The Best Soil For Dahlias (Tips For Growing Great Flowers)

Learn the secrets to the best soil for dahlias here!

Dahlia plants boast colorful flowers that love full sun and bloom all summer long. When planted in the right growing conditions, these vibrant bloomers will produce heaps of flowers up to first frost.

coral pink dahlia flower

But dahlia flowers need the right kind of soil in order to thrive. Luckily, we’re dishing the best soil secrets for planting dahlia tubers right here.

And as a bonus, we’ll help you how to trouble shoot less than ideal soil conditions.

Best Soil For Dahlias

The best soil for dahlia plants is well draining soil that is rich in organic matter. The soil should be fertile, which means it is easy to grow plants in and nutrient dense.

Dahlias also love moist soil that has great drainage. Dahlia plants need soil that is rich in phosphorous in order to produce lots of new blooms. (Get our guide to the best fertilizer for dahlias here).

These popular flowers are heavy feeders, which means that they need nutrient dense soil in order to grow and produce those fantastic flowers.

If you have clay soil, you will need to add drainage and nutrients in order for dahlias to thrive. And if you have sandy, loose soil, you will need to add manure and compost to give the soil added nutrients and water retention.

Poor soil can limit new growth and stunt tubers as well as root, stem and flower development!  

Keep reading to learn even more tips on the best soil for dahlias. These dahlia growing tips will have you swimming in cut flowers by the end of summer!

Did you know? Pinching out the center of a dahlia plant when it is around 12 inches tall will encourage the plant produce lateral growth. The dahlia will become a bushier plant with a lot more blooms!  You can do this easily with a sharp knife or small pair of garden pruners.

How Native Habitat Of Dahlias Affects Their Soil Needs

Dahlias are native to the warm mountainous climates of Mexico and Central America. Days are warm and night temperatures hover around 65 degrees.

Dahlias are used to growing in rich and well draining warm soil. They are adaptable to many climates, but they thrive as perennials in areas and soils that are similar to their native habitat.

(They can still be grown as a tender perennial in cooler climates…read more here.)

There are thousands of different dahlia varieties, and their blooms range from petite colorful balls to bodacious dinner plate dahlias. Get our complete guide to growing dahlias here.

Learn about our favorite dinner plate dahlias, Cafe Au Lait, here.

3 Qualities Your Soil Needs To Grow Dahlias

In order to thrive, dahlia flowers need fertile, well draining soil full of organic matter. And the soil needs to be warm in order for the plants to thrive!

Dahlia flowers need soil that has these qualities

Nutrient Rich Soil:

Dahlias need a nutrient rich soil in which to thrive. The best soil for dahlia flowers is full of phosphorous and potassium and does not contain as much nitrogen.

The phosphorous in the soil will help help dahlia tubers to develop a healthy root system, and encourage the plant to produce more blooms. Without enough of this essential nutrient the plant will produce fewer flowers and smaller flowers.

Well Draining Soil:

Dahlia tubers need porous soil that will not hold excess moisture.

Heavy soil holds water and will encourage root rot in dahlia tubers. It will also make it harder for the plant to grow. If you have a thick, clay soil, you will need to amend it and make it more porous.

Warm Soil:

Lastly, dahlias need warm soil in which to thrive. Choose a warm spot in at least 6 hours of direct sunlight for your dahlia to grow. Morning sunlight with late afternoon shade is ideal.

Do not plant dahlia flowers until the soil is warm.

The time for planting dahlia tubers will range from early spring to early summer depending on your zone.  (Spring rains can also cause dahlia tubers to rot, so planting tubers when the climate has dried up a bit is a great idea!).

orange dahlia flowers

Dahlia tubers will not thrive in cold soil. (Dahlias can be wintered over in warmer climates but must be pulled from the ground and protected from frost in colder areas). Make sure when planting dahlia tubers that all danger of frost has passed.

Not sure what growing zone you live in? Visit this USDA hardiness map here.

Soil For Dahlias In Pots + Containers

Dahlias grown in pots and containers need a well draining, nutrient dense potting soil. We have used Miracle Gro with good results. Perlite and bark mixed into the potting soil helps with drainage.

The potting soil can be blended with compost for added nutrients.

You should not use soil from the vegetable garden or flower beds as it will compact in the container.  Plastic pots, ceramic and terra cotta can all be used with good results.

Always make sure the container you choose has drainage holes in the bottom of the pot. This will prevent too much water from building up within the roots, causing root rot.

Soil PH For Dahlias

Dahlias enjoy a slight acidic soil pH of 6.5-7.  According to the American Dahlia Society, soil in this pH range is perfect for the uptake of essential nutrients that the plant needs.  

You can test the acidity of your soil with an at home pH kit to get a good idea of your soil type.

Soil For Dahlias In Raised Beds

The best soil for dahlias in raised beds is rich, well draining and of a neutral to slightly acidic pH of 6.5-7. Amending soil in raised beds with compost is always a good idea.

Get our complete guide to growing flowers-for beginners-here!

Planting Time And Soil Temperature For Dahlia Tubers

Dahlias love warm soil, so the best time to plant a new tuber is well after the last frost date in late spring to early summer.  Dahlias grow very quickly and their tuberous roots will love the warm soil.

Wait until soil temperature is at least 60 degrees before planting dahlia tuber.

Signs Your Dahlia’s Soil Needs Improved

If a dahlia plant is not receiving the type of soil it needs, it will let you know. Here are some signs your dahlia plant is struggling:

  • Flower buds are small and stunted, plant is reluctant to push out more blooms
  • Plant is sickly looking and failing to grow healthy, lush foliage
  • Dahlia plant has yellowing leaves and the leaves are wilting

Best Fertilizers

The best fertilizer for dahlias is a phosphorous rich fertilizer with lower nitrogen levels. Look for an NPK ratio such as 5-10-10. This will encourage healthy root and bud development and lots of big, beautiful blooms.

Get more in depth information on fertilizing dahlias in our complete guide to dahlia fertilizers!

How To Amend Clay Soil

Heavy clay soil is not ideal for dahlia tubers, but sometimes it just can’t be avoided! In this case, you should heavily amend your soil to increase the drainage and nutrients available to your plant.

To amend clay soil for better drainage, add organic matter such as decaying leaf matter and organic compost to the soil. Composted steer manure will not only help with drainage but also fertilize the dahlia tubers. For added drainage, add peat moss to the soil.

And in very heavy clay soils, you may need to dig out the existing soil and replace with a high quality garden soil for your dahlias to thrive.

How To Amend Sandy Soil

While sandy soil may be well draining, it likely does not have enough nutrients to sustain the needs of a dahlia plant. Add in lots of organic matter to improve sandy soil. Make sure sandy soil has enough nutrients will result in the most beautiful flowers possible.

Use homemade compost, decayed leaf matter, and cow or steer manure (or a mixture of all!). Mix well into the soil.

Hot Climates and Soil Needs For Dahlias

Dahlias love warm climates and ideal temperatures for this plant are around 80 degrees during the day. Extended intense heat can stress dahlias and cause them to slow down flower production.

Giving a little attention to the soil can help dahlias survive hot temperatures. Mulching around the base of the plant can help insulate the roots from intense heat and keep in moisture.

Adding proper amounts of the right fertilizer regularly can also help the dahlias to survive hot temperatures.

And if you live in a hot climate, try to find a location where the plants will receive afternoon sun.

As always, make sure you have well-drained soil full of organic matter for your plants.

Planting Dahlia Tubers

Once you have your soil prepped and ready you can plant your dahlia tuber. Dig a hole about 5 inches deep (more or less, depending on the size of your tuber). To plant, place your dahlia tuber in the hole with eyes up and cover with a few inches of soil.

The same approach can be taken when planting dahlia tubers in pots or containers. Make sure to choose a container large enough to give tubers plenty of space to grow.

Learn how to grow snapdragons in pots and containers here.

General Dahlia Care

In addition to rich well draining soil, dahlias need regular watering and full sun. There are many dahlia varieties and tall plants will need support to hold up their heavy flower heads with either tomato cages or wooden stakes.

(Shorter varieties may not need staked and often do well in containers!).

Good light for dahlia plants is essential: Make sure your plants receive at least 6 hours of morning sun.  Afternoon shade is okay and may even benefit the dahlia plant!

Water plants about once a week in the early morning to prevent powdery mildew and disease. During dry periods you will need to water your dahlia plants more frequently.  Use insecticidal soap to keep spider mites and other pests at bay.  

Regularly remove old blooms (follow our deadheading tutorial here) for continued blooming. All varieties of dahlias will produce blooms until the end of the season! Dahlias also need good air circulation to prevent powdery mildew and other diseases.

Although there are many different varieties, they all have the same soil, light and watering needs!

For best results read more about dahlia care in our ultimate guide to growing dahlias here!

Are dahlias perennials and can you over winter them? That depends on the climate you are in!  Heavy rain can rot tubers, and in colder climates the freezing winter months will also kill the dahlia tubers.  Learn about growing dahlias as a perennial here

FAQ

What Is The Best Potting Soil For Dahlias?

Dahlias prefer a light but nutrient dense potting soil that allows for good drainage. Choose potting soils that feature some perlite or bark.  From here, mix the potting soil with some compost at the time of planting.  You can also add bone meal into the soil with the clump of tubers when you plant. This is the best way to ensure great soil for your potted dahlia. 

Do dahlias grow better in pots or in the ground?

Dahlias can grow great in pots or in the ground, but each growing approach has it’s advantages. Dahlias grown in pots can be easily over wintered by setting it in a shed or garage during the cold winter months. Container grown dahlias will need to be watered more. Growing dahlias in the ground gives you more options for larger dahlia varieties!

How Acidic Should Dahlia Soil Be?

Dahlia soil should be in the pH range of 6.5-7. This is the optimal range for nutrient uptake and will keep your dahlia plants healthy and strong.

You can purchase dahlia tubers from Swan Island Dahlias here!

pink and white dahlia tubers

Final Thoughts

Dahlias plants are happiest when grown in the right soil.  They can produce hundreds of blooms and will flower up until late autumn when given ideal soil conditions!

(There is nothing like seeing a beautiful dahlia bloom kiss cool air of early autumn!)

Dahlias love a nutrient dense soil that is rich in phosphorous and potassium. They need a loose, well draining soil to prevent root rot and plant decay.

Dahlias also love warm soil and need a sunny spot to grow in. When growing in pots and containers, purchase a container specific potting soil that is rich in organic matter.

Dahlias are a beautiful plant that will produce hundreds of flowers each growing season if you keep them happy. We hope this guide helps you create a healthy growing environment for your dahlias. May your heart-and your home-overflow with beautiful dahlia blooms this coming season!

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