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How To Grow Dahlias

By Ray Allen, Founder of American Meadows
 

If you've never grown a Dahlia, it's high time you did! Most gardeners can't grow just one, and there are endless varieties to keep you busy. Find helpful preparation and planting instructions, staking advice, tips for end-of-season tuber storage, and more. 

How To Prepare Your Soil For Planting Dahlias

Some plants can handle any growing condition, but Dahlias really need the right conditions to produce the outstanding blooms they’re known for. With a well-prepared soil bed, your Dahlias will create beautiful growth very quickly. Follow these steps for success! 

  • Dahlias prefer rich and well-drained soil. Loose, nutrient-rich soil will feed tubers and encourage strong root growth. Soil must be well-draining, because Dahlias like plenty of water, but soggy soil will cause tubers to rot. Dahlias are great for sandy, loamy, or acidic soil.
  • If you’re starting with clay soil, dry soil, or compacted soil, it will be important to make sure that you properly prepare your planting area in order to see growth and blooms. If you have challenging soil, or if you live in an area with heavy rainfall, you may want to consider growing Dahlias in berms or raised beds to create optimal conditions.
  • Enrich your soil with compost work in a good organic fertilizer before planting. Look for a fertilizer that’s low in nitrogen, to encourage blooms and not too much leafy growth. Organic material will feed your Dahlias, and help the soil to retain moisture as needed for the plants.
  • Dig at least 10 inches to 1 foot deep (or create a raised bed 10 inches to 1 foot deep) to loosen the soil and give tubers enough space to grow and to improve soil drainage. 

When To Plant Dahlias

Generally, we ship your Dahlia tubers at the right time to plant! Tender Dahlia tubers are generally planted outside around the same time you plant tomatoes.

If that’s not until late May or early June where you live, you can start dahlias indoors, 4-6 weeks before your last frost date. In containers, lay tubers on their sides with the stems up and cover with 2 inches of soil. Wait until you see new growth breaking through to water. Then, they can be transplanted outside when it’s warm enough.

How To Plant Dahlia Tubers

1. First, prepare your soil as outlined above. Don’t skip this step! Preparation is the key to success.

2. Dig holes for planting. 

  • Spacing will vary based on your varieties. Most Dahlias are spaced with approximately one tuber per square foot. The largest varieties of Dinner Plate Dahlias will do best with wider spacing, about 12-18 inches apart, to allow for foliage and flowers to grow. Compact varieties can be planted with multiple tubers per square foot. See the spacing recommendations on your package.
  • Holes should be relatively shallow and wide enough for tubers to be spread out, like fingers. Tubers for large varieties like Dinner Plate should be about 6 inches deep, while smaller varieties can be about 4 inches deep. 

3. Plant tubers.

  • Place tubers so that the crown (where the tubers connect) is a few inches below the surface of the soil. If there are buds, or ‘eyes’ on the tubers, place those facing up - that’s where stems will grow. 
  • Gently backfill soil around the tubers so that they are completely covered by a few inches of soil. There is typically some stem material at the top of the tubers, and if so, the stem can be at or just below the surface of the soil. 

3. Staking

  • For Dahlias with large flowers, and generally those growing 3 feet or taller, we recommend staking when you plant. See staking tips below.

4. Watering

  • Once planted, give tubers a thorough soak to remove any air pockets and encourage root growth. Until they sprout, Dahlia tubers don’t need much water. 

5. How long until they sprout?

  • Generally about 3 weeks - but it can take longer depending on the weather. Dahlias will sprout faster when the soil and surrounding climate are warmer, and they can be delayed or take longer when soil and weather are remaining cool. When planting in spring, and depending on your climate, they can be variable.

Continue reading for growth & care throughout the season!

See How To Plant Dahlias Step By Step

Tubers and a Wheelbarrow
After fear of last frost has passed, it's time to plant. Tubers from last summer are ready to go back into the ground.
Dahlia Planting Instructions 2
The soil for each hole is worked well, and since these are big dahlias, a stake is put into place early on.
Dahlia Planting Instructions 3
We're planting three clumps of tubers per hole. (Each will result in a large plant.)
Dahlia Planting Instructions 4
Our large dahlia garden is planted and fertilized. Now all we need is regular watering and a few weeks.
Sprouting Dahlias
About two weeks after planting, the beautiful foliage is up and growing.
First Dahlia Buds of the Season
Soon after the foliage appears, buds follow. They're small now, but will soon expand into bloom.
Beginning of Bloom Season
By mid-summer, plants are about 2 1/2 feet tall, and first flowers are open. Buds are everywhere!
Dahlias in Full Bloom after a few weeks
A few weeks later, plants are full grown at about 4 feet, and all this color will continue until frost.

How To Stake Dahlias

If you're growing big Dahlia plants, staking will be important. We recommend being pro-active, and setting up your stakes when you plant your Dahlia tubers. The beautiful foliage grows on somewhat brittle stems, and heavy rain, wind, or even the weight of the flowers once they've opened can break the plant. You don't want that to happen, especially at bloom time!

  • Set one or two stout stakes beside each tuber after you plant them.
  • Wooden stakes can be buried or hammered in. Metal stakes can be placed in the soil more easily and are a great option if you find that your Dahlias need a little extra support after they've grown in. 
  • Have the twine or 'twist-ems' ready to support the stems as they grow.

With a little effort, the stakes will be completely hidden by the leaves, but you will thank yourself when your big, beautiful flowers a growing with support.

staking dahlia tubers at planting time
Stakes can be placed at planting time.
staking dahlias plants before they bloom
Or, stakes can be placed after plants have grown in.

Growing & Care For Dahlias Throughout The Season

 Growth Habit

Dahlias grow quickly, producing bush plants and flowering in the first season. 

Watering Dahlias

Water regularly, and try to keep your foliage dry. Avoid overwatering, as soggy soil can lead to rotting tubers. We recommend less frequent, but deep watering. 

It’s best to let the soil dry out between watering, as soggy soil can easily cause tubers to rot (remember - that’s why good soil preparation is so important). Water thoroughly about once per week until Dahlias sprout. 

Once you see top growth, water as needed when soil has dried out. As the plant starts to grow and temperatures increase with the start of summer, you may need to water more often. If you’re experiencing regular rainfall, you may not need to water if your soil is not drying out. 

When watering, keep water near the soil surface, and avoid getting leaves wet to help prevent diseases. Water slowly and deeply to give the soil a thorough soak.

Fertilizing Dahlias

Look for a fertilizer that is high in potassium (K) and phosphorus (P) but low in nitrogen (N). Potassium and Phosporous encourage bud growth and flowering.  to prevent leafy bushes with few blooms. Check your NPK (Nitrogen-Phosporous-Potassium) levels in your fertilizer before you purchase. Expert growers recommend formulas such as 5-10-10, 10-20-20, or even 0-0-10. Fertilizing dahlias just a couple of times can make a big difference to the flower yield. Add when planting, and once a month at most before flowering begins. 

Mulching Dahlias

In very hot, dry areas, you may want to mulch to help retain moisture, but in most areas, we recommend skipping mulch so that the soil can stay warmer and foliage can stay dry.

End Of Season Dahlia Care & Tuber Storage

In the right conditions, Dahlias can overwinter in the garden in zones 8-11. They need well-drained soil and dislike wet winters. In colder zones with winter frost and freeze, Dahlias won't survive after frost.

Some gardeners will treat Dahlias as annuals, re-planting new tubers each spring. You can also dig up your tubers and store them for the winter in a cool, dry, dark place, then re-plant them the following spring.

For more detail on storing dahlia tubers, Learn More: How To Dig and Store Dahlias For The Season

Ready To Dig In? Shop Dahlias For Spring Planting

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