Dahlia Care

Dahlias are grown from tubers, 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 60 degrees.  Plant when you would plant warm season crops, like your annual flowers or your vegetable garden.  We plant in mid May in the Pacific Northwest.

Soil Preparation

Dahlias need well drained soil, it’s important that the water drains well in the area you are planting.  Plant directly in a garden area that has basic top soil.  Amend your soil with a 4″ layer of compost or bagged steer manure on the garden bed, and till or work into the soil with a pitchfork.  Only 4″ layer, too much compost will create leafy, leggy dahlias with not a lot of bloom.

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 or more of sun per day.  Morning sun/afternoon shade works best in warmer climates.  We do not recommend starting dahlias early in pots.  They do best when they are planted directly into the garden soil, when it’s the correct planting time in your area.

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 Field – North Bend

How long does it take after planting for the sprout to appear?

It takes up to 5 weeks for the sprout to appear above the soil line.

Watering

Your dahlias need moisture in the soil to start growing, moist but not saturated.  Normal springtime rain will give the moisture the tubers need.  If you live in an extremely dry climate, moisture needs to be added.  In dry climates, water weekly and don’t let the soil completely dry out, they need some moisture to start growing.  Keep the soil more on the dry side, with moisture.  If your soil has plenty of moisture and you’ve had rains recently, don’t add extra water. Dahlia tubers are susceptible to rot after planting, especially in soggy, wet soils.  When you see the sprout above the soil, deep soak 2-3 times per week.

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 – pH – Micronutrients

Feed at least 2 times during the growing season, one time with an organic, slow release fertilizer when you plant.  The next application of a 5-10-10 granular fertilizer, 30-45 days later OR you can apply another application of the organic fertilizer you used when you planted.  Organics also have many of the micro nutrients the dahlias need.  Compost also has nutrients and will also be feeding your dahlias during the growing season.  Add a 4″ layer of compost to the garden bed and mix in before you plant.

   Additional fertilizers:  Epsom Salt and Iron is good to add to your soil, IF the organic fertilizer does not have these nutrients.  If your soil is low in these nutrients, your dahlias will have a tendency to have yellowing in the veins or yellow leaves.

   Soil pH – test your soil to determine your soil pH.  Dahlias like a pH level of around 6.5 slighly acidic pH levels.  Add lime to correct the soil pH if you find the pH is too high or too low.  If the pH is off balance, it will effect how well your plants can absorb the fertilizer you are applying.  Look for a pH level of around 6.5, slightly acidic.  Lime can take months to dissolve and adjust the soil.  If it’s early spring, add lime then.  If it’s late in the season, wait until fall to add lime, then test again in the spring.  Once your soil pH is right, adding lime every 2-3 years will keep the soil at balanced pH levels.

Weed Control

Hand weeding is the only type of weed control you should use.

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.  Use Sluggo Plus or other slug baits especially as your dahlias are emerging from the soil.  Once your dahlias are around 12″ tall, slug bait is not totally necessary unless you notice a problem with them.

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.  Sluggo Plus will also help with earwigs and other insects.

Pinching & Staking your Dahlias

Pinching 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.  Planting in a row will make staking easy, use 2 T-Posts at the end of each row, then run 2 or 3 strings of twine to surround and support the plants as they grow.

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

At the first sign of any fungus, spraying with any over the counter fungicide every 7-10 days, until the fungus is under control.  We recommend Neem oil*, derived from the ‘Neem Tree’, it’s 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, big box or farm stores.

Digging Dahlias

Wait until your dahlias look like this before digging !!

WAIT FOR YOUR DAHLIAS TO FREEZE IN THE FALL !!  The cold temperatures tells the dahlias, “ok it’s time to go to sleep for the winter.”  The skins thicken up underground and they are better prepared to store for winter.  Wait at least 1-2 weeks after a freeze, before you dig them up.  Wait until the foliage has turned black and have completely died back. Leave them intact and don’t cut them down.  Dahlias have hollow stalks, cutting them down will allow water to get into the stalks, freeze and refreeze and potentially harming the tubers.   Dahlias dug too early will not store well over winter. After the foliage has died back and you’re ready to dig, 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.  Do not rinse your dahlias, doing so will cause them to shrivel in winter storage.  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:

View 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.  Wet tubers will rot over winter.

 Storage options are:

1. Store in clump form or divided loose in 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.