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Dahlia Care

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.  We plant in mid May in the Pacific Northwest.

Soil Preparation

The best place to plant your dahlias is in an area that’s already a garden area that has basic top soil.  To prepare for planting, amend your soil with a 4″ layer of compost on the garden bed and till/work in before you plant.

***  If you are creating a brand new area for planting:  Use 3-Way Top Soil, which is a mixture of top soil, manure and sand.  3-Way can be delivered by your local nursery or you can buy it by the yard and haul it in your truck or trailer.

Where to Plant

Minimum sun requirements for dahlias is 6 hours per day.  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

Don’t plant to early, dahlias need the soil to reach 60 degrees for best results.  Planting time in the Northwest is around Mother’s Day.  Areas in the far north, such as VT, NH, MN, MI, planting time is late May or as temperatures allow.  Central US, in April when soil allows.  Warmer, southern states are usually safe to plant late March, early April, or 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.

Planting

Space your dahlias 18″ – 24″ apart, 12″ for a fuller, more grown together look.

Lay the dahlia tuber on its side (flat), about 6″ deep with the eye of the tuber pointing up.  Cover with soil.

Dahlia Barn Fields

Dahlia Barn Field – North Bend

Watering

DON’T WATER WHEN YOU PLANT !! That’s hard to do with new plantings, but spring time offers all the moisture the tubers need.  Do not water until the sprouts appear above the ground. An exception would be an extremely dry climate where the soil would need moisture added, dahlias do need some moisture to the soil to get growing.  If your soil has plenty of moisture, don’t add extra 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. When you see the sprout above the soil, begin watering 2-3 times per week with a deep soaking.

Easy Watering

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 6″ minimum. We generally have to run our hoses for 45-60 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.  The soil should never completely dry out or they will stop growing properly.

How long until they bloom ?

Small-medium bloom size dahlias will take about 90 days to bloom.  Large dinner plate dahlias will take about 120 for bloom.  Soil moisture is so important at this time.  Be sure to supply your dahlias with enough water to keep them growing strong and healthy.

Fertilizer

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.

Weed Control

Hand weeding is the only type of weed control you should use. Using herbicides around your dahlias is risky!

Pests & Problems

Deer 1

Can you spot the deer?

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, but they will eat what they want if they get hungry enough. Deer do stroll through our gardens, eat blackberries and apples, but leave the dahlias alone.

EARWIGS – Not much can be done about earwigs. You can spray over-the-counter insecticides or insecticidal soap. Granular insecticide sprinkled on the soil in the springtime 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 4th or 5th full set of leaves,  when the dahlia is 18″ – 24″ 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.

Cut Flowers

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 growth and more blooms. We tell customers to cut a stem no shorter than from your wrist to your elbow, minimum even if it means taking the side buds.  We find, the side buds to be weak flowers.  This will promote lots of growth and make for a healthier, more manageable plant with lots of blooms.  Dahlias are work horses and love to be cut.

Diseases

Dahlias can be susceptible to powdery mildew and other types of fungus when they are in wet conditions. Keeping the leaves dry as possible will help to control fungus, because 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.

Digging Dahlias

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.

What if I live in an area that doesn’t freeze?

You are safe to dig around mid-November if you haven’t gotten a freeze.  Start to with hold water for about 2 weeks before you dig, around November 1st.

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.

Dividing Dahlias

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:

 

Just look at or Print a printable copy (PDF)

Winter Dahlia Storage

There are many different ways to store your dahlias. 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.

The most important tips are:

  1. Make sure they freeze in the garden and the stalks turn black before they are dug up.  During this time, the skins are thickening and they are preparing themselves for winter.  Dahlias dug too early typically will not store over winter.

  2. Once dug up, make sure they never freeze wherever they are stored-an attached garage or a cellar is usually pretty safe.

  3. Make sure they are VERY DRY before they go into storage.

 Storage options are:

  1. Store in clump form or divided loose in paper bags or cardboard boxes lined with newspaper and filled with peat moss.

  2. Cardboard box lined with newspaper, add a layer of peat moss, add a layer of dahlias, another layer of peat moss, etc until the box is full.  This can give you an added layer of protection from freezing and keeps humidity higher.

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 monthly during winter storage. 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.