Rose & Flower Gardening
How to Grow Dahlias
With its many faces, you could call the dahlia the chameleon of the cutting garden.
Dahlia blooms can be as large as a dinner plate or as small as a golf ball. There are single dahlias (with one row of petals and a big center), double dahlias (with lots of petals in multiple rows), or even pom-pom shaped dahlias. You’ll find them in shades of pink, purple, red, yellow, orange, and white—some are even multi-colored. In other words, there are many different varieties! Dahlias are beautiful as cut flowers and last for several days in a vase, and you’ll often see them included in wedding bouquets.
It’s no surprise, then, that there are dahlia societies and clubs, dahlia shows, and dahlia collectors. Start growing dahlias and you might find yourself swept up in the urge to find and nurture hard-to-find varieties. No two look just alike and they’re all gorgeous, so who could blame you?
How to Choose Dahlias
The main thing to consider when choosing dahlias is the space you have available to grow them. Some dahlias can grow to heights of 5 or 6 feet, while others are much shorter and will live happily in a pot. Because there are hundreds of different cultivars and varieties, the only way to know the eventual size of a dahlia is to read the plant tag or the description in the catalog or online—something you should definitely do. After all, who wants to have to yank out a big, beautiful plant right before it blooms because it’s outgrowing its space?
Where to Plant Dahlias
Dahlias are sun lovers, so plant them where they’ll receive at least 6 hours of sunlight per day. In the South and other warm climates, a bit of afternoon shade during the hottest part of the day is fine, as long as they’ve received sun the rest of the day. When growing in pots, choose dahlia varieties that top out at 2 feet or less when fully grown.
When to Plant Dahlias
Look for dahlias when you shop for summer flowering bulbs. While “baby” dahlias are sometimes called bulbs, they’re really tuberous roots. Plant them outside when you plant your peppers, tomatoes, and other summer veggies. If you live where you can’t plant tomatoes and peppers outside until June, you can give your dahlias a head start by planting them in pots inside in April. Choose a pot that is about 3 to 4 times as wide as the tuber or clump of tubers. Once warm weather arrives, you can either move the pots outside or transplant the dahlias into the garden.
How to Prepare the Soil for Planting Dahlias
While easy to grow, dahlias do appreciate and thrive in soil that’s right for them, which means no heavy clay or soils with standing water. Improve the soil for strong root growth by mixing 3 inches of Miracle-Gro® Garden Soil for Flowers into the top 6 inches of existing soil, or focus on individual planting holes by blending equal amounts of garden soil and native soil. If you plan to grow your dahlias in containers, fill the pots with Miracle-Gro® Potting Mix to provide just the right environment for strong roots.
How to Plant Dahlias
First, determine the ideal spacing for the types of dahlias you plan to grow. Lay the tubers out on the soil, properly spaced, then bury them 4 to 6 inches deep, on their sides. (To get your dahlias off to an excellent start, drop a Miracle-Gro® Quick Start® Planting Tablet into each hole before adding the tuber.) Next, put down a thin layer (1 to 2 inches) of mulch to help keep the soil consistently moist.
How to Stake Dahlias
Since dahlia flowers can be heavy and you don’t want the stems to break just as the blooms are about to open, you’ll want to give each plant some support. For best results, do this either at planting time or before the plants are over 6 inches tall. Simply use a wooden or bamboo stake or a tomato cage for individual plants. Growing a bunch of dahlias in a row? Use stakes and twine to create a lattice system along the row by weaving the twine between the stakes, leaving holes for the dahlias to grow through.
How to Water Dahlias
Once you see new growth, start watering regularly, keeping the soil about as damp as a well wrung-out sponge. Until you start to see that new growth, though, only mist the ground lightly (or not at all)—adding any more moisture at that point may encourage the tubers to rot. Know, too, that the bigger the plant, the more water it will use, so you will likely have to water more as the summer progresses.
How to Feed Dahlias
To maximize blooms, you'll want to complement the great soil we mentioned above with just the right plant food. Begin feeding dahlias with Miracle-Gro® Water Soluble Bloom Booster® Flower Food 30 days after planting (be sure to follow label directions). Designed specifically for flowers, it goes easy on the nitrogen (which encourages lots of leaves) and contains more of the phosphorus needed for beautiful flowers. Feed dahlias every 7 to 14 days until the plant naturally stops blooming at the end of the season. Bonus: When you plant in Miracle-Gro® soil and feed with Miracle-Gro® plant food, you’ll see up to 3 times the blooms vs. unfed plants over the growing season—when used as directed, of course!
How to Prevent Problems with Dahlias
Snails and slugs are the biggest pest problems for dahlias, and they can be controlled by sprinkling diatomaceous earth or a snail and slug control product like Miracle-Gro® Nature’s Care® Slug & Snail Control at the planting site (be sure to follow label directions). Sometimes spider mites can be an issue as well, and neem oil will take care of those. In addition, during hot, humid summers, powdery mildew can coat the plant leaves. There’s not a lot you can do about this beyond making sure to keep leaves as dry as possible when you water the plants and making sure to space them properly when you plant, to allow for ample air flow.
How to Deadhead and Disbud Dahlias
Want more dahlia flowers for a longer period of time? Snip off flowers as soon as they begin to fade. You can also try “disbudding,” which is when you remove some of the extra flower buds from the stems so the plant puts its energy into fewer flowers that will then grow larger. Just pinch off the two buds near the base of the main flower stem when they show up and let the main flower open.
How to Harvest Dahlias
Cut dahlias in the morning, before the heat of day sets in. Use a sharp pair of shears or harvest snips and make sure to choose blooms that are fully open, with no green center visible. (Unlike peonies, dahlia buds won’t open after they’re cut.) To enjoy their beauty longer*, place stems in a vase containing water and Miracle-Gro® for Fresh Cut Flowers—add according to the label directions. Be sure to change the water and add more Miracle-Gro® every 2 to 3 days.
* vs. water only, following label directions
How to Overwinter Dahlias
You can leave dahlias in the garden if you live in zone 8 or higher. In colder areas, though, you’ll need to bring them inside. Here’s how: Wait for a frost, then dig up the dahlia tubers and cut off the stems. Let the tubers sit in a dark, cool place for a few days to dry out, then pack them in between sheets of newspaper. Store them during the winter in a cool, dry spot, such as a closet or insulated garage.
How to Divide Dahlias
If you’ve successfully kept dahlias through the winter, you can divide them in the spring. Simply break apart the clump of tubers, taking care to leave one eye (or stem end) on each piece. Then replant!
How to Grow Dahlias: Recap
- Choose dahlias that will grow well in the space you have available for them.
- Prepare the soil by adding Miracle-Gro® Garden Soil for Flowers for in-ground gardens or Miracle-Gro® Potting Mix for containers.
- Plant dahlias in full sun (with some afternoon shade where it’s hot) in the spring.
- Place stakes next to the tubers at the time of planting or when the plants are small.
- Water plants once they begin to grow, keeping the soil about as moist as a wrung-out sponge.
- A month after planting, feed plants every 7 to 14 days up through budding and flowering with Miracle-Gro® Water Soluble Bloom Booster® Flower Food.
- Deadhead and disbud to encourage big blooms.
- Pick open dahlia blooms in the morning and keep stems in water mixed with Miracle-Gro® for Fresh Cut Flowers.
- Divide dahlias in the spring before planting.