Introduction
There is nothing quite like the peak of dahlia season. As other summer flowers begin to fade, dahlias take center stage with their spectacular colors and intricate shapes. Whether you are growing dinnerplate varieties or petite pompoms, these plants offer a rewarding experience that lasts right up until the first frost. At Longfield Gardens, we want to help you preserve that beauty so you can enjoy the same stunning blooms year after year.
Knowing when do you dig up dahlia bulbs (which are technically tubers) is one of the most important skills for a dahlia lover to master, whether you grow petite pompoms or dinnerplate types. While these plants are tropical at heart, they can easily be saved and replanted if you get the timing right. This guide is designed for home gardeners who want to ensure their tubers stay healthy, firm, and ready for a repeat performance next spring.
By following a few simple steps, you can transition your garden from a summer showstopper to a successful winter rest for dinnerplate dahlias. We will cover the visual cues to look for, how weather affects your timeline, and the best way to handle your tubers once they are out of the ground. Proper timing ensures your dahlias have the energy they need to thrive during their next growing season.
The Best Time to Dig Up Dahlia Tubers
The most common question gardeners ask as autumn approaches is exactly when to start the digging process. While it might be tempting to clear out the garden as soon as the weather turns chilly, patience is a virtue when it comes to dahlias. The tubers spend the final weeks of the season storing energy and maturing, which helps them survive the long winter months in storage.
For most gardeners in the United States, the signal to start digging is the first "killing frost." This occurs when temperatures drop low enough to turn the green foliage of your dahlias brown or black. This visual change might look like the end of the plant, but for the tubers underground, it is actually a vital signal to begin their dormancy.
The First Frost Rule
When a frost hits, the above-ground part of the dahlia plant stops growing. The sudden cold causes the cell walls in the leaves and stems to collapse, which is why they turn dark and wilted so quickly. You do not need to panic the moment you see this change. In fact, many experienced growers wait about a week after the first frost before they start digging.
During this week-long waiting period, the plant goes through a final transition. The nutrients remaining in the stalks move downward into the tubers. This "curing" process in the soil helps the tubers develop a slightly tougher skin, which makes them more resilient against rot and dehydration during winter storage.
Digging Before the Frost
If you live in a region where the growing season is very long or if a hard freeze is predicted to happen suddenly, you might choose to dig before a frost occurs. This is perfectly acceptable, especially if your tubers have been in the ground for at least 120 days. By late October or early November, most tubers are sufficiently mature regardless of whether a frost has touched the leaves.
If you decide to dig before a frost, look for other signs of maturity. The plant may start to lose its vigor, and the lower leaves might begin to yellow naturally. This indicates the plant is already winding down for the season. Digging on a dry, sunny day when the foliage is still green is often much more pleasant for the gardener than working in the cold, wet mud after a freeze.
Key Takeaway: The ideal time to dig is usually 7 to 10 days after the first killing frost has blackened the foliage. This allows the tubers to finish maturing in the soil.
Why Timing Matters for Tubers
Understanding the "why" behind the timing can help you make better decisions for your specific garden. Dahlias are native to the high-altitude regions of Mexico and Central America. In those climates, they don't experience the deep, frozen ground common in many parts of the U.S. Instead, they have a dry season that triggers their rest.
In our gardens, we use the cooling temperatures of autumn to mimic this natural cycle. If you dig too early, the tubers may be small, thin, and watery. These "immature" tubers are much more likely to shrivel up and die during the winter because they haven't built up enough starch reserves or developed a protective skin.
Avoiding the Deep Freeze
While waiting after a frost is beneficial, you must not wait too long. The goal is to get the tubers out of the ground before the soil itself freezes solid. In most areas, a light frost only affects the leaves and stems. However, a hard freeze (temperatures staying well below 32°F for several days) can eventually penetrate the soil.
If the tubers themselves freeze, the cells inside them will burst. When they thaw, they will turn into a soft, mushy mess that cannot be saved. If you see a forecast for a deep, sustained freeze, it is time to get outside and finish your harvest, even if it hasn't been a full week since the foliage died back.
Managing Wet Soil
Soil moisture is another factor that influences your timing. If your autumn has been exceptionally rainy, it may be better to dig your tubers a bit earlier than planned. Tubers sitting in cold, waterlogged soil are prone to rot.
If you have heavy clay soil that holds onto water, try to time your digging for a window of dry weather. Lifting tubers out of dry or slightly damp soil is much easier on the plant—and your back—than pulling them out of heavy, sticky mud. Clean tubers are also much easier to inspect for health and potential storage issues.
Understanding Your Climate and Zone
Your location plays a huge role in determining when do you dig up dahlia bulbs. The USDA Plant Hardiness Zones provide a helpful map for understanding your local climate. At Longfield Gardens, we use these zones to help time our shipments, ensuring your plants arrive when it is safe to put them in the ground.
Zones 3 through 6
In these northern and midwestern regions, the ground will definitely freeze deep enough to kill dahlia tubers. For gardeners in these zones, digging and storing is a mandatory part of the yearly routine. You will likely be digging your tubers in late September or throughout October.
Zone 7
This is often considered a "transition" zone. In a mild winter, dahlia tubers might survive if they are buried deep and covered with a thick layer of mulch (like straw or wood chips). However, since winter weather is unpredictable, most gardeners in Zone 7 still choose to dig their tubers to be safe. It is much better to have them tucked away in a garage than to risk losing a favorite variety to an unexpected cold snap.
Zones 8 and Warmer
If you live in a southern or coastal climate where the ground rarely freezes, you may not need to dig your dahlias at all. You can leave them in the ground as perennials. In these areas, the "digging" time is actually "division" time. Every two or three years, you should still lift the clumps in late winter or early spring to divide them. This prevents the plants from becoming overcrowded, which can lead to smaller blooms and poor air circulation.
What to Do Next:
- Identify your USDA Hardiness Zone to determine if digging is necessary.
- Monitor your local weather forecast starting in late September.
- Gather your supplies (garden fork, labels, and storage boxes) so you are ready when the first frost hits.
How to Dig Dahlias Safely
Once you have determined that the timing is right, the actual process of lifting the tubers requires a gentle touch. Dahlia tubers are connected to the main stem by a narrow "neck." If this neck is bent or broken, the tuber will usually not be able to sprout the following year.
Step 1: Cut Back the Stalks
Before you pick up a shovel, use a pair of clean bypass pruners or loppers to cut the stalks down. Leave about 4 to 6 inches of the stem sticking out of the ground. This serves as a convenient handle and helps you keep track of where the center of the clump is located.
As you cut, you may notice that dahlia stems are hollow. In rainy weather, water can collect inside these hollow stems. Some gardeners like to cover the cut ends with a small piece of aluminum foil if they aren't digging immediately, but this is usually not necessary if you plan to lift them within a few days.
Step 2: Use a Garden Fork
While a shovel can work, a garden fork (often called a pitchfork or digging fork) is the preferred tool for lifting tubers. The tines of a fork are less likely to slice through a tuber than a solid shovel blade.
Start by inserting the fork into the soil about 12 inches away from the main stem. You want to dig a wide circle around the plant. Dahlias can grow quite large underground, and the tubers often spread out further than you might expect. By digging wide, you avoid accidentally spearing the very tubers you are trying to save.
Step 3: Lift with Care
Gently rock the fork back and forth to loosen the soil. Work your way around the entire plant, loosening the earth from all sides. Once the soil feels loose, slide the fork deep under the center of the clump and gently pry it upward.
Avoid the temptation to grab the stem and pull hard. If the soil is still holding onto the tubers, pulling by the stem can snap those fragile necks. Instead, use your hands to clear away loose soil and lift the entire weight of the clump from underneath.
Preparing Tubers for Storage
After the tubers are out of the ground, they need a little bit of preparation before they go into their winter quarters. This process ensures they don't bring pests or diseases into storage and helps them stay hydrated without rotting.
Cleaning the Tubers
There are two schools of thought on cleaning: washing with water or brushing off the dry soil.
- Washing: Using a garden hose to gently wash away the dirt makes it very easy to see the "eyes" (the growth points) and inspect the tubers for damage. However, if you wash them, you must ensure they are 100% dry before you pack them away.
- Brushing: If your soil is sandy and falls away easily, you can simply let the clumps dry for a few hours and then brush off the excess dirt with your hands or a soft brush. This avoids adding extra moisture to the tubers.
If you have heavy clay soil, washing is usually the better option. It is difficult to inspect a tuber that is encased in a hard brick of dried mud.
The Importance of Labeling
This is the step where most gardeners make a mistake. Once the flowers are gone and the stalks are cut, all dahlia clumps look remarkably similar. It is nearly impossible to tell a 'Cafe au Lait' apart from a 'Thomas Edison' once they are out of the dirt.
Use a waterproof garden marker to write the variety name directly on the skin of the largest tuber in the clump. Alternatively, you can use plastic tags or flagging tape tied securely to the stem. Do this immediately as you lift each plant. Don't wait until you have a pile of twenty unlabeled clumps on the lawn!
Curing and Drying
Before packing the tubers into boxes, they need to "cure" for a short period. Place them in a cool, dry area away from direct sunlight and wind. A garage, shed, or basement is perfect. Turn the clumps upside down so any water trapped in the hollow stems can drain out.
Let them sit for 1 to 3 days. The goal is for the exterior skin to feel dry and firm, but the tuber itself should still feel heavy and plump like a potato. Do not let them sit out for weeks, or they will begin to shrivel.
Key Takeaway: Gently lift tubers with a fork, label them immediately, and allow them to dry in a protected area for 24 to 72 hours before final storage.
Creating the Perfect Storage Environment
Success in wintering over dahlias depends on finding the "Goldilocks" environment: not too cold, not too warm, and just the right amount of humidity.
Temperature
The ideal storage temperature is between 40°F and 50°F.
- If the temperature stays above 55°F, the tubers will think it is spring and try to start growing, or they will dry out too quickly.
- If the temperature drops below 35°F, you risk the tubers freezing.
An unheated basement, a crawl space, or an insulated garage are usually the best spots in most homes.
Humidity and Packing Material
Dahlia tubers are mostly water. If the air around them is very dry, they will shrivel up like raisins. To prevent this, most gardeners pack their tubers in a medium that holds a tiny bit of moisture but still allows for air circulation.
Popular packing materials include:
- Coarse Vermiculite: This is many gardeners' top choice because it is sterile and does an excellent job of regulating moisture.
- Pine Wood Shavings: Often sold as animal bedding, these are inexpensive and effective.
- Peat Moss: A classic choice, though it can sometimes be a bit dusty to work with.
- Newspaper: Wrapping individual tubers in several layers of newspaper can also work for smaller collections.
Place a layer of your chosen material in a cardboard box or a plastic bin with a few air holes. Lay the tubers in the box so they aren't touching each other, then cover them with more material.
Common Myths About Digging Dahlias
In the world of gardening, there is plenty of advice passed around that can sometimes make things more complicated than they need to be. Let’s clear up a few common misconceptions.
Myth 1: You Must Divide in the Fall
Many people believe they have to cut their dahlia clumps into individual tubers the moment they dig them up. While some professional growers do this to save space, it is not a requirement for home gardeners. You can store the entire clump exactly as it came out of the ground and wait until spring to divide it. In fact, for beginners, spring division is often easier because the "eyes" (the small bumps where new growth starts) are much more visible after a winter of rest.
Myth 2: You Need Fancy Chemicals
You might hear advice about dipping tubers in fungicides or coating them in wax. For the average home gardener, this is rarely necessary. If you start with healthy plants, clean them properly, and provide a cool, dry storage space, your tubers should store just fine on their own. Simple care beats complicated tricks every time, and Longfield Gardens backs that up with a 100% guarantee.
Myth 3: If a Tuber Shrivels, It Is Dead
If you check your tubers in mid-winter and notice they look a bit wrinkled, don't throw them away! A little bit of shriveling is normal. You can often revive them by lightly misting the packing material with a spray bottle of water. As long as the tuber isn't completely dried out or soft and rotten, it likely still has enough life to grow in the spring.
Troubleshooting Your Harvest
Even with the best timing, you might encounter a few surprises when you dig up your dahlias. Here is how to handle the most common situations.
Small or Thin Tubers
Sometimes you dig up a plant and find only a few tiny, thin tubers instead of a large, beefy clump. This often happens with certain varieties that are naturally poor tuber-makers, or it may happen if the plant was grown in a pot or had a very short growing season. While these small tubers are harder to store because they dry out faster, they can still grow! Pack them extra carefully in vermiculite and check them once a month to ensure they aren't shriveling.
Rot and "Mother Tubers"
When you look at your dahlia clump, you might see one tuber that looks darker, older, and perhaps a bit soft. This is the "mother tuber"—the original one you planted in the spring. It is common for the mother tuber to begin to decompose at the end of the season after it has given its energy to the new plant.
If you see rot on the mother tuber, simply cut it away from the rest of the healthy new tubers. Use a clean, sharp knife and make a clean cut. The rest of the clump will be perfectly fine.
Pests in the Roots
Occasionally, you might find insects like earwigs or slugs hiding in the crevices of the tuber clump. This is another reason why a gentle rinse or a thorough brushing is helpful. Once the tubers are clean and dry, these pests will usually move on, as they prefer the damp environment of the garden over a dry storage box.
Summary of the Fall Dahlia Routine
Gardening is all about timing and observation. By paying attention to the weather and the signals your plants are giving you, you can successfully navigate the transition from autumn to winter.
Lifting your dahlias is a rewarding way to wrap up the season. It gives you a chance to see the hidden progress the plants have made underground and ensures that your favorite variety, Thomas Edison, will return to brighten your yard next year. Whether you are a seasoned pro or a first-time dahlia grower, these steps make the process simple and achievable.
Fall Checklist for Success:
- Wait for the first frost to turn foliage black, then wait 7 more days if weather permits.
- Cut stalks to 6 inches and use a garden fork to lift clumps gently.
- Label each variety immediately.
- Clean and dry tubers in a protected area for 1–3 days.
- Store in a cool (40–50°F) spot packed in vermiculite or wood shavings.
At Longfield Gardens, we believe that every gardener can have success with dahlias. These plants are incredibly resilient, and by getting the timing of your fall harvest right, you are setting the stage for a spectacular display of dinnerplate dahlias next summer. Happy gardening, and enjoy the process of tucking your garden in for its winter nap!
FAQ
How long can dahlia tubers stay in the ground after a frost?
You can safely leave tubers in the ground for about 10 to 14 days after the foliage has died back from a frost. However, you must dig them before the ground freezes solid. If a period of very heavy rain is expected, it is often better to dig them sooner to prevent rot.
Can I dig my dahlias if it hasn't frosted yet?
Yes, you can dig them up if the season is coming to an end and no frost has occurred. If the plants have been growing for at least 4 months, the tubers should be mature enough to store. Some gardeners prefer to dig before the frost to avoid working in cold, muddy conditions.
What happens if I forget to dig up my dahlia bulbs?
In USDA Zones 7 and colder, dahlia tubers left in the ground without significant protection will likely freeze and rot over the winter. They will turn into a soft, jelly-like substance and will not grow back in the spring. In Zone 8 and warmer, they may survive and grow back as perennials.
Should I wash the dirt off the tubers before storing them?
Washing is optional but often helpful. It allows you to see the health of the tubers and identify the eyes more easily. If you do wash them, the most important step is to let them dry completely for a day or two before putting them into storage to prevent mold.
