Do I Need to Dig Up My Dahlia Bulbs?

Table of Contents

1. Introduction
2. The Short Answer: It Depends on Your Zone
3. Why Soil Drainage Matters More Than Temperature
4. Benefits of Leaving Dahlias in the Ground
5. How to Protect Dahlias Left in the Ground
6. Why Digging Up Tubers Is Often the Best Choice
7. When Is the Right Time to Dig?
8. How to Dig Up Dahlia Tubers Safely
9. Cleaning and Preparing for Storage
10. Identifying the Eyes and Dividing
11. Choosing the Right Storage Container
12. The Ideal Storage Environment
13. Spring Arrival: Bringing Them Back to Life
14. Common Myths About Digging Dahlias
15. Realistic Expectations for Overwintering
16. Summary of the Decision Process
17. FAQ

Introduction

Dahlias are the stars of the late-summer garden, offering a spectacular range of colors and shapes that last until the first frost. The excitement of seeing a dinnerplate-sized bloom for the first time is a feeling every gardener remembers. At Longfield Gardens, we believe these stunning dahlias are some of the most rewarding plants you can grow.

As the growing season winds down, many gardeners wonder if they need to lift their tubers or if they can stay in the ground. This guide is for anyone who wants to ensure their dahlias return year after year with more vigor and beauty. We will explore how your local weather and soil conditions determine the best course of action. Whether you choose to dig them up or tuck them in for the winter, the process is straightforward and successful with a few simple steps. The excitement of seeing dinnerplate dahlias for the first time is a feeling every gardener remembers.

The Short Answer: It Depends on Your Zone

The most direct answer to whether you need to dig up your dahlia tubers is based on your USDA plant hardiness zone map. These zones are a standard way to determine which plants are likely to survive the winter in your specific location.

Dahlias are tropical plants native to Mexico and Central America. Because they evolved in a warm climate, they do not naturally tolerate freezing temperatures. In the United States, we generally use USDA Zone 8 as the dividing line.

If you live in Zone 8, 9, 10, or 11, your winters are usually mild enough that dahlia tubers can stay in the ground. The soil in these regions rarely freezes deep enough to reach the tubers. In these warmer areas, a simple layer of mulch is often all the protection they need to stay cozy until spring.

If you live in Zone 7 or colder (Zones 3 through 6), the ground will freeze deep enough to damage or kill the tubers. For gardeners in these regions, digging and storing the bulbs indoors is the most reliable way to keep your favorite varieties alive. While some gardeners in Zone 7 might find success leaving them in the ground during a mild winter, digging them up is the only way to ensure they survive a cold snap.

Key Takeaway

• Zones 8 and warmer: You can usually leave dahlias in the ground with extra mulch.
• Zones 7 and colder: Digging and storing tubers is recommended for winter survival.
• Check your soil: Regardless of your zone, tubers in wet, heavy soil are more likely to rot.

Why Soil Drainage Matters More Than Temperature

Even in a warm climate, temperature is only half of the story. The other critical factor is drainage. For a closer look at site selection, see Where Do Dahlias Grow Well?

Dahlia tubers are essentially storage tanks for water and nutrients. If they sit in cold, soggy soil for weeks at a time, they are very likely to rot. This is true even if the air temperature never drops below freezing. If your garden has heavy clay soil—which holds onto water like a sponge—leaving your tubers in the ground is risky.

On the other hand, if you have sandy soil or well-amended garden beds where water moves through quickly, your tubers have a much better chance of surviving. When deciding whether to dig, look at your garden after a heavy autumn rain. If puddles remain for more than an hour or two, your soil is likely too wet for safe overwintering.

Benefits of Leaving Dahlias in the Ground

If you live in a mild climate and have well-draining soil, leaving your dahlias in the ground has several advantages. It is a great time-saving option for busy gardeners.

First, dahlias that stay in the ground often start blooming earlier in the summer. Because they don't have to be replanted and wait for the soil to warm up in a storage container, they can begin growing as soon as the spring sun warms the earth. This can give you an extra two or three weeks of flowers.

Second, undisturbed dahlias can grow into very large, impressive clumps. These established plants often produce a higher volume of blooms because they have a massive root system already in place. Varieties like Kelvin Floodlight can become spectacular focal points when they have been in the same spot for a few years.

Finally, leaving them in the ground is simply less work. If you have a large collection of dahlias, skipping the digging, cleaning, and storing process can save you hours of effort in the fall.

How to Protect Dahlias Left in the Ground

If you decide to leave your dahlias outdoors, you can't just walk away and hope for the best. They still need a little bit of care to survive the winter months. Think of this as "tucking them in" for a long nap.

Wait for the first frost to turn the foliage brown or black. Once this happens, the plant has stopped growing and is entering its dormant phase. Cut the stems down so they are only about 2 or 3 inches above the soil level.

The most important step is adding a thick layer of mulch. Mulch acts like a blanket, keeping the soil temperature steady and protecting the tubers from light frosts. You can use several different materials for this:

• Wood chips or bark: These provide great insulation and stay in place well.
• Clean straw: A 6-inch layer of straw is an excellent insulator.
• Pine needles: These are lightweight and allow some air to circulate while keeping the ground warm.
• Dry leaves: If you shred them first, they make a wonderful, free mulch.

In areas where winters are particularly wet, some gardeners place a piece of heavy plastic or a waterproof tarp over the dahlia bed after mulching. This helps keep the soil dry, which is the best defense against rot. Just be sure to remove the plastic as soon as the weather warms up in early spring so the plants can breathe and grow.

Why Digging Up Tubers Is Often the Best Choice

While leaving them in the ground is easier, there are many reasons why even gardeners in warm zones choose to dig up their dahlias. Digging is not just about survival; it is about garden management.

The most common reason is to divide the plants. A single dahlia tuber planted in the spring can turn into a clump of 5 to 15 tubers by the end of the summer. If you leave that clump in the ground year after year, it will eventually become overcrowded. Overcrowded plants compete with themselves for nutrients and water, which leads to smaller flowers and weaker stems. By digging them up every year or two, you can divide the clumps and turn one plant into five.

Another benefit of digging is the ability to rethink your garden design. If you dig up your tubers, you aren't committed to the same layout next year. You can move your Cafe au Lait dahlias to a more prominent spot.

Or group colors together for a more striking display with the Harvest Collection.

Lastly, digging gives you total control. When your tubers are stored in a controlled environment, you don't have to worry about an unusually cold winter or a record-breaking rainy season. You know exactly what condition they are in, and you can monitor them throughout the winter.

When Is the Right Time to Dig?

Timing is one of the most important parts of the digging process. If you dig too early, the tubers may not be fully mature. If you wait too long, they could be damaged by a deep freeze.

The best time to dig is about two weeks after the first "killing frost." This is the frost that turns the green leaves and stems of your dahlias black or dark brown. While the top of the plant looks dead, this period is actually very important for the tubers. The cold snap signals the plant to go dormant and send all its remaining energy down into the roots. This makes the tubers "cure" and develop a tougher skin, which helps them survive storage.

If you live in an area that doesn't get a hard frost until very late in the year, you can simply wait until mid-November. By this time, the days are short and the soil is cool enough that the plants will naturally start to slow down.

What to do next:

1. Keep an eye on your local weather forecast for the first frost.
2. Once the foliage turns black, cut the stems down to 4 inches.
3. Wait 10 to 14 days before lifting the tubers from the soil.
4. Tag each variety clearly before you move them so you don't forget which is which.

How to Dig Up Dahlia Tubers Safely

Digging up dahlias is a satisfying task, but it requires a gentle hand. The "neck" of a dahlia tuber—the part where the tuber connects to the main stem—is very fragile. If the neck breaks, the tuber will usually not grow, because the "eyes" (the sprouts) are located on the crown right where the neck meets the stem.

Start by using a garden fork rather than a shovel. A fork is less likely to slice through the tubers. Position your fork about 12 inches away from the main stem. This ensures you are outside the main clump of tubers.

Push the fork deep into the soil and gently pry upward. Move to the other side of the plant and do the same thing. You want to loosen the soil all the way around the plant until you can lift the entire clump out of the ground by its base. Never pull on the stems to get the plant out of the ground, as this is the easiest way to break the necks.

Once the clump is out, gently shake off the loose soil. You can use your fingers to poke away larger chunks of dirt, but be careful not to scratch the skin of the tubers.

Cleaning and Preparing for Storage

Once your dahlias are out of the ground, they need to be cleaned. Some gardeners prefer to wash their tubers with a garden hose to remove all the soil. This makes it easier to see the "eyes" if you plan to divide them right away.

If you do wash them, make sure they dry thoroughly. Rot is the biggest enemy of stored dahlias, and moisture is the primary cause of rot. Lay the cleaned clumps upside down on a tray or a piece of cardboard in a cool, dry place like a garage or basement. Upside down is important because dahlia stems are hollow; turning them over allows any trapped water to drain out of the stem rather than sitting in the crown.

Let the tubers dry for one to three days. You want the skin to feel dry and slightly firm, but you don't want the tubers to start shriveling. This drying period is called "curing."

If you see any damaged or rotten tubers in the clump, cut them off now with a clean pair of shears. Healthy tubers should feel firm, like a fresh potato. Any part that feels mushy or looks like it is covered in mold should be removed and discarded.

Identifying the Eyes and Dividing

If you want to increase your flower count for next year, you can divide your dahlia clumps in the fall. However, many gardeners find it easier to wait until spring.

The "eyes" of a dahlia are small bumps on the crown of the tuber, similar to the eyes on a potato. In the fall, these can be very hard to see. If you wait until spring, the eyes will begin to swell and turn pink or green, making it very obvious where to cut.

If you are a beginner, we recommend storing the whole clump and dividing it in the spring. This is a safer way to ensure every piece you cut has a viable eye. If a tuber does not have a piece of the crown with an eye attached, it will never grow a new plant, even if the tuber itself looks healthy.

Choosing the Right Storage Container

The goal of storage is to keep the tubers dormant, cool, and just barely moist. If they get too dry, they will shrivel up and die. If they get too wet, they will rot.

The most popular storage method is using a cardboard box or a plastic bin.

• Cardboard boxes: These are great because they allow for a small amount of air exchange.
• Plastic bins: These hold moisture very well, but you must leave the lid slightly ajar or drill small holes in the sides to prevent mold.

Inside the container, you need a packing medium to insulate the tubers. Common choices include:

• Peat moss: This is the most traditional choice. It holds a tiny amount of moisture and is naturally slightly acidic, which helps prevent rot.
• Vermiculite: This is a mineral that does an excellent job of regulating moisture levels.
• Pine shavings: Often sold as animal bedding, these are inexpensive and work well if they are slightly dampened.

Layer the packing material in the bottom of the box, place the tubers on top (making sure they don't touch each other), and then cover them with more material. This prevents a single rotten tuber from spreading the problem to its neighbors.

The Ideal Storage Environment

Where you put your boxes is just as important as how you pack them. The perfect temperature for dahlia storage is between 40°F and 50°F.

A cool, dark basement, a root cellar, or a frost-free garage is usually the best spot. You want to avoid any place that might freeze, as frozen tubers will turn to mush when they thaw. You also want to avoid places that are too warm, like a heated utility room, because the warmth will cause the tubers to wake up too early and start growing in the dark.

Check on your tubers once a month during the winter. This only takes a few minutes but can save your collection. If the tubers look shriveled, lightly mist the packing material with a spray bottle of water. If you see any signs of mold or rot, remove the affected tuber immediately and leave the box open for a day to improve air circulation.

Key Takeaway

• Temperature: Aim for 40°F–50°F.
• Humidity: Keep packing material barely damp, not wet.
• Airflow: Check monthly for rot or shriveling.

Spring Arrival: Bringing Them Back to Life

When the birds start singing and the grass begins to green, it is time to check your dahlias for the upcoming season. In most parts of the country, this happens in April or May. For a step-by-step refresher, see How to Plant Dahlias.

Take the tubers out of their storage boxes and look for signs of life. You should see small, pinkish bumps (the eyes) starting to emerge from the crowns. If you didn't divide your clumps in the fall, now is the perfect time to do it. Use a sharp, clean knife to cut the clump into individual tubers, ensuring each one has at least one eye and a firm body.

If you want to get a head start on the season, you can "wake up" your dahlias indoors about 4 to 6 weeks before your last frost date. Simply plant the tubers in pots with slightly damp potting soil and place them in a warm, sunny window. By the time the weather is warm enough to plant them outside, you will already have several inches of green growth.

Common Myths About Digging Dahlias

There is a lot of advice out there, and not all of it is helpful for the home gardener. Let's clear up a few common misconceptions.

Myth 1: You must wash tubers with bleach before storing. While some professional growers use a very diluted bleach solution to kill bacteria, it isn't necessary for most home gardeners. As long as you remove the soil and let the tubers dry properly, they will store just fine.

Myth 2: If a tuber is shriveled, it is dead. Not necessarily! Some dahlia varieties naturally shrivel more than others. As long as the tuber isn't "crunchy" or completely hollow, it can often be revived. Soaking a slightly shriveled tuber in a bucket of room-temperature water for an hour before planting can often give it the hydration it needs to sprout.

Myth 3: You have to dig them every single year. As we discussed, this depends on your zone. If you are in Zone 8 or 9 and your dahlias are blooming well, you can certainly leave them for two or three years before digging them up to divide the clumps.

Realistic Expectations for Overwintering

It is important to remember that gardening involves nature, and nature is unpredictable. Even with the best care, you might lose a few tubers over the winter. This is a normal part of the process.

Sometimes a tuber is simply too immature to survive storage, or a particular variety is more prone to rot. If you start with 10 tubers and 8 of them survive the winter, you are doing a fantastic job! This is why we often recommend planting a few extra of your favorite varieties, so you always have plenty of color for your garden. Our 100% Quality Guarantee is there if you need support.

Weather variations from year to year will also play a role. A very wet winter might cause losses in the ground that you didn't see the year before. Stay flexible and observe how your specific garden microclimate behaves.

Summary of the Decision Process

Deciding whether to dig is a balance between your climate, your soil, and how much time you want to spend in the garden. For many, the ritual of digging and storing is a peaceful way to close out the gardening year. For others, leaving them in the ground is a way to enjoy a more low-maintenance landscape.

At Longfield Gardens, we want you to feel confident in whichever path you choose. Both methods can lead to a yard filled with incredible, colorful blooms. The most important thing is to get your dahlias through the winter so they can brighten your summer once again.

Summary of Steps

• Identify your zone: Zone 7 and below should almost always dig.
• Check drainage: Wet soil requires digging regardless of temperature.
• Timing: Wait for the first frost to signal dormancy.
• Lifting: Be gentle to protect the necks and eyes.
• Storage: Keep them cool, dark, and slightly moist.

Whether you are growing the classic Thomas Edison or the trendy 'Cafe au Lait', a little bit of winter preparation goes a long way. With the right approach, your dahlia tubers will remain healthy and ready to put on a spectacular show year after year.

FAQ

Can I leave dahlias in the ground in Zone 7?

While Zone 7 is on the edge of dahlia hardiness, it is generally safer to dig them up. A particularly cold winter or a very wet spring can easily kill tubers left outdoors in this zone. If you choose to leave them, you must use a very thick layer of mulch and ensure the soil has excellent drainage.

What happens if I don't dig up my dahlias in a cold climate?

In Zones 6 and colder, dahlia tubers will likely freeze and die if left in the ground. When the water inside the tuber freezes, it expands and ruptures the plant's cells. Once the ground thaws, the tuber will turn into a soft, mushy mess that cannot grow. For more growing advice, see How Hard Is It to Grow Dahlias?.

Do I need to dry my dahlia tubers before storing them?

Yes, curing or drying your tubers for 1 to 3 days is essential. This allows the skin to toughen up and any excess moisture to evaporate from the stems and skin. This simple step significantly reduces the risk of rot and mold during the winter months.

How do I know if a dahlia tuber is still good in the spring?

A healthy tuber should feel firm to the touch, similar to a fresh carrot or potato. In the spring, you should also see "eyes" or small sprouts beginning to form at the crown. If a tuber is mushy, smells bad, or feels completely hollow and brittle, it is no longer viable and should be discarded.