Guide to Growing Black Dahlia Flowers

Last Updated on April 9, 2024 by Real Men Sow

Black dahlia flowers are a member of the Asteraceae Family. These perennial plants can be grown in warm climates from underground tubers. The tubers are sown with green, vegetative shoots in spring. Over time, many layers of branching shoots develop. They are then covered with bobbed flowers.

Their height varies due to the fact that there are many varieties and species of black dahlias. They can grow to three or five feet tall. These flowers may be called black but they aren’t really black. Some flowers are deep purple while others may appear black if they are given the right conditions.

Depending on the type of flower, shapes and sizes can also vary. They can grow up to one foot in size. They are classified according to their colour, flower appearance, size, and height.

Growing Black Dahlia Flowers

The Best Conditions to Grow Black Dahlia Flowers

Black Dahlia’s tubers can’t withstand very low temperatures. If winter is below freezing in your area, you might consider planting them in spring. Then, you can dig them in autumn. Plant them in the soil if possible. Don’t plant them until the soil reaches 60 degrees F.

You can also pre-sprout tubers indoors. This can be done between 4 and 6 weeks before you transplant them outside. This will help your black dahlia flowers bloom earlier. For indoor germination, you will need a shallow container filled with potting soil (a little wet). Place the containers in a warm place.

After a few weeks, the tubers will start to sprout. Before you transfer, wait until the outside conditions are favourable. Dahlias are long-flowering, and once they have established themselves, you’ll get flowers all through autumn up to the first frost.

Planting Black Dahlia Flowers

Certain dark dahlia flowers variety can reach 4 feet in height when grown under ideal outdoor conditions. They may grow up to 1 foot in a pot. Black dahlias are able to grow indoors as well as outdoors. 
However, they require a lot of energy because they have large blooms. They may not be able to bloom indoors if they don’t have enough light.

Before planting the tubers, wait until the soil has warmed up. Depending on the size of the tubers, you will need to dig holes about 4-6 inches deep. Follow the correct orientation. If you have pre-sprouted tubers, grow them facing up. If you have not pre-sprouted the tubers, locate a round eye to place in the hole. Cover the tubers with a good layer of soil.

Best Soil

Black dahlia flowers prefer soil that is rich and well-drained. To improve drainage, you can add compost. If the soil is very heavy, you should consider adding nutrients. It is possible to amend the soil by properly digging it before adding compost. It is important to prepare the soil for tubers.

Flowers need a pH between 6.0 and 7.0. This should be between 6.0 to 7.0. Add some elemental sulphur to soils with a lower pH. The pH can also be raised by adding garden lime.

Sunlight Exposure

Black dahlia flowers require a lot of energy to bloom. To ensure a long-flowering dahlia, you must plant them in an area with at least 8 hours of sunlight each day. They can tolerate a little shade. They will only produce a small number of flowers. Dahlias can’t grow large indoors.


Don’t water the tubers until they sprout. This can cause them to rot, especially in cooler soil. After the tubers sprout, water the soil once per week. Avoid dry, saturated soils. It is best to water infrequently and deeply.


Black dahlia flowers can grow well without any additional nutrients. They will be more happy if they are fertilised regularly. It is important to choose the right product. You should use fertilisers with more potassium and phosphorus than nitrogen. This will encourage better flowering. After moving the plants outside, fertilise the soil approximately one month later. Follow the instructions to the letter.


Black dahlia flowers can reach up to five feet in height. Staking may be more effective in maintaining the plants upright. To avoid damaging your tubers, you can insert the stake right after you plant them. You can also stake them every few feet. Either single stakes or cages can be used. You will still achieve great results regardless of which method you use.


By pinching your black dahlia flowers, you can get more flowers. Although it may delay the first flowering, this will increase the flower yield. Pinching, or topping, is the process of removing terminal buds that are less than 1 foot high. The plant should have four leaves. You can remove the bud with scissors or your hands, but not the leaves.


Real Men Sow
Real Men Sow

Hello, I’m Pete and I’m currently based in the west of Scotland, in a small place called Rosneath, where I’m exploring my garden adventures. I personally started gardening around 6 years ago and initially, I started out by growing my favorite fruits and berries, such as strawberries, Raspberries & Gooseberries. Since then I’ve added a lot of vegetables and working closely with my neighbor, it’s been a lot of fun.