Dahlia Planting Guide

Nothing is challenging about cultivating dahlias. They take little maintenance and produce large, multicolored flowers for months. In this article, we’ve got you covered whether you’re planting dahlias, pinching, staking, or harvesting.

Dahlias thrive in nutrient-rich, well-drained soil. They grow in mostly sunny conditions but prefer a shaded location. Dahlias have fragile tubes and cannot withstand freezing. They are planted outside in late May or June once the danger of frost has gone, and require a sunny location.

Dahlias, which come in various hues, sizes, and shapes, illuminate sunny borders throughout the summer and into late October. Smaller varieties can be grown in pots suited to most garden designs, from tropical to cottage. So let’s find out how to plant dahlias the right way!

When is the Best Time to Plant Dahlias?

Adele hardening off her dahlia plants

Temperatures below 60 degrees Fahrenheit are too chilly for Dahlias. However, the best time to plant dahlias is when the soil temperature hits 60 degrees Fahrenheit (15 degrees Celsius). A decent technique is to plant dahlias a few days after planting tomatoes in the ground.

To gain a good start on the season, some gardeners start tubers in containers a month in advance. Dahlias of medium to small size can thrive in containers.

There is a wide range in the amount of time it takes to plant a seed. Dahlias are commonly grown in the early spring. First, you must know when dahlias may be safely planted outside. After the risk of cold has passed in each growing zone, planting can begin.

Dahlia tubers should not be planted until the earth has warmed and all dangers of frost have passed, despite the allure of beginning your dahlia garden early. Generally, dahlia tubers can be planted outside from mid-April through May in most places.

Different Types Of Dahlias

Our current dahlias derive from a single wildflower that grows in Mexico. Although Dahlias are usually classified based on their blooms’ diameter, they are also classified based on their petals’ development style and the overall shape of their flower heads.

According to the NDS, dahlias can currently be categorized into 15 distinct groupings. The following is a short list of the most popular varieties of dahlias.  

Single Dahlias

Height: 16-24″ tall

Petal rings around the central disc of single dahlias, such as the illustrated ‘Joe Swift’ and ‘Bishop of York,’ as shown. If the petals overlap, they might have different shapes and sizes. Species of pollinators are drawn to this variety of dahlia.

Cactus Dahlias

Height: up to 60″ tall

The flowers of cactus dahlias, including ‘Doris Day’ and ‘Ryecroft Pixie,’ are double, with petals that curve outward from the tip to the base. They range in size from miniature to enormous.

Anemone Dahlias

Height: 24 to 48″ tall

Anemones don’t have a disc in the middle of their flowers. Instead, a dense core cluster of tubular disc florets is surrounded by one ring or multiple rights of flat ray florets. This arrangement is more common. Dahlias with anemone flowers, such as Alpen Fury, Blue Bayou, and Garden Show, are common garden plants.

Collarette Dahlias

Height: 30 – 48″ tall

Dahlia variants with a distinctive outer ring of eight or more flat ray petals and an inner circle of disc petals are known as Collarette dahlia types. The collar—an inner ring of smaller ray florets—makes this group special. This type includes Bumble Rumble, Christmas Carol, and Clair de Lune.

Waterlily Dahlias

Height: up to 48″ tall

Floral ray florets of the waterlily dahlia vary in shape but are usually straight or slightly unusual along their length. This gives the blossom an illusion of shallowness. In this classification, popular types include Anna Lindh (White), Sascha (Yellow), and Rancho (Orange).

How to Plant Dahlias?

Plant a solid stake in the ground before planting a dahlia, as most dahlias require stakes. However, ensure you don’t damage the plant’s tuber or root system if you use a stake after the plant has grown. Staking tomato plants using tomato cages is another option.

  • The eye (similar to a potato sprout) on the tuber should be pointing up when it is placed in a hole several inches deep. Plants grow from tubers with eyes on their shoulders (or crowns).
  • The spacing between dahlias should be at least 2 feet apart if you are planting a large number of them in the same area.
  • Plants produced from tubers should be placed at the same height as in their container. The top of tubers should be near the soil surface, where shoots develop. It’s best to keep plants at least 60cm apart.
  • If you are using cuttings that have been rooted in pots, place them in the ground a few millimeters lower than where they were before. Plants should be spaced between 20in and 2ft apart.
  • Ensure the soil is well-watered before applying a thick layer of mulch around the base of the stems. You can buy a watering can such as Bloem Easy Pour Watering Can (on Amazon) to water your beans regularly.

Overwintering Dahlias

It’s time to start thinking about how to overwinter dahlias now that the first frost has arrived. When the temperature drops and the frost comes, dahlias will remain to bloom with their lovely blooms for as long as possible.

Unfortunately, flowers, buds, and foliage remaining after this stage will all die off simultaneously. Consequently, it’s time to start safeguarding your dahlias from the winter weather so they can grow again next year.

  • Dahlias will die if they are left in the garden over the winter if the weather is extremely cold or damp.
  • As a result, the tubers should be lifted after the foliage has become black from cold.
  • Using a garden fork, gently pull the tuber and remove the soil. Cut the stems back to around 12 cm.
  • To dry out the tubers, place them upside down in a newspaper-lined tray in a dry place for a few weeks.
  • A shallow tray of dry compost or horticultural sand can be used to keep the tubers cool and frost-free.

Maintaining Dahlias

It is vital to keep dahlias weed-free. To keep weeds away and preserve water, mulch the plants with organic material. When the plant reaches a height of 15 inches (38 cm), pinch back the terminal buds to encourage healthy branching and budding.


Dahlias need around six to eight hours of direct sunlight each day to bloom. When the sun is at its hottest, this plant does best in the shade during the mid-afternoon in climes more like their natural one.


These flowers prefer well-draining, nutrient-rich soil that is rich in organic matter. Make sure your garden soil isn’t too dense by adding sand, peat moss, or manure to lighten it up.

Soil with a neutral pH of around 6.5 is ideal for Dahlias to thrive. You can buy a soil pH measuring meter like Luster Leaf 1880 Rapitest Tester (on Amazon) to ensure that soil pH is optimal.


Dahlias thrive when the soil temperature is just right. Therefore, ensure the soil temperature is at least 60 degrees Fahrenheit when planting these flowers (you can check with a metal thermometer). Make sure to delay until spring or early summer to grow dahlias because they struggle in cold soil (less than 50°F).


If you have pets, you should keep dahlias away from them because they can produce uncomfortable symptoms like vomiting and diarrhea, even though they aren’t highly harmful to pets. If you have a pet, be careful where you put your dahlias if you plan on planting them in the garden or displaying them in a vase.


Once the pH and specific soil needs have been determined, it is advisable to begin fertilizing by doing a soil test. If you don’t have such information, you should regularly use a water-soluble or granular fertilizer to get the best results.

When it comes to dahlias, conventional knowledge says to use a high nitrogen fertilizer in the middle of the season and a low nitrogen fertilizer at the end.

Common Pests and Prevention

Dahlias are a favorite food source for many pest insects. Caterpillars and larvae are also a problem, but sucking insects are likely to be the most prominent problem.

  • Aphids
  • Thrips
  • Mites
  • Leafhoppers

This is despite the fact these pests are so tiny that their habit of sucking sap from the plant can have a detrimental effect on its health and possibly spread illness. To lessen their impact, use horticultural soap or a burst of water from a hose. Dahlia flower pests include several forms of borers.

Early season application of systemic fertilizers may provide some protection. However, cutworms, slugs, and snails cause visible surface damage to plants, reducing their health and aesthetic appeal.

Nighttime hunting can eradicate cutworms with a flashlight and the squish pest management approach. With diatomaceous earth or slug bait, slugs and snails can be managed.

If you detect silvery slug and snail trails, limit mulch depth to no more than 3 inches (8 cm). And you can buy slug bait like Corry’s Slug & Snail Killer (on Amazon) to eliminate slugs disturbing your bush bean.

Your dahlias will flourish if you keep the weeds-free area surrounding them. Pruning any damaged areas of the plant is necessary.

Harvesting Dahlias

Green plants with orange and yellow flowers in field

Your Dahlias will bloom abundantly until the first frost. Therefore, dahlias should be taken when they are open before the back petals have dried up. After harvesting the dahlias, we place them in clean water containing a transport/holding solution before placing them in the chiller.

Flower yields vary by variety and depend on soil nutrients, management (pinching, deadheading, etc.), planting date, growing zone, and exposure to sunlight. A healthy dahlia plant can typically yield 10 to 20 flowers per season.

Using a pair of clippers, gather dahlias in the early morning before the day’s heat sets in. Untreated water should be cut right into the water. Next, cut stems forcefully by slicing deeply into the plant right above a leaf node or growth point, leaving stems between 18″ and 24″ long (or proportionately less if the plant is shorter).

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