown really large dahlias (5-feet tall with big flowers) in 2-gallon pots without any problem. I’m sure success will vary depending on the specific variety and growing conditions.
Using containers makes it very easy to dig up the tubers at the end of the season for winter storage. Plus, I like being able to move the plants around to avoid heat waves and rain storms that may damage the plants.
The goal is even moisture. We don’t want the soil so dry that the tubers shrivel up, but neither do we want it so moist that they rot.
Your watering routine will depend on your growing conditions and weather.
If you get really hot afternoons like we do, mulch around the base (without the mulch touching the stem) to retain moisture and water as needed.
Dahlias need more water as they grow.
Some avid growers use drip lines or tapes to get water to the roots. Soaker hoses may only penetrate the first inch or two of soil.
8Pinching, Grooming, and Topping
I grew dahlias for years without any grooming, but, as you gain experience, you may want to ‘pinch’ (remove the top of) the main stem for a better outcome.
The purpose of topping or pinching is to create a bushier plant by removing the upper section of the main stem from the tip down to a leaf set, which forces the dahlia to branch out more.
This is done once in the season and some experienced growers say the sooner the better.
If you are really keen, look up your specific variety for instructions, otherwise, wait until there are between 2 to 4 sets of true leaves and the plant is at least a foot tall. The lowest set of leaves doesn’t count because they are cotyledons (embryonic leaves not true leaves).
That may be all the grooming you want to do.
Disbudding is a little more advanced method for growers wanting the biggest and the best flowers.
On each plant, dahlias produce a number of buds that can become flowers. You can remove all but one bud on each stem for greater but fewer flowers.
Disbranching is just what it sounds like: removing entire stems (branches, not the main stem). It’s the opposite of topping or pinching really because instead of encouraging side growth we’re halting it entirely.
Whatever you do, always wash your hands and disinfect your gear before and after handling each plant. Dahlias are susceptible to various transmittable diseases.
9Should I Fertilize My Dahlias?
This may come down to how environmentally-conscious you wish to be. The quest to produce show-worthy flowers tends to ignore the environmental impact of our choices. A home grower may be very happy with their dahlias without extra care.
There are successful dahlia growers who swear by their fertilizers (the right one at the right time) and those who don’t find it necessary.
Personally, I’m just a casual grower and I just rely on good old compost in my soil for nutrients, avoiding synthetic fertilizers and never tempted by commercial organic ones.
Those who do fertilize have different timings: some say to do the first application a month before planting, others say at planting time and then a month later.
All agree you should avoid high nitrogen, otherwise your dahlia will be all foliage and no flowers.
For specific N-P-K amounts, I’ve seen water soluble or granular fertilizers with 3-5-5 and 5-10-10 recommended.
Dahlias are heavy feeders so do investigate this further if you think your soil or potting mix doesn’t have what it takes.
As mentioned, dahlias can be propagated by seed, tubers, or cuttings. Grafting is also possible.
Growing from tubers (as described here) is the most popular method.
You can also raise your tubers just for cuttings, to get many plants from one, or take cuttings from your dahlias during the growing season.
Growing from cuttings is quite economical, sometimes generating as many as five new plants from each tuber.
If you want to root dahlia cuttings from an existing plant, the method is the same as the softwood cutting technique shown here.
If growing from seed, follow the instructions on the seed packet.
And don’t forget to divide your tubers when they multiply: so long a there is an eye on each section, you can grow a new dahlia.
11Dahlia Pests and Diseases
- Watch for slugs and snails, especially around the young plants.
- Earwigs disfigure the blooms.
- Aphids go after the stems and immature flower buds.
- Red spider mites dine on the foliage.
- Capsid bugs create holes on the stem tips.
On a brighter note, while not entirely deer-proof, dahlias are not their first food choice when other plants are available.
Possible diseases include powdery mildew, grey mould (Botrytis cinereal), verticillium wilt, dahlia smut (Entyloma calendulae f. Dahliae), phytopthora, and other plant viruses.
There is a list here on Wikipedia: Dahlia Diseases
12How to Store Dahlia Tubers for the Winter
Dahlias need some frosty weather to prepare them for winter dormancy. It is believed that the longer they can be exposed to cold without freezing, the better they will grow in the future. But it is a juggling act to make sure you retrieve them before real winter weather sets in.
- During the growing season pay attention to which of your dahlias do best and those that are meh or under-performing.
- Mark the best ones as candidates for winter storage. I use pieces of ribbon tied to their supports to indicate the keepers. A meh tuber is not going to improve next year.
In fall, keep your dahlias growing until the plant has blackened from a few good frosts.
At this point some growers trim off all but about 6-inches of the main stem and wait a week or two longer before digging them up. I fold over the stem and hold it in place with an elastic band so water doesn’t get in it (tuber rot paranoia).
Use a digging fork to ease the tubers out of the ground. Work at least a foot away from the plant and dig deeply to avoid any chance of injuring the tubers.
At this stage, your single tubers have probably multiplied (yay) and there may be a bunch all joined together.
Get them out of the ground and prepare them for storage.
Preparing Tubers for Storage
This is another topic where there are as many methods as there are gardeners. Read all the way through to understand why tossing them in the cold room, like our grandparents used to do, may or may not work.
Keep in mind that your tubers may also benefit from dividing before storage.
Sterilize your gear and wash your hands before handling them to avoid spreading disease.
Some gardeners just tap off the excess soil before and after air drying, others wash the entire tuber in water and brush away all traces of soil.
Some gardeners also treat the cleaned-up tubers with fungicide or dip them in a 1:10 bleach/water solution.
You always want to discard any dead, damaged, or diseased tubers and just keep the good-looking ones.
You can divide tubers now—before storing them—if the eyes are visible. The video shows helpful examples.
The other option is to divide them in spring but be forewarned that some tubers toughen up so much over the winter that they can be very difficult to slice.
I’m a do-it-now person if the opportunity is there.
“But my grandparents just tossed the tubers in a paper bag and stashed it in the cellar and that worked fine….”
Yes, that easy method can work but only if other conditions happen to be optimal—things we don’t think about if everything is going well.
The optimum storage temperature is between 40-45°F (4-7°C) with medium to high humidity.
The goal is dormancy in a cool, dark place.
Too warm or dry and they may wither or rot. If they freeze, they do not survive.
Even if you provide excellent storage conditions, about 10% of tubers will not grow again, depending on the variety. The plastic wrap method (below) seems to do best with approximately 95% regrowing.
1Plastic Food Wrap Method
Wrap each tuber individually in plastic food wrap, label with names on affixed pieces of tape, place in box one inch apart and store. You can also write the name directly on the dry tuber with a permanent marking pen.
2Paper Bag Method
Place loose tuber or clump of tubers in one bag each and store.
Wrap each tuber or clump in newspaper, store without touching others.
Place tubers (not touching each other) in container filled with any of the following:
Coarse vermiculite, wood shavings for pet bedding, dry (disease-free) leaves, or moistened sand.
If humidity level is low, cover with lid with air holes.
Check your tubers every few weeks and discard anything moldy or shrivelled. I set a reminder on my phone for this.
If conditions are too dry, add moisture.
As outdoor conditions begin to warm, your storage area may too.
Eyes will begin to develop as the tubers warm up. Be sure tubers do not dry out.
Start them indoors 4 to 6 weeks before last frost or wait and plant directly outdoors after risk of frost has passed.
Can I Still Grow a Shriveled Dahlia Tuber?
Sometimes. So long as it is not diseased, it is sometimes possible to re-hydrate a shriveled dahlia and grow it as usual. You’ll likely know by looking at it if it is too far gone.
To re-hydrate a tuber:
- Wrap the tuber in a moistened paper towel (not dripping wet) and sit it in an open food bag or container in a warm location like a kitchen cupboard.
- Check daily to see if it is plumping up again. Give it two weeks to recover.
- Dahlia Societies and Conferences | Canada and United States
- Dahlia Databases and Suppliers | Dahlia Addict (North America)
- Dahlia Research | Researchgate.net
- No Fuss Plastic Wrap Storage | The American Dahlia Society
And that’s a wrap. Go grow some dahlias!
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~Melissa the Empress of Dirt ♛