Dahlias are grown from tubers and not bulbs. Tubers have “eyes”, for example a potato is considered a “tuber.” Bulbs, such as tulips and daffodils, can be planted in the fall when the ground is cold and wet. Dahlias must be planted in the spring when the soil has warmed to a temperature of between 55 – 60 degrees.
Basic top soil is a good soil to use for dahlias. If your soil is depleted and you do need to amend your soil, lay a 4″ layer of compost on the garden bed and till/work into the soil. You can also amend just the planting hole with compost and mix in. Be careful not to amend your soil so that it is too rich in organic matter. Dahlias originated from the mountains of Mexico and thrive in even average soil that is well drained.
We find that planting in rows and mounding up your soil will benefit in many ways. See example below. The mound doesn’t have to be too tall, approximately 6″ will be enough. The soil will drain better, be warmer and the soil will be softer for the dahlia to stretch out create it’s tubers. If you live in an area that has fall rains, when the rain does come back, your dahlias will be “up” and out of the mucky soil making for easier digging. You’ll have less breakage of the tubers because the soil will be less soggy and heavy. Less chance of the tubers rotting as well.
Where to Plant
Plant your dahlias in a sunny location that receives at least 6 hours of sun per day. Morning sun/afternoon shade works best in warmer climates.
When to Plant
A good rule of thumb to follow: When it’s safe to plant seeds outdoors in your area, it’s safe to plant your dahlias.
Don’t plant to early, planting time in the North is mid-late May as temperatures allow. Warmer, southern states are usually safe to plant April, as temperatures allow. Delay planting if you’ve recently had heavy rains that have resulted in soggy soil. Dahlias like to be planted in moist soil, that is not water-logged. Don’t plant your dahlias in an area where water has a tendency to sit.
Space your dahlias 18″ – 24″ apart, 12″ for a fuller, more grown together look. Lay the dahlia tuber on its side (flat), about 4-6″ deep with the eye of the tuber pointing up. Do NOT water at planting time, during normal springtime rainfall, the soil has enough moisture to fulfill the dahlias needs until it has sprouted above ground. An exception would be dry climates where the soil would need to be moistened for planting.
Dahlia Barn Field – North Bend
DO NOT WATER WHEN YOU PLANT !! Spring time offers enough rain to fulfill the tubers needs until the sprouts appear above the ground. An exception would be an extremely dry climate where the soil would need moisture added, but if your soil has plenty of moisture, don’t water at planting time. Dahlia tubers are susceptible to rot after planting, especially in soggy, wet soils. At first, it’s best to keep the soil on the dry side, rather than the wet side. Don’t water until you see the sprout above the soil. Then begin to water 2-3 times per week with a deep soaking. We highly recommend using soaker hoses to water your dahlias. The water goes directly to the root zone and keeps the leaves dry, preventing fungal diseases. Run the water as long as it takes to deep soak the soil to a depth of around 4″ minimum. We generally have to run our hoses for 30-45 minutes to get a deep soaking in Washington State. Warmer, dryer climates may need to water at least every other day. Once the dahlia has sprouted, a deep soaking 2-3 times per week in the summer is sufficient.
Dahlias require low nitrogen fertilizers. We recommend fertilizers with a 5-10-10 ratio, or as close as you can find to a 5-10-10 ratio, within 30 days of planting and again 30 days later. Do Not overfeed your dahlias, doing so will promote lots of foliage, but not a lot of bloom. Fertilizer makes foliage and water makes bloom. Proper watering and good soil will create the best flowers.
Hand weeding is the only type of weed control you should use. Using herbicides around your dahlias is risky!
Pests & Problems
SLUGS LOVE DAHLIAS !! Especially as they are emerging from the soil. Use the slug bait of your choice until your dahlias are at least 12″ tall. After the dahlia has reached full height, no slug bait is necessary.
DEER – We find that deer DON’T like dahlias. Deer will stroll through our gardens, eat blackberries and apples, but leave the dahlias alone. We have mostly Elk in Washington, but a fair amount of deer as you can see in this picture.
EARWIGS – Not much can be done about earwigs. You can spray over-the-counter insecticides or insecticidal soap. Granular insecticide sprinkled on the soil will help as well.
Pinching your Dahlias
To promote a compact, bushy plant with more blooms, pinch out the center growing tip right above the 3rd full sets of leaves for the large dinner plates dahlias. Pinch higher on the smaller blooming varieties, above the 4th or 5th full set of leaves, when the dahlia is 12″ – 18″ in height. This will create a stronger, more manageable plant with more blooms. It will also make the plant less top heavy to where you have a need for staking.
The more you cut dahlias, the more they will bloom !! You want to cut yourself a long stem as well, even it if means taking the 2 side buds. This will promote more
Dahlias – The more you cut them, the more they will bloom.
growth and more blooms. We tell people in our U-Cut gardens to cut a stem no shorter than from your wrist to your elbow.
Dahlias can be susceptible to powdery mildew and other types of fungus. Keeping the leaves dry as possible will help to control fungus. Fungus thrives in wet conditions. At the first sign of any fungus, spraying with any type of fungicide every 7-10 days, until the fungus is under control. Preventative sprays can be used to control fungus from starting and spreading. Neem oil*, derived from the ‘Neem Tree’, is an organic approach and is a natural Fungicide, Insecticide and Miticide. It also makes the leaves shiny and green and can be used up until and even after the dahlia is in bloom. *You can find Neem Oil at most garden centers.
Only if you had any problems with fungus on your dahlias last summer, soaking them in a mild bleach solution will kill any overwintering fungus. After cleaning up the tuber clump or dividing your tubers, soak them in a mixture of 1/2 cup household bleach to 1 gallon of water for 15 minutes. After soaking, rinse tubers thoroughly with clean water. Let dry for 3-5 days in an environment that is above freezing, then store for winter.
Wait until your dahlias look like this before digging !!
WAIT FOR YOUR DAHLIAS TO FREEZE IN THE FALL !! Don’t be in a hurry with your dahlias, they need to feel the cold. Then wait at least 1-2 weeks before you dig them up. Leave them intact and don’t cut them down. Wait until the foliage has turned black and have completely died back. During this time, the dahlia is ‘ripening’ and preparing itself for winter. Dahlias dug too early will not store over winter. After the foliage has died back, cut the stems to a height of 6″-8″. Use a shovel or pitchfork to gently loosen the soil and lift the clump out of the soil. Tap off the soil from the clumps and allow the clumps to dry in an area above freezing for at least 3-5 days. You can divide then or leave in a clump and divide in the spring. Then store for winter.
Do I really need to dig up my dahlias?
Digging and dividing will keep your dahlias returning year after year when they are dug and stored properly. Dahlias left in the ground will create a massive tuber clump underground that will send up many weak, unproductive stalks that have small blooms. Eventually, if left undug year after year, they won’t come back at all. You can treat your dahlias as annuals and purchase new tuber stock each year.
If you live in an area that does not have harsh, freezing winters, your dahlias may survive winter without digging. In the fall, wait at least 1 week after a freeze and after your dahlia stalks have died back completely. Then cut the stalks down to the ground and place a 10″-12″ layer of mulch such as grass clippings, leaves, straw or compost. This will protect your dahlias over winter. In March, remove the layer of mulch so that the soil can begin to warm up. Dig up the tubers, divide, let dry for 3-5 days, and replant them when it’s the correct planting time for your area.
Although, we do recommend digging, dividing and storing in the fall, you should have success with this method as well.
Tap and brush all the soil off the dahlia clump. When dividing dahlias, the first thing to do is to remove all broken tubers, remove the original ‘mother’ tuber and remove any tubers that are rotten. You can divide now or keep the cleaned-up clump in tact and divide in the spring. In the spring, the eyes are easier to see. It’s very important to get a piece of the swollen part that is attached to last years’ stem. The eyes will emerge from the swollen part of the dahlia that is attached to last years’ stem. If your tuber does not have an eye, it will not sprout. Choose only strong, firm tubers. Weak tubers that show signs of rot, shriveling or decay should be tossed and not used in the garden.
Cut surfaces should be allowed to dry thoroughly before they are planted in the garden or stored for the winter. Lay out to dry for 3-5 days in a place that will not freeze, then store for the winter.Our step by step tutorial of the tuber dividing process:
Dahlia Barn tubers
Just look at or Print a printable copy (PDF)
Easy Winter Dahlia Storage / Warmer Climates
Click on image for larger photo
There are many different ways to store your dahlias. We’ll give you a few different methods. Choose the method that you think would be right for you. If one method doesn’t work, try different ways of storing from year to year and stick with what works best for you. You can be as fussy or carefree as you need to be with your dahlias.
The most important tips are:
Make sure they never freeze wherever they are stored.
Make sure they are dry before they go into storage.
Some people will use a peat moss method below for colder climates. Other options are:
Store in clump form or divided loose in paper or plastic bags. No peat moss.
Cardboard boxes, wood boxes, plastic boxes or coolers lined with newspaper.
Keep the temperature at 40-50 degrees at all times during winter storage. The humidity should be kept medium-high to keep tubers from drying and shriveling. Check your tubers at least once a month during winter storage. If they do show signs of shriveling, give them a spray of water from an ordinary spray bottle.
Winter Dahlia Storage / Colder Climates
You can follow the directions for Easy Winter Dahlia Storage / Warmer Climates if you have an attached heated garage or cellar. You can store anywhere that the temperature will stay 40-50 degrees and never freezes. Outside sheds in colder climates will freeze and are not recommended as a place to store your dahlia tubers.
Start with a cardboard, wood or plastic box lined with newspaper.
Our eastern Washington Dahlia Barn.
Add a layer of peat moss for added protection from cold temperatures.
Add your dahlia tubers in clump form or divided.
Add another layer of peat moss.
Add another layer of dahlia tubers.
Repeat the process until your box is filled. You may need more than 1 box if you have a large amount of tubers.
Check your tubers monthly during winter storage. If they appear to be shriveling, take a spray bottle and spray them with water. In the spring, after all danger of frost has passed, bring your dahlias out and divide them if you didn’t already divide in the fall. Let the fresh cuts dry for 3-5 days, then plant in the garden when it’s the correct planting time for your area!!
Dahlias do require a fair amount of care and maintenance throughout the year, probably more than the average garden plant. But for all your work, you will be rewarded with armloads of fresh cut flowers during late summer when most other garden plants have finished their bloom. Cut the flowers and enjoy their blooms. The more you cut them, the more they will bloom.