5 Easy Steps for Growing Dazzling Dahlias in Pots That Bloom All Summer Long

Dahlias are one of those flowers people become obsessed with. They’re available in nearly every color, blooms come in many shapes and sizes, and new varieties come from breeders every year. And even if you don't have garden space for dahlias, these plants grow well in containers. Here's how to grow dahlias in pots so you can enjoy their beautiful blooms wherever you have a sunny spot.

Best Dahlias for Containers

Take a look at the selection of dahlias, and you might quickly be overwhelmed. While all can be grown in a container, some are better suited than others. Consider plant size, whether you’ll be purchasing started plants or tubers, and bloom time (and color, of course) when picking dahlias for a container garden.

Bloom Time

Dahlias can be categorized as early, mid, or late bloomers. Early bloomers begin to flower around 75 days after planting, mid-season around 90 days, and late bloomers can take 120 days to start flowering. Many of the largest dahlias, sometimes called dinner plate dahlias, are in the late-blooming category. Dahlias continue blooming until frost, but if you don’t have four months until your frost, planting late-blooming dahlias could be disappointing.

Plant Size

Dahlias can be 12-inch-tall dwarf plants or 6-foot-tall virtual bushes loaded with blooms. The largest dahlias are less suited for most container sizes. However, tons of dahlia varieties and flower colors, shapes, and sizes are available in the 3- to 4-foot size range, which is manageable for a large container. Consider your space as well. Do you have room for a 5-foot-tall, 3-foot-wide plant on your balcony? 

Plant or Tuber?

Dahlias are available as pre-started plants from garden centers and plant sales, but they can also be purchased as tubers, which are much more economical. You’ll also find more variety when shopping for tubers. Tubers are as easy to plant as potatoes, but many people prefer to buy a dahlia plant or two and plunk them into a pot for instant gratification. 

How to Plant Dahlias in Pots

Planting dahlias in pots is similar to planting them in the ground. Good drainage, a spot in full sun, fertile soil, and adequate space are all factors in successfully growing dahlias in pots.

1. Choose a Large Pot

Dahlias can grow large and need lots of nutrients to fuel all that growth. They won’t achieve their full potential in a small pot. Choose a container that's at least 12 inches in diameter and 10-12 inches deep for dwarf dahlias. Larger varieties need a bigger pot. Wooden half-barrels or other spacious pots work well. Of course, make sure there are drainage holes in any container you choose.

2. Add Soil and Amendments

Any high-quality potting mix works for dahlias. If your potting mix doesn't include fertilizer, add compost, aged manure, or other organic source of nutrients. A little perlite and vermiculite will keep the soil loose and retain moisture for those sunny days when you haven’t gotten around to watering yet.

3. Provide Staking

Most dahlias, especially in containers, benefit from staking. Use a stout wooden stake and place it in the soil near the center of the pot after filling it with soil. When you plant the dahlia tuber, dig down, put the eye end near the stake, and replace the soil. The dahlia stem will grow right next to the stake for easy trussing. Tomato cages can also be used, but they aren’t as pretty.

4. Plant the Tuber or Transplant the Sprouted Dahlia

After installing the stake, make a hole 4-6 inches deep for the tuber. It will have a piece of the old stem or root collar and a longer body. The end with the eye (where the old stem was) should be planted where you want the plant to come up in the pot, generally in the center. Plant the entire tuber horizontally, not vertically. The direction the body of the tuber points doesn’t matter.

Cover the tuber with 3-4 inches of soil. When planting more than one variety, add a label to the stake so you’ll remember which one it was. Tubers don’t need to be watered (if the potting mix was moist) until they’ve sprouted and are 3-4 inches tall. 

Dahlia plants from a garden center can be transplanted into a larger pot like any other plant. Make the hole, remove the plant from its nursery pot, loosen the roots if needed, and plant it about the same depth as it was. Firm the soil and water it in. Add a stake or cage right away.

5. Water and Fertilize the Dahlias

Dahlias in pots can be thirsty. The soil in a container dries more rapidly than in a traditional garden bed, and for large dahlias, you’ll often need to water daily. Check the soil with your finger, sticking it down as deep as you can. If it’s dry more than about a knuckle down, it’s time to water. 

Fertilize dahlias with slow-release granules at planting time, or use a diluted liquid product when watering. While many “bloom-booster” products are touted as the best thing for flowering plants, dahlias aren’t picky. Any general-purpose flower and vegetable fertilizer will do, providing lush growth and bright blooms. Follow the directions on the package for how much to feed and how often.

What to Grow with Dahlias in Pots

A large container can support one dahlia or two or three, depending on their size. However, that doesn’t mean you can’t use a dahlia as the thriller in a traditional thriller, filler, and spiller container design. Dahlias grown from tubers won’t bloom until at least midsummer, so choose something that blooms earlier for the filler to provide color before the dahlias bloom. Try some French marigolds, short snapdragon varieties, or begonias.

Add a spiller, such as petunias or sweet potato vines, to cascade down the front of the pot. Don’t forget the stake near the center to help support taller dahlias.