Skip to Content

When To Plant Dahlia Tubers for Blooms All Summer Long

When To Plant Dahlia Tubers for Blooms All Summer Long

Although dahlias are known for their long-lasting blooms, it is important to plant the tubers at the right time in order to ensure a continuous display throughout the entire summer season.

If you miss that small window, your dahlias might not bloom that year or will only have a few flowers here and there. 

Can I plant dahlias tubers in July? Waiting until July to plant dahlias is too late for the plants to grow and bloom. If you have a short growing season and the last frost is late, start the dahlia tubers indoors and transplant them when the weather improves and the soil becomes workable. 

The right time to plant dahlia tubers depends on your specific microclimate and the date of the last frost in your Zone among other factors.

Read more to find out when to plant dahlias and get a long bloom season.

When To Plant Dahlia Tubers

When it comes to planting dahlia tubers, you should factor in the air and soil temperatures as well as other unpredictable weather conditions such as sudden snowstorms.

You need to know the exact dates of the last frost, and then decide on the right time to plant the tubers.

Best Time To Plant Dahlia Tubers

Growing Zones and the last frost dates aside, the best time to plant dahlia tubers is usually between mid-April and mid-May.

This gives you a lot of leeway to choose the right time in your specific zone. It also gives the dahlia tuber enough time to grow and establish before producing flowers. 

Last Frost Dates

Every Growing Zone in the USA has a last frost date. This date changes from one year to the next, but getting a general idea of the average last frost date in your Grow Zone helps you choose the right time to plant your dahlias.

Ideal Ground Temperature for Planting Dahlias

The roots of the dahlia are not only sensitive to the soil temperature, but they’re also shallow. They grow about 2 inches under the surface. That means that both the air temperature and soil temperature will affect the roots.

You should wait until the soil temperature is above 60 degrees Fahrenheit before planting your tubers.

Is July Too Late To Plant Dahlias?

The latest you can plant dahlia tubers is in June, and that’s in cold zones where the last frost lingers until early June.

Waiting until July to plant your dahlia is quite late. There’s little chance the plant will grow and establish in the small window between midsummer and the first frost.

What Happens if I Plant Dahlia Tubers in July?

If you plant dahlia tubers in July, the plant will not have enough time to grow and produce blooms.

Before the buds open, the first frost will set in, and the plant will go dormant. Most of the buds will die, and you’ll have to wait until the next season to get any flowers.

Where To Plant Dahlias

A dahlia plant with loads of red-and-white flowers.

Choose a sunny site for your dahlias. Wait until the threat of the last frost is over before planting them.

If you want to get a head start and enjoy a long bloom season, start the tubers indoors and transplant them when the soil temperature goes above 60℉.

Dahlia Light Requirements

Dahlias enjoy full sun and need between 6 and 8 hours every day of full sun during the growing season.

Choose a site facing the south or west in cold to warm zones. In hot zones, select a site facing the north or east to protect the dahlias against the hot afternoon sun.

Best Soil for Dahlias

The best soil for dahlias is well-draining, rich soil. Loamy soil fits the bill since it’s not compact and doesn’t lose moisture quickly but doesn’t retain it for too long like clay soil either.

Amend the soil to bring the pH levels to 5.5 to 6.5.

Dahlia Tuber Spacing

When planting more than one dahlia tuber in the garden, make sure to space them out to allow the plants to grow without competing over resources.

On average, space the tubers 12 to 18 inches apart in every direction. This will also improve the ventilation between the plants and prevent fungal infections and bacterial diseases.

How Deep To Plant Dahlia Tubers

If you’re planting a single dahlia tuber, place it in the hole 4 to 6 inches deep with the root end facing down and the neck with the eyes facing up.

Sometimes it’s not easy to tell which end is the neck. In that case, place it on its side 3 to 4 inches deep, and cover it with soil.

If you’re planting a cluster of tubers, plant them in the hole, and keep the old neck level to the surface of the soil.

How To Plant Dahlia Tubers

When planting dahlia tubers, timing is crucial for the success of the plant, but you also need to consider other factors such as the soil, the location, the pH levels, and the nutrients in the soil.

Here’s a step-by-step guide to planting dahlia tubers:

  1. Check the dahlia tuber before planting it. Make sure the neck is intact and that it has between 4 and 5 eyes.
  2. After the threat of the last frost is over and the soil temperature rises to 60℉, choose a sunny site for the dahlias. Make sure the site gets between 6 and 8 hours of sunlight every day.
  3. Clear any debris and weeds, and turn the top 10 inches of the soil.
  4. Add in plenty of organic compost and bone meal, and mix it well into the soil.
  5. Dig a hole between 4 and 6 inches, and plant the tuber with its neck pointing up.
  6. Cover the hole with soil, and pack it with your hand to push out air pockets.
  7. Water the tuber to help the soil settle. 
  8. When the tuber sprouts, water it regularly to keep the soil evenly moist. 

Related Questions:

Can Dahlias Get Too Much Sun?

In hot zones where the summer sun can get too intense, the dahlia plant will struggle with the excessive heat and scorching sun.

High temperatures can impact the growth of the plant and prevent it from flowering. Consider providing your dahlias with partial shade in the hot afternoons. 

Can You Grow Dahlias From Seed?

You can grow dahlias from seed, but it usually takes months for the seeds to germinate and sprout into seedlings ready to transplant into the garden.

If you want to start dahlias from seeds, start the seeds indoors in late winter or early spring and transplant them in May.

Conclusion

The best time to plant dahlia tubers is between mid-April and mid-May. This gives the dahlia enough time to establish and develop full foliage and then send out its blooms from midsummer until the fall.

If you delay planting the dahlia tubers until after June, there’s a chance you won’t get blooms that season.