How to Grow Border Dahlias

Dahlias for Containers and Small Spaces

Few plants can compete with the flowering power of dahlias. These easy-to-grow, heat-loving summer bulbs bloom non-stop from midsummer through fall, making it easy to keep your yard and garden colorful all season long.

Most dahlias grow into bushy plants that stand 3 to 4 feet tall. Border dahlias are much more compact. At just 15 to 20” high, they are an ideal height for growing at the front of a flower bed, along a walkway, and in pots and planters. Don’t let their height fool you. These low-growing dahlias bloom with the same incredible energy as their full size cousins.

After evaluating many different types of border dahlias, we have found that the Melody and Gallery series are the best performers. Though each variety is slightly different in habit and flower size, Gallery dahlias tend to be the most compact (15" - 20" tall) and produce the greatest number of flowers per plant. Melody dahlias are several inches taller (24-30") and have a slightly more open habit.

When choosing border dahlias for your garden, here are some suggestions:

• To get the most uniform band of color, plant a single variety.
• To get a mix of colors with a relatively uniform height, choose varieties from within a single family (all Gallery or all Melody).
• For a taller and slightly more informal look, blend the two families, using the same or complementary colors (such as Gallery Singer and Melody Mambo).
• In garden beds, Gallery dahlias can be planted near the front edge and Melody dahlias in the mid-zone.
• Both types grow well in containers. Choose Gallery dahlias for a tight, mounding habit; Melody dahlias are taller and looser.

Growing Border Dahlias In Pots and Planters

A single border dahlia will fill a 10 to 12” pot. Pots of this size are easy to move around, so you can add a splash of color wherever it's needed. For a 24 to 30" diameter pot, three border dahlias will give you a nice, full look. Another option is to mix border dahlias with other sun-loving container plants. Here are some good companions:

• Coleus
• Verbena
• Canna Lily
• Creeping Jenny
• Lantana
• Liatris
• Sweet Potato Vine
• Million Bells
• Elephant Ears 

Where and When to Plant Border Dahlias

Dahlias are high-energy plants that need at least 6 hours of direct sunlight each day. The more sun they get, the more flowers they produce. In southern areas, they appreciate being protected from hot afternoon sun.

Dahlias will not tolerate freezing temperatures and they dislike cold soil. Do not put the tubers in the ground until all danger of frost has passed. In cold areas with short growing seasons (zones 3-5) dahlias can be planted in pots and given a head start in a greenhouse or under grow lights. Use your growing zone to determine the proper date for starting the tubers indoors. Simply count back 4 to 6 weeks from the last frost date.

Zone 3
Start Indoors: Late April
Plant Outdoors: Early to mid-June

Zone 4
Start Indoors: Mid-April
Plant Outdoors: End of May

Zone 5
Start Indoors: Early April
Plant Outdoors: Mid to Late May

Tips for Growing Border Dahlias in Containers

Dahlias have vigorous root systems that need plenty of room to develop. Each border dahlia tuber will need a 10 to 12” diameter container or 2-gallon pot. Larger containers can accommodate more than one dahlia tuber or some other types of plants. Pots should always have a drainage hole on the bottom to prevent the soil from getting waterlogged.

Here's how to pot up a border dahlia. Fill the container a little more than half way with good quality potting mix. Find the place where the tubers are joined, at the base of the old stem. Set the tubers on the soil with the stem area on top. It should be at least 4” below the top of the pot. Cover the tubers with about 2” of soil and water well. Put the pot in a warm, sunny place where it will get 6 or more hours of sun each day. As the tubers start to grow, you can gradually add more soil until the pot is almost full.

Once the plants are well established and 5 to 6" tall, start fertilizing them twice a month. When the first flower buds appear, cut back the tallest 2 or 3 stems to about half their height. This will help the plant fill out and increase total flower production. During the growing season, removing faded flowers will stimulate growth and keep the plants looking their best.

Dahlias should not be overwatered. It's best to let the top couple inches of soil get fairly dry between waterings.

TIP: Dahlias dislike cold weather. Though a chilly, early summer night won't kill them, it can set them back by several weeks. Pamper your young dahlia plants by keeping the pots in a warm, protected place until nighttime temperatures are consistently in the 60s.