The Complete Dahlia Guide: Planting, Pinching, Cutting and Storing Tubers

Dahlias are tender perennials. In Zone 7 they survive some winters in the ground and rot in others, so most of us dig the tubers after the first frost and store them cool and dry until spring. Plant them after your last frost, cut the growing tip out when the plant is about a foot tall, and cut the flowers hard all season. Those three things make the difference between a few blooms and an armload every week.

Do dahlias come back every year?

It depends on where you are. Dahlias are hardy in zones 8 and warmer. We sit in Zone 7, which is the gamble zone. A mild winter with dry ground and they come back fine. A wet winter and the tubers rot where they sit.

You have two options. Mulch heavily and take your chances, or dig them. We dig, because a clump you lift in November is also a clump you can divide in spring, and one tuber becomes five or six over a season. That multiplication is half the fun.

Planting dahlias

• Wait for warm soil. After your last frost, when the ground is around 60 degrees. Tubers put in cold wet soil rot before they sprout.
• Four to six inches deep, laid on their side with the eye pointing up.
• Do not water them in. This is the one that catches people. A tuber has everything it needs to sprout. Watering before there is a shoot is the most common way to lose one. Wait until you see green.
• Full sun, six to eight hours, in soil that drains.
• Put the stake in now, at planting, while you can see exactly where the tuber sits. Driving a stake into an established clump in August means spearing it.

The cut that doubles your blooms

This is the hardest thing to make yourself do and the single best thing you can do for a dahlia.

When the plant is about 12 inches tall, take sharp clean snips and cut the main stem at a 45 degree angle right above the third set of leaves. You are removing the growing tip on purpose.

It feels like vandalism. It costs you a couple of weeks. What you get is a plant that branches from every node below the cut instead of running one stem straight up, which means many more stems and many more flowers. The same principle runs the whole cutting garden, which is why we keep a pinch list. Zinnias respond exactly the same way.

Cutting dahlias for the vase

Two things worth knowing, because dahlias do not behave like other cut flowers.

• They do not open after cutting. A dahlia picked in bud stays a bud. Cut when the flower is almost fully open and the back petals are still firm, not soft or papery.
• Cut deep. Go well down the stem, back to a set of leaves, even if it feels like you are taking too much. Short snips off the top give you short stems and a lazy plant.

Cut in the early morning, straight into a bucket of water. Expect about five days in the vase, longer if you change the water.

Digging and storing dahlia tubers

There is something satisfying about lifting a clump and seeing how much happened underground while you were not looking. One tuber goes in, a fistful comes out.

1. Wait for frost to blacken the foliage. That is the signal. Cut the stems back, leaving four to six inches above ground so you have a handle.
2. Loosen carefully with a fork or spade, working well outside the clump. Tubers sit wider than you think and a spade through one is a tuber lost. Lift the whole clump.
3. Rinse them off. Shake the loose soil away, then wash them thoroughly so you can actually see damage or rot.
4. Dry completely. Lay them in a single layer on paper towels or another breathable surface. This step is not optional. A tuber stored damp molds.
5. Label one tuber per clump with a Sharpie, variety or color. Next spring you will not remember, and everybody thinks they will.
6. Pack in something breathable. Pine shavings, peat moss or sawdust, in a cardboard box or a bin with ventilation holes. Never airtight. Trapped moisture is rot.
7. Store at 40 to 50 degrees, cool and dark.

Check on them a few times over winter. Shriveled means too dry, so mist the shavings lightly. Anything soft or moldy comes out immediately before it spreads to its neighbors.

We do not divide until spring. You can divide in fall if you prefer, but the eyes are much easier to see once the tubers have started to wake up, and every division needs at least one eye to grow.

Dahlia questions we get asked

Do dahlias come back every year?

In zones 8 and warmer, yes. In Zone 7 and colder they are a gamble, because the tubers rot in wet winter ground. Most gardeners here lift them after the first frost and store them dry until spring.

When should you plant dahlia tubers?

After your last frost, once the soil is around 60 degrees. Planting into cold wet ground is the most common way to lose a tuber before it ever sprouts.

Should you water dahlias after planting?

No. Wait until a green shoot appears. A tuber holds everything it needs to sprout, and water before there are roots to use it causes rot.

How do you pinch a dahlia?

When the plant is about 12 inches tall, cut the main stem at an angle just above the third set of leaves. Removing the growing tip forces the plant to branch, which gives you far more stems and flowers.

Why are my dahlias not blooming?

Usually too much shade, too much nitrogen, or a plant that was never pinched. Dahlias want six to eight hours of sun, and feeding heavy on nitrogen gives you a beautiful leafy plant and almost no flowers.

When do you dig up dahlia tubers?

After the first frost blackens the foliage. That frost is the signal the plant has gone dormant and the tubers are ready to lift.

How do you store dahlia tubers over winter?

Wash them, dry them completely, label them, and pack them in pine shavings, peat or sawdust in a ventilated box at 40 to 50 degrees. Never seal them in an airtight container.

Why did my stored tubers shrivel or rot?

Shriveled means the storage medium was too dry, so mist it lightly. Rot means they went into storage damp or were stored airtight. Check them a few times over winter and pull anything soft.

When should you divide dahlia tubers?

Spring, once the eyes have started to swell and you can see them. Each division needs at least one eye or it will never sprout.

Do dahlias open after you cut them?

No. Unlike many cut flowers, a dahlia picked in bud stays a bud. Cut when the flower is nearly fully open and the back petals are still firm.

Why we keep growing them

One tuber becomes a clump. A clump becomes five plants. Five plants become an armload of flowers a week from midsummer until frost takes them. Few things in the garden pay back like that, and the lifting and storing is a small price for it.

Growing more flowers? Our Growing Flowers guide brings all of our flower guides together in one place, from dahlias and zinnias to cool weather blooms and arranging.