When Should You Dig Up and Store Dahlia Tubers?

Dig dahlia tubers in Western Pennsylvania in the second half of October or early November, once frost has ended the bloom and before the ground freezes. NOAA's 1991 to 2020 climate normals for Pittsburgh International Airport put the median date of the first 32-degree night at October 23, so that week is the usual signal to get the garden fork out.

The frost date is a range, and waiting for it is optional. The same NOAA data shows a 1 in 10 chance of a freeze by October 9 and a 9 in 10 chance by November 6. Penn State Extension states that it is unnecessary to wait for the first frost at all, as long as the plants have been in the ground for at least 120 days, which is how long dahlias need to produce mature tubers for storage. This post covers the local frost window, how to dig and divide, how long to dry the tubers, and where to keep them until spring.

What is a dahlia tuber, and why can't it stay in the ground here? 

A dahlia tuber is the fleshy underground root that stores the plant's energy over winter and sends up new growth the following year. Each plant makes a clump of them in a single season.

Western Pennsylvania winters are hard on that clump. Penn State Extension notes that heavy freezing and winter rains can promote rotting, especially in USDA Hardiness Zones 6 and lower. Oakmont, Verona and Fox Chapel fall in zone 6b on the 2023 USDA map, and the center of Pittsburgh sits in the slightly warmer zone 7a.

The Penn State author does report that tubers left by accident in protected spots close to a house have survived. That is a gamble with plants that took a full season to grow, and lifting them is the dependable choice. 

When does the first frost arrive in the Pittsburgh area?

NOAA's 1991 to 2020 normals for Pittsburgh International Airport give three dates for the first 32 degree reading of fall:

• October 9: a 10 percent chance that a freeze has already occurred
• October 23: a 50 percent chance, the median year
• November 6: a 90 percent chance

The median first night at 28 degrees, a harder freeze, is November 4.

Those figures come from the airport, west of the city. Conditions in a river town or a city neighborhood can differ on any given night, so treat the dates as a planning window and watch the local forecast as October goes on.

Do you have to wait for frost before digging? 

No. Penn State Extension is direct on this point: waiting for the first frost is unnecessary. What the plant needs is time. Dahlias must be in the ground for at least 120 days to produce mature tubers for storage.

Counting forward from planting day gives the earliest safe date. A dahlia planted on May 15 reaches 120 days on September 12. Anything after that is a choice between more flowers and an easier digging day.

Waiting has its appeal, for the reason the Penn State author gives: to enjoy every single bloom. The trade-off is the weather on digging day, since a mild, dry afternoon in mid-October is easier work than cold mud after a freeze.

How do you dig and divide dahlia tubers?

Penn State Extension describes the process in a few steps:

• Cut the stalk down to a height that makes the clump easy to carry.
• Lift the clump with a pitchfork.
• Shake off the soil, or use a hose if the soil clings.
• Decide whether to divide now or in spring.

Dividing in fall or spring both work. Penn State notes that tubers are more manageable to cut in the fall, while the eyes, the points where new shoots form, are more visible in spring. Fall division saves storage space. Storing whole clumps takes more room, and Penn State recommends not washing the soil off clumps that will be stored undivided. 

A division only grows if it has the right parts. According to Penn State, each tuber must have a neck and a crown to carry a viable eye, and viable tubers are always attached to the old stalk. Necks thinner than a pencil will probably dry out by spring. A tuber that looks healthy but has no eye is called a blind tuber, and it will not produce a plant.

Label as you go. The dahlia society guide suggests writing the variety name on each tuber with a permanent marker, since paper labels and bags can fall apart in storage. 

How long should tubers dry before storage?

The usual recommendation is 24 to 48 hours. The Penn State Extension author found that was not enough and now lets rinsed tubers dry for four or five days out of the sun, because tubers stored too damp were more prone to rot.

Trim the roots before drying. Penn State notes that leaving them on can hold too much moisture.

Where should dahlia tubers be stored over winter?

Store tubers somewhere that stays between 40 and 50 degrees and never freezes. That is the range the Penn State Extension author keeps and the range the Greater Philadelphia Dahlia Society calls ideal in a storage guide shared by the American Dahlia Society. Penn State also says to keep containers off cement floors. 

The Dahlia Society guide describes what goes wrong outside that range:

• Too cold: tubers freeze and die.
• Too warm: tubers sprout and rot. The author lost tubers in a basement that ran in the mid-70s.
• Too dry: tubers shrivel.

For containers, the Penn State author uses plastic bins with lids, drills holes in the sides for airflow, layers the tubers in cedar shavings, and leaves the lid unlatched. Coarse vermiculite and wood chips are other media named in the dahlia society guide. Penn State advises against cardboard boxes, newspaper and paper bags because they wick up too much moisture.

Check the bins after a few weeks. If the shavings feel moist, replace them. Penn State notes that too much moisture is the usual problem in the first month, and that a light spritz of water can help later in winter if the medium becomes too dry. An inexpensive thermometer in the storage spot takes the guessing out of it.

When can dahlias go back in the ground?

Replanting waits for spring. NOAA's normals for Pittsburgh International Airport put the median last 32-degree night at April 23, with a 1 in 10 chance of a freeze after May 12. Penn State Extension's companion article, The Dirt on Dahlias, covers the growing season. 

Tubers that were divided in fall are ready to plant as they are. Clumps stored whole can be divided in spring, when the eyes are easier to see. 

FAQ

Can dahlias stay in the ground over winter in Pittsburgh? 

It is a risk. Penn State Extension says heavy freezing and winter rains can promote rotting in zone 6 and colder, and Oakmont, Verona, Fox Chapel and New Kensington are all zone 6b.

Should you wash dahlia tubers before storing them?

Wash them if you are dividing in fall, then dry them for several days. Penn State recommends leaving the soil on clumps that will be stored whole.

What is a blind tuber? 

A blind tuber looks healthy but has no eye, so it cannot grow a new plant.

Can you store dahlia tubers in a cardboard box?

Penn State Extension advises against cardboard boxes, newspaper and paper bags because they wick up too much moisture. A vented plastic bin with cedar shavings or coarse vermiculite is a better choice.

What temperature is too warm for stored tubers?

The Greater Philadelphia Dahlia Society guide reports sprouting and rot in a basement in the mid 70s and describes 40 to 50 degrees as ideal, with the 50s working reasonably well. A room kept at normal household temperatures is warmer than that.

How many days do dahlias need before tubers are mature?

At least 120 days in the ground, according to Penn State Extension. 

Dahlias at Roots to Petals in Oakmont

Dahlias are where it all started for Roots to Petals. The Oakmont florist and plant studio reports growing more than 100 varieties in 2026 across three garden locations, and its seasonal dahlia subscription offers weekly bouquets from those gardens beginning around late July, weather permitting. Dahlia growing is also one of the topics in the shop's workshops, many of them held around the workshop table at the studio on Allegheny Avenue.

For more local growing and flower reading, see the shop's posts on flowers to plant in the fall in Oakmont, why locally grown flowers make a difference, and where to find flowers, plants and workshops in Pittsburgh. 

Visit Roots to Petals or call 412-822-6023 today. Contact us for more information.