Dahlia Growing Guide

Dahlias are incredibly beautiful flowers that bloom during midsummer through early autumn in a variety of colors and sizes. Anthophiles or plantspersons would find it difficult to imagine summertime without the various shapes, colors, and sizes of blooming dahlias.

These flowers are a close relative of sunflowers and daisies and are quite easy to grow. Many experts will tell you that if you can grow tomatoes in your garden, then you can grow dahlias as well. As easy as it is to grow dahlias, you first have to learn how and when to plant and grow them.

Today we will discuss exactly that and help you learn how to grow dahlias with our dahlia growing guide.

But first…

What Is Dahlia?

Dahlia is a flowering plant and a member of the Asteraceae family of plants, making it a relative of aster, chrysanthemum, daisy, sunflower, and zinnia. The dahlia flower symbolizes elegance, wealth, involvement, and love in many cultures.

The Aztecs used dahlia as food and in various ceremonies, as it symbolized religion for them. For the modern garden, dahlias can be a gorgeous addition that ranges in sizes from 2 to 15 inches and typically grows to be 4 or 5 feet tall but can grow as high as 8 feet.

Dahlias have a growing season of 4 months and can brighten or spruce up any sunny garden. They are best suited to moderately warm and moist climates, and they do not fare well in extreme temperatures like frost or heat from long summers.

This is why they don’t survive in the long summers and tropical weather of lower south states like Texas and Florida, where the heat can wilt them. While they will bloom in most soils, northwest coastal states provide an ideal sunny climate and temperature.

Larger blooms tend to be more sensitive to heat and will not bloom in high temperatures above 90. Dahlias are hardy, easy-to-grow perennial plants that do not require special care in warm zones 8-10, but they do not survive colder zones 3-5, so you may need to move them indoors before the first frost.

You can check what hardiness zone you are in and your state’s specific plant hardiness using this USDA  Plant Hardiness Zone Map. Currently, the majority of commercial dahlias in the US are grown in Washington and Oregon.

Types of Dahlias

There are 42 species of dahlias with plenty of hybrids that are commonly used as garden plants. The flower forms can vary in color, size, and shape. Typically, dahlias are classified by various factors, including the diameter of bloom, the style of petal growth, the shape of the flower head, etc.

While there are plenty of dahlias, here are some of the most common, most sought-after, and most rare groups or types of dahlias.

Decorative Dahlia

This group of dahlias includes larger varieties like a dinner plate and semi-dinner plate dahlias. The blooms are large, often 12-15 inches and the plant are also tall.

Cactus Dahlia

Fully double with pointed tubular petals, cactus dahlias bloom similar to cactus flowers and are very tall. There are some impressive color combinations in this group of dahlias, and they appear starburst due to the flower head arrangement.

Semi-Cactus Dahlia

Semi-cactus dahlias lack the complete pointed and tubular petals of cactus dahlias. However, they are better at maintaining form through harsher winters. They are also very tall and can grow up to 5 or 6 feet.

Pompon Dahlia

One of the most popular dahlias, pompon dahlias, have spherical flower heads that are perfectly rounded. They are mid-height dahlias with smaller flowers that are often seen in bridal handheld bouquets.

Ball Dahlia

As you would expect, the flower shape of the ball dahlia is spherical with curved petals. These are mid-sized dahlias that resemble large, double zinnias but are more vibrant.

Waterlily Dahlia

One of the most gorgeous flowers, the waterlily dahlia, has larger, waterlily-like blooms. They are mid-height, fully double dahlias with rounded, broad petals.

Single Flowering Dahlia

These are smaller, less common, and rare-to-find dahlias, but they are perhaps the oldest type of dahlia. They resemble daisies but are much larger.

Of course, there are plenty more types of dahlias like the peony flowering dahlia, collarette dahlia, topmix dahlia, mignon dahlia, and more. The most popular choices of dahlias include varieties such as Kidd’s Climax, Miss Rose Fletcher, Bishop of Llandaff, Jersey’s Beauty, and Bonne Esperance or Good Hope dahlias. You will most likely find these varieties in your local nursery.

Choosing a dahlia for planting can sometimes be a tough choice because there are so many colors and sizes to choose from. However, once you know what varieties you want, you’ll need to know how to plant and grow them.

Dahlia Growing Guide

When it comes to planting and growing dahlias, you’ll have a much easier time than with most other flowering plants. This is why so many professional and amateur gardeners prefer dahlias. The ideal place in your garden is where the dahlia can get 6 to 8 hours of direct sunlight.

Morning sunlight is preferred over evening sunlight, but you need to make sure that the dahlia is protected from strong winds because tall dahlias will bend and break if they are not supported. It is always best to consider the dahlia’s size at maturity before you plant it.

Dahlias are not fussy about soil, but ideally, you want rich, moist, fertile, and well-drained soil with wind protection and plenty of sunlight. Soil with pH levels between 6.0 and 7.5 is best. If you have heavy clay soil in your garden, you can enrich it with organic matter, compost, or rotted manure to relax and ease the soil for improved drainage.

When Is the Best Time to Plant Dahlias?

Since dahlias cannot survive frost or cold soil, you should ideally plant them when the soil is at least 60 degrees Fahrenheit, so there is no danger of frost. For most people, it is recommended that you give the dahlia a head start indoors in containers around 4-6 weeks before you plant them outside.

This provides enough time for the soil to warm up after the last frost. As a rule of thumb, dahlias are planted outdoors a few days after you would plant tomatoes in late spring. However, if this time is passed late May or early June in your zone, it is best to start growing your dahlias indoors 4-6 weeks prior to the last frost.

Indoor Planting in Containers

You can use 12 x 12 containers for planting dahlia tubers indoors. The dahlia tubers look like tiny brown carrots and you can lay them in a container with their stem facing up. Cover the dahlia tuber with around 1-3 inches of fertile soil and wait till you see new growth through the water.

It is important to note, however, that you should only plant small to mid-sized dahlias (under 4-feet tall) in containers, especially if you want to leave them in the containers. Make sure to avoid tubers that appear wrinkled because this is a sign of rotting.

Planting Dahlias Outdoors

When planting dahlias outdoors, you want to pick a spot with plenty of sunlight and rich, well-drained soil. Soil prep can often be the key to quick and healthy dahlia growth.

Enrich the soil with aged manure or compost and add good quality organic fertilizer, although you can skip the fertilizer as well. When planting dahlias, it is recommended to dig around 6 to 8-inches deep. However, soil prep requires you to dig around 8 to 10-inches deep to loosen the soil and improve drainage before planting.

Depending on the size and variety of dahlia you want to plant, you will need to adjust depth and spacing. Large dahlias and dahlias grown for cut flowers require a dedicated plot where they aren’t competing with other plants.

These dahlia tubers should be placed 3 feet apart, but if you want dahlias to support each other and make for a good flowering hedge, you can space them around 1 foot apart. Short to medium height dahlias (under 4 feet tall) are typically planted 2 feet apart from other summer flowers.

Compact dahlia varieties can be planted much closer, around 9-inches apart. Make sure you plant the tubers with the “eyes” or growth points facing upwards. You can cover the dahlia tubers with 1-3 inches of soil, and as it sprouts, you can fill the soil up to ground level.

One important thing to note is that you shouldn’t water the tubers immediately after planting because this can cause rotting. The best time to start watering is when the sprouts start appearing over the soil.

When planting larger dahlia varieties (4 feet or taller), staking is highly recommended when you plant. This prevents rain, wind, or even the weight of the dahlia flowers from breaking the brittle stems of the plant.

You can place the stakes when you plant the dahlias or after they have sprouted and grown in. The stakes provide good support that allows large dahlias to thrive and grow better.

Growing Dahlias

Regular watering is important for the healthy growth of dahlias. However, you must be careful not to overwater because soggy soil can result in rot. Deep watering that keeps the foliage dry is recommended during the initial growth period.

During mid-July, around 8 weeks after you plant your dahlias, they should start to bloom. Once the dahlias are established, you should water them 2 to 3 times a week or more if the climate in your region is hot and dry.

You must also tend to your dahlias after rainfall because the open blooms typically fill up with water, which can lead to heavy flowers that break the brittle stems. It is also ideal to occasionally introduce low-nitrogen liquid fertilizer after sprouting and every 4 weeks until early autumn.

Avoid over-fertilizing with nitrogen as this can cause rot or a lack of blooms. Similarly, most dahlias do not require mulching because dahlias prefer sunlight on their roots. The soil remains warm, and the foliage remains dry. However, in very hot or dry regions, mulching may help retain healthy moisture levels.

Large dahlia flowers can also benefit from disbudding. If you remove the smaller buds around the central bud in a cluster, more energy will go to the growth and blooming of the central dahlia. This typically results in fewer but significantly larger blooms.

It is also important to deadhead fading flowers for a larger number of blooms. The combination of soil prep, staking, moderate pinching, disbudding, and deadheading offers incredible results with larger dahlias, and you can expect grand displays for three or more months.

On the other hand, smaller bedding dahlias do not require disbudding or staking. However, they can become bushier if you find the center, shoot above the third set of leaves, and pinch it out.

Winters and Storing Dahlia Tubers

In hardy zones like zone 8 or higher, dahlia plants can simply be cut and left to overwinter with mulching, but they are prone to rotting. If the winters are harsher than usual, it is ideal to lift, store, and let the tubers hibernate in a cool, dry, and dark place.

In colder zones, the foliage dies almost instantly upon the first frost in the fall. If the winter climate is mild in zone 7 or 6, the dahlia plant may survive the winter. If not, it is highly recommended to lift and store the roots for the winter.

A great tip is to cut the stems a couple of inches above the dahlia tubers, wash the dirt off, and let them dry in the sun before storing. Peat moss or sawdust in paper bags are ideal for storage, but you must avoid plastics as that can easily result in rot.

You’ll also notice that your tubers have increased in size since you first planted them, which means more dahlias tubers for you to plant in the coming spring. Just remember to label your stored dahlia tubers according to their color, size, and/or variety, so you know which is which next spring. This is important because all dahlia tubers look the same, regardless of the color or variety of dahlia.

Conclusion

Dahlias are gorgeous summer plants that look incredible in any summer garden. The convenient planting and growing make them one of the best flowering plants to add to your garden. Following our dahlia growing guide, you should have no trouble choosing, planting, growing, and storing a wide range of dahlia plants for your garden. If you want to learn more about our dahlia growing guide, different varieties of dahlias, or the best growing guides for other plants and flowers, please visit our website today.