Dahlias look like something only expert gardeners can grow, but they’re actually one of the most rewarding flowers you can plant. With a little sunshine, water, and support, they’ll produce armloads of blooms all summer long.

timing & location

Planting

Timing

Dahlias are warm-season flowers grown from tubers.

Plant them after the danger of frost has passed and the soil has warmed (usually when soil temperatures are around 60°F).

In colder climates, this typically means mid to late spring.

Location

Dahlias thrive in full sun. Aim for:

  • 6–8 hours of direct sunlight daily
  • Well-draining soil
  • A spot protected from strong wind if possible

The more sun they receive, the more flowers you’ll get.

spacing

Planting the Tubers

Plant dahlia tubers 4–6 inches deep with the “eye” (growth point) facing upward.

  • Planting tubers horizontally is generally recommended so you don't have to dig as deep of a hole, but you can plant vertically as well.

Spacing depends on the variety, but a good general rule is:

  • 12 inches apart for smaller varieties
  • 18 inches apart for large varieties

Cover with soil but do not water heavily until sprouts appear to prevent rot.

early support

Support the Plants

Most dahlias need support as they grow so they grow straight up and don't fall over (especially during a windy storm)

Place a stake or cage at planting time so you don’t accidentally stab the tubers later. Tie plants loosely to the stake as they grow taller.

If you grow lots of dahlias, you could stake the 4 corners of a ~10ft x 3-4ft area and use garden twine to make an x between the stakes to prop up a group of dahlias.

when to water

Watering

Water sparingly before sprouts emerge:

  • Water initially after planting
  • Periodic light watering when soil is dry.
  • Too much water before sprouts and tubers could rot.

After sprouts emerge:

  • Water deeply 2–3 times per week
  • Make sure soil drains well
  • Dahlias like consistent moisture but do not tolerate soggy soil.

Maintenance

Ongoing Care

Pinching for More Blooms

When plants reach 9-15 inches tall, pinch off the top growing tip.

This encourages the plant to branch and produce more flowers, resulting in a fuller plant.

Fertilizing

Dahlias benefit from fertilizing every 2–4 weeks.

  • Early on, before blooms, a fertilizer with equal parts nitrogen, phosphorus and potassium help the plant to grow strong
  • After blooms have begun, switching to a low-nitrogen fertilizer will encourage more blooms (less leaves)

enjoying your blooms

Harvesting Flowers

The more you cut dahlias, the more they bloom.

Cut flowers when they are three-fourths to fully open, since dahlias do not continue opening much after being harvested.

Dahlias typically last ~5 days in the vase. Replace water daily and keep out of direct sunlight to help your cut dahlias last longer.

Harvest regularly to keep plants producing.

After Frost

End of Season Care

In cold climates, dahlia tubers need to be dug up before winter.

After the first frost:

  • Tie a named label to the base of each plant
  • Cut stems back to about 6 inches
  • Carefully dig up the tubers with a pitchfork
  • They can then be replanted the following spring.

You may noticed I skipped a couple steps there. That is becuase there is a lot of mixed ideas on the absolute best way to store dahlias overwinter. The truth is, there are MANY ways to store tubers over winter and what works for me may not work for you.

I will, however, detail a couple of my thoughts in another post.

More on Tuber Storing

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