How to Grow Dahlias: Your Complete Guide

Growing dahlias (Dahlia) is a rewarding and enjoyable undertaking for gardeners of every skill level. With their stunning array of colors, shapes, and sizes, dahlias can add a touch of beauty and elegance to any garden or landscape. From the moment they start to sprout until the time they bloom, dahlias require care and attention, but the end result is always worth it. Whether you’re a seasoned gardener or a novice, growing dahlias can be a satisfying and fulfilling hobby. Keep reading to learn the finer points of growing head-turning, traffic-stopping dahlias!

How to Grow Dahlias: Annuals or Perennials?

Dahlias are native to Mexico and Central America where they are considered perennials. They prefer warm temperatures and will not grow well in areas with extended periods of cold weather or frost. While they can tolerate some heat, in hot climates it’s important to provide adequate watering and some afternoon shade to prevent the plants from becoming too stressed by the heat. Overall, dahlias prefer a balance of warm temperatures, ample sunshine, and moderate moisture levels to thrive.

In the U.S., dahlias are usually grown as annuals, though they are classified as tender perennials. Dahlias can be grown as perennials in USDA Hardiness Zones 8-11, where the winter temperatures are mild enough to allow the tubers to survive and regrow in the spring. In cooler zones, dahlias are typically grown as annuals and replanted each year after the danger of frost has passed. In colder climes, proper winter care requires digging up and storing the tubers during the winter months, before replanting them in the spring. So, while dahlias may not be able to be grown as perennials in many regions of North America, they can still be grown as annuals and provide a beautiful addition to gardens and landscapes. If you are unsure of your USDA Hardiness Zone, you can determine it here.

How to Grow Dahlias: Choosing a Variety

There are over 50,000 different registered varieties of dahlias, and new varieties are being developed by breeders around the world. These varieties range in size from small, pompon-like blooms to large, dinner-plate-sized flowers, and come in a wide range of colors and shapes.
Dahlias are divided into several different categories based on their flower shape, size, and petal arrangement. Some of the most popular dahlia categories include:

• Single-flowered dahlias
• Mignon dahlias
• Anemone-flowered dahlias
• Waterlily-flowered dahlias
• Decorative dahlias
• Cactus dahlias
• Semi-cactus dahlias
• Ball dahlias
• Pompon dahlias
• Collarette dahlias
• Orchid-flowered dahlias

With so many possibilities from which to choose, the process can be rather daunting. Single-flowered dahlias have a simple yet elegant appearance, with a central disc surrounded by a single row of petals, making it a good choice for those who prefer a classic, traditional look. Pompon dahlias have a round, ball-shaped flower head made up of tightly-packed, fluffy petals, which can provide a more playful and whimsical display. Semi-cactus dahlias have elongated petals that are pointed at the tips, giving them a spiky appearance that can add texture and interest to a garden. Orchid-flowered dahlias have petals that are wider and more rounded, resembling the shape of an orchid flower. These dahlias are often prized for their striking beauty and intricate patterns. With so many varieties to choose from, gardeners can find a dahlia to suit almost any taste or garden style.

Honor Your Skill Set

Single-flowered dahlias are generally considered easier to grow than more complex dahlias like cactus or orchid-flowered varieties. Dahlias in the pompon group are also relatively easy to grow, although they may require some extra support to prevent their heavy blooms from flopping over. It’s important to choose dahlias that are well-suited to your particular growing conditions and level of experience and to provide them with proper care to ensure their success.

How to Grow Dahlias: Preparing the Bed

Location, Location, Location!

Once you have selected the variety of dahlia you wish to grow and have (optimally) purchased the tubers, it’s time to get your hands dirty! Choosing the right location for your dahlia flower bed is crucial. Dahlias require full sun and well-draining soil to thrive. Therefore, choose a location that receives at least six hours of direct sunlight per day and has good drainage. Once the location has been selected, work the soil in the entire flower bed before planting dahlias. Working the soil refers to the process of preparing the soil in a garden bed before planting. It involves digging, tilling, or turning over the soil to loosen it, creating a crumbly texture that roots can penetrate, aiding the plant’s growth. This process helps improve soil drainage, aeration, and water retention.

Turning the Soil

The extent to which the soil needs to be worked depends on the condition of the ground. In some cases, the soil may only need to be lightly raked or turned over with a garden fork, while in other cases, the soil may need to be tilled deeply to create a healthy growing environment for your dahlias. Working the soil also allows you to add any necessary amendments, such as compost or aged manure, to improve soil fertility and structure. However, if you are only planting a few dahlias, you can dig individual holes for each tuber, making sure to loosen the soil at the bottom of the hole. Mix in any amendments as needed.

Adding Amendments

Before getting down to the actual business of planting your dahlias, it’s a good idea to test your soil’s pH to ensure it falls between 6.0-7.0, which is ideal for dahlias. The easiest way to test your garden soil’s pH levels is to use a soil pH testing kit, which can be purchased at most garden centers or online. Soil pH testing kits typically come with test strips or a probe that measures the pH level of the soil. To use a test strip, simply insert it into the soil and wait a few seconds for the color to develop. Then match the color of the strip to the chart provided to determine the pH level. To use a probe, insert it into the soil and wait for the reading to appear on the display.

Another option is to send a soil sample to a soil testing laboratory for a more accurate analysis of your soil’s pH level, as well as its nutrient content. Soil testing laboratories can be found online or through your local agricultural extension office. A pH level lower than 6 indicates that the soil is too acidic for dahlias. Amending the soil with lime, which can be purchased at garden centers or online, will result in higher alkalinity. Follow package directions for the most favorable results.

How to Grow Dahlias: Planting the Tubers

Dahlias are grown from tubers, which are large underground stems that store and deliver energy and nutrients for the plant. To plant dahlias, dig a hole that is 6-8 inches (15-20 cm) deep and wide enough to accommodate the size of your dahlia tuber. If you are planting more than one dahlia, space the holes about 12-18 inches (30-45cm) apart, depending on the size of the variety.

When planting the dahlia tuber, place it in the hole with the eye facing up, which is the small indentation or bump on the tuber where new growth will emerge. The eye should be about 2 inches (5 cm) below the soil surface. Cover the tuber with soil and water thoroughly, being careful not to overwater. As the dahlia grows, continue to water regularly, making sure the soil stays moist but not waterlogged.

It’s important to give dahlias enough space to grow and spread out. Depending on the size of the variety you have selected, your dahlias can grow anywhere from 1-6 feet (30 cm -1.8 m )tall and 1-3 feet (30 cm – 1 m) wide. Planting them too close together will result in stunted growth and crowding. Be sure to follow the recommended spacing guidelines for the variety you are planting.

Best Time for Planting

it is important to wait until after the last frost date in your area before planting dahlia tubers to ensure they have the best chance of survival and growth. Last frost dates vary by region. The best way to determine the last frost date in your area is to consult a local gardening resource, like your local extension office. Another option is to use an online tool or app that can help you determine the last frost date in your area based on your zip code or location. These tools typically use data from local weather stations to provide accurate information on when the last frost is likely to occur in your area.

Five Fab Facts about Dahlias

• Dahlias are named after 18^th-century Swedish botanist Anders Dahl, who categorized them as vegetables because of their edible tubers!
• During the Victorian era, dahlias were a symbol of commitment and an everlasting union. Dahlias continue to be a popular choice for weddings.
• Some dahlia flower heads grow to 1 foot (30 cm) in diameter.
• Dahlias are indigenous to Mexico where they are called acoctli. Acoctli means water pipe. In ancient times, their long hollow stems were used for transporting water.
• There are no blue dahlias! However, breeders are actively trying to create a dahlia with beautiful blue blooms.