Table of Contents
- Introduction
- Understanding Hardiness Zones and Dahlia Survival
- Why You Might Choose to Dig Up Your Dahlias
- When Is the Best Time to Dig?
- A Step-by-Step Guide to Digging Dahlias
- How to Properly Store Your Dahlia Tubers
- What to Do If You Leave Them in the Ground
- Common Myths About Overwintering Dahlias
- Signs of a Healthy Tuber vs. a Problem Tuber
- Realistic Expectations for Success
- Why Quality Matters from the Start
- Summary of the Decision Process
- Conclusion
- FAQ
Introduction
Dahlias are the undisputed stars of the late-summer garden. Their incredible variety of shapes and colors brings a sense of wonder to any backyard. Whether you love the massive blooms of dinnerplate dahlias or the intricate petals of pompon varieties, these plants offer a rewarding experience for every gardener. At Longfield Gardens, we want to help you enjoy these stunning flowers year after year.
The intricate petals of pompon varieties are another reason gardeners love them.
One of the most common questions we hear as the growing season winds down is whether you should dig up your dahlia tubers. While they are technically tubers, many gardeners call them bulbs. The answer depends on where you live and how you want to manage your garden for the following spring.
This guide will help you decide the best path for your dahlias based on your local climate and soil. We will cover the benefits of lifting your tubers, the risks of leaving them in the ground, and the simple steps for successful winter storage. Our goal is to make your transition into fall gardening smooth and successful.
Key Takeaway: Determining whether to dig up your dahlias depends primarily on your USDA hardiness zone and your soil's drainage.
Understanding Hardiness Zones and Dahlia Survival
The first step in deciding if you should dig up your dahlia tubers is identifying your USDA hardiness zone. Dahlias are native to the warm mountain regions of Mexico and Central America. Because of their tropical origins, they are not naturally equipped to survive deep freezes.
In the United States, dahlias are generally considered hardy in zones 8 through 11. If you live in these warmer regions, your soil rarely freezes deep enough to damage the tubers. In these areas, dahlias can often stay in the ground year-round with minimal extra care.
However, if you live in zones 7 or colder, the winter temperatures will likely drop low enough to freeze the ground. When the water inside a dahlia tuber freezes, it expands and destroys the plant tissue. This results in a mushy, non-viable tuber when the ground thaws in the spring. For gardeners in these northern climates, digging up the tubers is the most reliable way to ensure they return for another season.
The Role of Soil Drainage
Temperature is not the only factor. Soil moisture plays a massive role in whether a dahlia survives the winter. Even in a warm zone 8, dahlia tubers can rot if they sit in cold, soggy soil for several months.
If your garden has heavy clay soil that holds onto water, your dahlias are at a higher risk of rotting. If you have sandy or well-draining soil, the tubers have a much better chance of staying healthy underground. We always recommend evaluating your specific garden spot rather than relying solely on your zone number.
Microclimates in Your Yard
Sometimes, a specific part of your yard might be warmer than the rest. A south-facing flower bed right next to a heated house foundation stays significantly warmer than a bed in the middle of an open lawn. Gardeners often find that dahlias in these "microclimates" survive even in slightly colder zones. If you are on the border of a zone and have a protected spot, you might experiment with leaving a few tubers in the ground while digging up your favorites.
Why You Might Choose to Dig Up Your Dahlias
Even if you live in a climate where dahlias can survive the winter, there are several practical reasons to dig them up and store them indoors. Lifting your tubers is about more than just surviving the cold; it is about maintaining a healthy and manageable garden.
Preventing Rot and Disease
As mentioned, cold and wet soil is the primary enemy of a resting dahlia tuber. By lifting the tubers, you take them out of that high-risk environment. You can control the moisture and temperature in a basement or garage much better than you can control the weather outside. This greatly reduces the chance of losing your plants to fungal issues or rot during a particularly wet winter.
Dividing Your Tubers
Dahlias are incredibly productive. A single tuber planted in the spring will often grow into a large clump of five to ten tubers by the fall. If you leave these clumps in the ground for several years, they become crowded.
Crowded tubers compete for nutrients and water, which can lead to smaller plants and fewer flowers. When you dig them up, you have the opportunity to divide the clump into individual tubers. This gives you more plants to fill your garden or to expand your dahlia collection for free. It is a simple way to expand your flower collection for free.
Organizing Your Garden
Digging up tubers allows you to rethink your garden layout every year. You might decide that a tall cactus dahlia would look better in the back of the bed.
Or you might want to group certain colors together with red dahlias.
Lifting the tubers gives you a "blank slate" each spring, allowing for total creativity in your garden design.
Checking for Pests
Some garden pests, like voles or certain beetle larvae, may feed on tubers during the winter months. By digging them up, you remove the food source and can inspect the tubers for any signs of damage. This helps you identify potential pest problems in your soil before they become a bigger issue the following season.
What to Do Next:
- Check your USDA hardiness zone on a digital map.
- Observe your garden's drainage after a heavy autumn rain.
- Decide if you want to expand your garden by dividing tubers this year.
When Is the Best Time to Dig?
Timing is everything when it comes to lifting dahlias. If you dig too early, the tubers may not have stored enough energy to survive the winter. If you wait too long, a deep freeze could damage them.
Waiting for the First Frost
In most regions, the signal to start digging is the first "killing frost." This is the night when temperatures drop low enough to turn the green foliage of the dahlia black or dark brown. While the top of the plant looks dead, the tubers underground are perfectly safe.
We recommend waiting about a week or two after this first frost before you start digging. During this short waiting period, the tubers go through a final "curing" process. They toughen their skins and prepare for dormancy. This makes them much more durable during the handling and storage process.
The November Rule
If you live in an area that hasn't had a frost by mid-November, you should go ahead and dig them up anyway. You want to get the tubers out of the ground while the soil is still workable and before any sustained, deep freezes arrive. It is much more pleasant to dig in cool autumn weather than in frozen mud or snow.
A Step-by-Step Guide to Digging Dahlias
Digging up dahlias is a straightforward process, but it requires a gentle touch. Dahlia tubers are connected to the main stem by a narrow "neck." If this neck is broken or cracked, the tuber will likely not grow next year.
Step 1: Cut Back the Stems
Before you reach for your shovel, use a pair of clean garden loppers or hand pruners to cut the stems down. Leave about four to six inches of the main stem sticking out of the ground. This "handle" makes the clump easier to locate and gives you something to hold onto while you work.
Step 2: Loosen the Soil
It is best to use a garden fork (also called a pitchfork) rather than a solid spade. A fork is less likely to slice through a tuber hidden underground.
Start digging about 12 inches away from the center of the plant. Sink the fork deep into the soil and gently pry upward. Work your way around the entire plant in a circle, loosening the soil on all sides. You want to lift the entire root ball at once rather than pulling it out of the ground.
Step 3: Lift the Clump
Once the soil is loose, place your hand near the base of the stem handle and use the fork to lever the clump upward. Be very careful not to yank. The weight of the soil can easily snap the fragile tubers away from the stem. Lift the clump and gently shake off the large pieces of dirt.
Step 4: Initial Cleaning
You can use your hands or a small stick to poke away excess soil from between the tubers. Some gardeners prefer to wash their tubers with a garden hose to get them perfectly clean. This makes it easier to see the "eyes" (the small bumps where next year's growth will start).
If you do wash them, ensure they are in a spot with good airflow so they can dry completely. Putting wet tubers into a storage box is an invitation for rot.
Step 5: Curing the Tubers
Before final storage, dahlias need to "cure" for a few days. Place them in a frost-free, shaded area like a garage or a shed. Turn the clumps upside down so any water trapped in the hollow stems can drain out. Allowing the skins to dry and toughen for 24 to 48 hours will help them stay healthy throughout the winter.
Digging Summary:
- Cut stems to 6 inches.
- Dig a wide circle (12 inches out) with a garden fork.
- Lift gently to protect the "necks."
- Clean off soil and let them dry for 1–2 days.
How to Properly Store Your Dahlia Tubers
Successful storage is about finding the right balance of temperature and moisture. You want the tubers to stay dormant and firm without drying out completely or getting so wet that they rot.
Choosing a Storage Container
Common storage options include cardboard boxes, plastic crates, or paper bags. We recommend avoiding airtight plastic containers, as they trap moisture and lead to mold. Cardboard boxes are an excellent choice because they allow for a small amount of air exchange while keeping the tubers dark.
The Packing Medium
To keep the tubers from shriveling, you should surround them with a packing medium. Popular choices include:
- Peat Moss: Holds moisture well but stays fluffy.
- Vermiculite: A mineral that helps regulate moisture perfectly.
- Pine Shavings: Often sold as pet bedding, these are inexpensive and effective.
- Dry Sand: Very traditional, though heavy to move.
Place a layer of your chosen medium in the bottom of the box. Lay the tubers or clumps in a single layer so they aren't touching each other. This prevents a single rotten tuber from spreading issues to the rest of the box. Cover them with more medium and repeat the process if you have multiple layers.
Finding the Perfect Spot
The ideal storage temperature is between 40°F and 50°F.
- Too cold (below 35°F): The tubers may freeze and die.
- Too warm (above 60°F): The tubers may try to wake up and grow or shrivel from moisture loss.
An unheated basement, a crawl space, or an insulated garage is usually the best spot. Keep the boxes off the concrete floor by placing them on a shelf or a wooden pallet. Concrete can draw moisture out of the boxes or become too cold in the dead of winter.
Labeling Is Essential
Dahlia tubers all look very similar once they are out of the ground. If you have several varieties, you must label them. You can write the name of the variety directly on the skin of the tuber with a soft pencil or a permanent marker. Alternatively, tie a tag around the stem handle of the clump. You will be very glad you did this when planting time arrives in the spring!
What to Do If You Leave Them in the Ground
If you live in zone 8 or above, or if you simply want to take a chance in zone 7, you can leave your dahlias in the ground. However, you shouldn't just walk away and leave them to the elements. A little bit of winter preparation goes a long way.
The Power of Mulch
Mulch acts as a blanket for the soil. After the first frost, cut the stems down to about 2 or 3 inches. Cover the entire area with a thick layer of mulch. This could be shredded leaves, straw, or wood chips.
Aim for a layer that is at least 4 to 6 inches deep. This insulation helps keep the soil temperature stable and prevents the ground from freezing as deeply as it would if it were bare.
Managing Moisture
If your winter is particularly wet, you can protect the tubers by placing a piece of plastic or an inverted bucket over the spot where the dahlias are planted. This helps divert heavy rain away from the crown of the plant. Just be sure to remove the cover in early spring so the soil can warm up naturally.
Spring Maintenance
When the weather begins to warm up in the spring, pull back the thick layer of mulch. This allows the sun to hit the soil and wake up the tubers. Keep an eye out for slugs, as they love the cool, damp environment under winter mulch and will happily snack on the tender new dahlia shoots as they emerge.
Common Myths About Overwintering Dahlias
There is a lot of advice on the internet about dahlias, and not all of it is helpful. Let's clarify a few common misconceptions.
Myth: You Must Wash Them with Bleach
Some sources suggest dipping tubers in a bleach solution to prevent rot. We do not recommend this for home gardeners. If you dry your tubers properly and store them in a clean medium, they will stay healthy on their own. Bleach can sometimes damage the delicate "eyes" of the tuber if the concentration is too high.
Myth: You Can't Store Them in Plastic Bags
While airtight plastic is bad, many gardeners have success using plastic grocery bags that are left slightly open. The key is airflow. If you see condensation forming inside a bag, it is too tight and needs more ventilation.
Myth: Shrivelled Tubers Are Dead
In the spring, you might notice your tubers look a bit like wrinkled raisins. This doesn't mean they are dead! As long as the tuber is still firm and not squishy, it is likely just a bit dehydrated. You can soak shriveled tubers in a bucket of room-temperature water for an hour before planting to help them rehydrate.
Signs of a Healthy Tuber vs. a Problem Tuber
Before you put your dahlias away for the winter, it is important to inspect them. You only want to spend energy storing the ones that have a good chance of growing.
The "Squeeze Test"
A healthy tuber should feel firm, like a fresh potato. If you squeeze it and it feels hollow, soft, or "mushy," it is likely rotting from the inside. It is best to compost these tubers now so they don't rot in your storage box.
Checking the Neck
The neck is the narrow part that connects the fat tuber to the main stem. If the neck is broken or hanging by a thread, that specific tuber will not be able to send up a sprout next year. You can trim off broken tubers to keep the rest of the clump tidy.
Looking for the Eye
The eye is a small, slightly raised bump located on the "crown" (the area where the neck meets the stem). Every division must have at least one eye to grow. If you are dividing your clumps in the fall and a piece doesn't have an eye, it won't produce a plant.
Winter Storage Checklist:
- Tubers are dry to the touch.
- Variety names are clearly marked.
- Packed in a breathable medium (peat, shavings, or vermiculite).
- Stored in a cool (40–50°F), dark, frost-free location.
Realistic Expectations for Success
Gardening always involves a bit of cooperation with nature. Even experienced gardeners lose a few tubers over the winter. Factors like unusual temperature spikes, high humidity in your basement, or late-season pests can all affect the outcome.
If you lose a few tubers, don't be discouraged. It is part of the learning process. We suggest checking your stored tubers once a month during the winter. If they look too dry, give the packing medium a very light mist of water. If you see a spot of mold, remove that tuber and increase the airflow in the box. This small bit of attention can make a big difference in your spring success rate.
Why Quality Matters from the Start
Your success in overwintering often starts with the quality of the plants you grow during the summer. Healthy, vigorous plants produce strong, energy-rich tubers that are much more resilient during dormancy.
We work with expert growers to ensure that the dahlias we provide are true to variety and arrive in excellent condition. When you start with premium stock, you give yourself the best possible foundation for a garden that returns year after year.
Summary of the Decision Process
To recap, if you are wondering "should you dig up dahlia bulbs," follow this simple logic:
- Zone 7 and below: Yes, you should dig them up to protect them from freezing.
- Zone 8 and above: You can leave them in, but digging allows for division and prevents rot in wet soil.
- Heavy Clay Soil: Digging is highly recommended to avoid rot, regardless of your zone.
- Limited Space: If you want more plants next year, dig them up so you can divide the clumps.
Conclusion
Deciding whether to dig up your dahlia tubers is a key part of the autumn gardening rhythm. While it requires a bit of effort, the reward is a garden filled with spectacular, familiar favorites every summer. Whether you choose to lift and store them or tuck them in with a thick layer of mulch, your dahlias will appreciate the care you provide.
At Longfield Gardens, we believe that gardening should be a source of joy and relaxation. Taking these simple steps to protect your dahlias ensures that the beauty of your garden continues to grow season after season.
- Identify your hardiness zone to determine your risk level.
- Wait for the first frost to signal the start of the harvest.
- Store tubers in a cool, dark place with a moisture-regulating medium.
Digging up your dahlias is not just about protection; it is an opportunity to refresh your garden and multiply your favorite blooms for the years ahead.
We invite you to explore our selection of dahlias and planning guides to help you create your most beautiful garden yet.
FAQ
Can I dig up my dahlias before the first frost?
Yes, you can dig them up earlier if you need to. However, waiting for the first frost or until mid-November allows the tubers to maximize their energy storage and toughen their skins. If you dig early, be extra careful during the curing process to ensure they don't shrivel.
Do I have to divide the dahlia clumps in the fall?
No, you do not have to divide them right away. Many gardeners prefer to store the entire clump whole and divide them in the spring. Spring division is often easier because the "eyes" become more prominent and easier to see as the weather warms up.
What happens if I forget to dig up my dahlias in a cold zone?
If the ground freezes solid, the tubers will likely turn to mush and will not grow back. If you realize you forgot them and the ground hasn't frozen deep yet, you can try to dig them up immediately or cover the area with a very thick (12-inch) layer of straw to try and save them.
My tubers have a little bit of mold on them in storage. What should I do?
If you see a small amount of surface mold, wipe it off with a dry cloth and increase the airflow in your storage container. If a tuber is soft and rotting, remove it immediately to prevent the rot from spreading to the healthy tubers in the box.