Introduction
There is a unique sense of pride that comes with growing dahlias. These garden stars offer some of the most spectacular colors and intricate shapes in the floral world, often blooming their hearts out from midsummer right through the first chilly days of autumn. Whether you are growing dinnerplate varieties the size of a dessert plate or charming pompons, the joy of harvesting a fresh bouquet from your own backyard never gets old.
At Longfield Gardens, we want to help you enjoy those beautiful blooms year after year. While dahlias are treated as annuals in many parts of the country, they are actually tender perennials. This means that with a little bit of simple end-of-season care, you can save the underground tubers and replant them next spring.
Knowing exactly when to remove your dahlia tubers—often called bulbs by many gardeners—from the ground is the most important part of this process. This guide will help you identify the perfect timing based on your local weather, explain the signs your plants are giving you, and walk you through the simple steps to transition your garden for the winter. By getting the timing right, you ensure your dahlias have the best chance of a restful winter and a vigorous return next season.
Understanding the Dahlia Lifecycle
To understand when to dig, it helps to know what is happening beneath the soil. Dahlias grow from tubers, which are fleshy, underground storage organs. These tubers act like a battery, storing energy in the form of starches to fuel next year's growth.
Throughout the summer, the plant uses most of its energy to produce stems, leaves, and those famous flowers. As the days grow shorter and the temperatures begin to drop, the plant’s focus shifts. It stops prioritizing new blooms and starts sending all its remaining energy down into the tubers.
This process of "bulking up" is essential. The more energy the tuber stores, the better it will perform when you wake it up in the spring. If you dig too early, the tubers may be thin and shriveled, making them less likely to survive the winter in storage.
The Role of the First Frost
For most gardeners in the United States, the "first frost" is the most reliable signal that it is time to start thinking about digging. A frost occurs when the air temperature drops to 32°F or lower, causing ice crystals to form on the plant's surface.
Dahlias are native to the warm climates of Mexico and Central America, so they have no natural defense against freezing temperatures. When a light frost hits, the foliage and stems will quickly turn from vibrant green to a dark brown or black. While this might look a bit sad at first glance, it is actually exactly what we want to see.
This blackened foliage is the plant's way of telling you that its work above ground is finished. Once the top growth dies back, the plant enters a period of dormancy, or a "winter nap." This is the signal that the tubers are mature and ready to be moved.
Key Takeaway: The best time to remove dahlia tubers is shortly after the first frost has turned the foliage black or dark brown.
Do You Have to Wait for Frost?
While waiting for a frost is the traditional method, it is not a strict requirement. Some gardeners live in areas where a hard frost doesn't arrive until very late in the year, or perhaps they need to clear their garden beds earlier to make room for fall cleanup.
If your local weather forecast remains warm but you are ready to put your garden to bed, you can manually trigger the dormancy process. You can do this by cutting the plants down to about 4 to 6 inches above the soil line.
After cutting them back, leave the tubers in the ground for about 10 to 14 days. This "curing" time in the soil allows the skin of the tubers to toughen up and helps the "eyes"—the small bumps where next year’s stems will grow—become more visible.
The Two-Week Rule: Patience Pays Off
After the first frost hits and your dahlia plants look like they have melted, it is tempting to run out with a shovel immediately. However, many experienced growers recommend waiting about a week or two before actually lifting the tubers from the dirt.
During this brief waiting period, the tubers undergo a final stage of maturation. They absorb the remaining nutrients from the stems and the skin begins to set. This makes them more durable and less prone to nicks and scratches during the digging process.
However, keep a close eye on the weather during this two-week window. You want the tubers to stay in the ground while the air is cold, but you do not want the ground itself to freeze.
The "Hard Freeze" Deadline
There is a big difference between a light frost and a hard freeze. A light frost only affects the leaves and soft stems. A hard freeze occurs when temperatures drop significantly below 32°F for several hours, causing the soil itself to begin freezing.
You must remove your dahlia tubers before the ground freezes solid. If the soil freezes, the water inside the dahlia tubers will also freeze. Because water expands when it turns to ice, it will rupture the cells of the tuber, turning it into a mushy, rotten mess that cannot be saved.
If you see a forecast for several nights of temperatures in the mid-20s, that is your signal to get out into the garden and start digging, even if you haven't reached the full two-week waiting period.
What to do next:
- Monitor your local weather forecast starting in late September.
- Identify your average first frost date so you can prepare your supplies.
- Watch for the foliage to turn black after a chilly night.
- Aim to dig within 7 to 14 days after that frost, but always before a deep ground freeze.
How Your USDA Hardiness Zone Affects Timing
Your geographic location plays the biggest role in determining your dahlia schedule. Since the United States has a wide variety of climates, the "when" will look different for everyone.
Northern Climates (Zones 3-6)
In these regions, the first frost often arrives in late September or October. The growing season is shorter, so it is vital to let the plants grow as long as possible to ensure the tubers are large enough to store. Gardeners here almost always need to dig and store their dahlias indoors.
Middle Climates (Zone 7)
Zone 7 is a "swing" zone. Depending on the year, a thick layer of mulch (like straw or wood chips) might be enough to protect dahlias through the winter. However, most gardeners find it safer to dig them up, especially if the winter is expected to be wet. Wet, cold soil is often more dangerous to dahlias than the cold air itself.
Southern and Coastal Climates (Zones 8-11)
In these warmer areas, dahlias can often stay in the ground all year. They will naturally go dormant as the days shorten. Instead of digging them up, you can simply cut the dead foliage back and let them rest. We recommend adding a layer of mulch to keep the soil temperature stable and prevent the tubers from rotting during winter rains.
Preparing to Remove the Tubers
Once you have determined that the timing is right, you need to prepare the plants for removal. Preparation makes the job easier and protects the health of the tubers.
First, cut the stems down. Use a pair of sharp, clean pruners or loppers to cut the main stalk, leaving about 4 to 6 inches of stem protruding from the ground. This remaining stem acts as a convenient handle and helps you locate the center of the tuber clump.
It is a good idea to sanitize your cutting tools with a simple solution of isopropyl alcohol or a mild bleach-water mix between plants. This prevents the spread of any soil-borne diseases from one dahlia to the next.
Labeling: The Step You Shouldn't Skip
The moment you cut those stems, all your dahlias will start to look the same. To avoid a "mystery garden" next year, label your plants before you dig them up.
You can use waterproof garden markers or flagging tape tied around the remaining stem. Write the variety name and the color clearly. Some gardeners even write the name directly on the skin of the tuber with a soft pencil or permanent marker once they are cleaned, but labeling the stems in the field is the best first step.
Key Takeaway: Always label your dahlias before or during the digging process to ensure you know which variety is which for next season.
Lifting the Tubers Gently
When the time is right, you’ll need a garden fork or a sturdy shovel. A garden fork is often preferred because it is less likely to slice through a tuber than a solid spade blade.
Dahlia tuber clumps can grow surprisingly wide over a single season. To avoid damage, start digging about 12 inches away from the main stem. Gently loosen the soil all the way around the plant before attempting to lift it.
Once the soil is loose, slide your fork under the clump and use the handle as a lever to gently pry the tubers upward. Use the stem "handle" you left behind to help guide the clump out of the earth. Be very gentle during this stage; the "necks" of the tubers—the narrow part where they attach to the main stem—are quite fragile and can snap easily.
Cleaning and Curing After Removal
Once the tubers are out of the ground, they need a bit of attention before they go into storage.
Start by gently shaking off the large clumps of loose soil. Some gardeners prefer to wash their tubers with a garden hose to remove all the dirt. This makes it much easier to see the "eyes" and check for any signs of rot or damage. If you do wash them, be sure to do it gently so you don't nick the skin.
After cleaning, the tubers need to dry, or cure. Place them in a frost-free, shaded area with good air circulation for 1 to 3 days. A garage or a covered porch works well. Turn the clumps upside down so that any water trapped in the hollow stems can drain out. This step is crucial for preventing crown rot during the winter.
What to do next:
- Cut stems to 4-6 inches and sanitize your tools.
- Label each plant clearly before lifting.
- Dig wide around the plant to avoid tuber damage.
- Allow tubers to dry upside down in a protected area for a few days.
Assessing Tuber Health
As you are cleaning and drying your tubers, take a moment to look them over. Not every tuber in a clump will be a winner, and that’s perfectly okay.
Look for tubers that feel firm to the touch, similar to a fresh potato. If you find any that are mushy, shriveled, or have obvious signs of mold, it is best to trim them off and discard them. You only want to keep the healthiest pieces for storage.
If you see any thin, "hairy" roots hanging off the main tubers, you can trim those back with scissors. They don't provide any benefit during storage and can sometimes hold onto excess moisture that leads to decay.
To Divide or Not to Divide?
One common question gardeners ask when removing dahlias is whether they should divide the clumps into individual tubers in the fall or wait until the spring.
Dividing in the Fall
Dividing now takes up less storage space. The tubers are also softer and easier to cut in the autumn. However, it can be harder to see the "eyes" (the growth points) right after digging.
Dividing in the Spring
Waiting until spring allows the eyes to begin swelling, making it very obvious where to make your cuts. The downside is that the tubers become much tougher over the winter, often requiring more effort to slice through the woody center of the clump.
There is no wrong answer here. If you are a beginner, we often recommend keeping the clumps whole or only doing a rough division until you get more comfortable identifying the growth points.
Storing Your Dahlias for Winter
Once your tubers are removed, cleaned, and cured, they are ready for their winter home. The goal of storage is to keep the tubers cool enough to stay dormant, but not so cold that they freeze.
The ideal temperature for storage is between 40°F and 50°F. A cool basement, an unheated crawl space, or a corner of a garage that stays above freezing are all good options.
To prevent the tubers from drying out completely, we recommend packing them in a breathable material. You can use:
- Unscented wood shavings (often sold as animal bedding)
- Coarse vermiculite
- Dry peat moss
- Slightly damp sand
Place a layer of your chosen material in a cardboard box or a plastic bin with ventilation holes, lay the tubers inside so they aren't touching each other, and cover them with more material. This "insulation" helps maintain a consistent humidity level.
Realistic Expectations for Overwintering
It is important to remember that gardening is a partnership with nature, and nature can be unpredictable. Even with perfect timing and care, it is normal to lose a few tubers during the winter storage process.
Factors like the humidity in your basement, the health of the plant during the summer, and the specific dahlia varieties can all play a role. Some varieties are naturally "great keepers," while others are a bit more delicate.
Checking on your stored tubers once a month is a great habit. If you see a tuber starting to rot, remove it immediately so the problem doesn't spread to the rest of the box. If they look very shriveled and dry, a light misting of water can help rehydrate them.
Summary of the "When"
If you find yourself wondering "when should I remove dahlia bulbs from the ground," simply remember these three signals:
- The Visual Signal: The foliage turns black after the first frost.
- The Maturation Signal: Wait 7 to 14 days after the frost (if weather permits).
- The Deadline Signal: Dig before the thermometer stays below freezing and the ground hardens.
Conclusion
Dahlias are a rewarding investment in your garden's beauty. By paying close attention to the changing seasons and responding to the cues your plants provide, you can successfully preserve your favorite varieties for years to come. Removing them at the right time is the best way to honor the hard work the plants did all summer long.
Our team at Longfield Gardens is always here to support your gardening journey. Whether you are expanding your collection with new colors or perfecting your winter storage technique, the most important thing is to enjoy the process. Gardening is a continuous cycle of growth, and there is nothing quite like the excitement of seeing those first green shoots emerge from your saved tubers in the spring.
Key Takeaway: Timing your dahlia harvest with the first frost ensures mature, healthy tubers that are ready to thrive again next year.
For more inspiration and a wide selection of premium dahlia varieties to add to your garden, visit us and explore our planning guides and bulk buys.
FAQ
Can I dig up my dahlias before the first frost if I'm going on vacation?
Yes, you can dig them up before a frost if necessary. To ensure they are ready, cut the stems down to about 6 inches and leave them in the ground for about 10 days before lifting. This helps the tubers enter dormancy and toughens the skin for storage.
What happens if I forget to dig my dahlias and the ground freezes?
If the ground freezes solid, the tubers will likely freeze as well. Once thawed, they will become soft and rot. If you've had a sudden freeze, dig them up immediately to check their condition. If they are still firm, they might have survived, but if they are mushy, they unfortunately cannot be saved.
Should I wash the dirt off the tubers or just brush it off?
Both methods work. Brushing off loose soil is faster and avoids adding moisture. However, washing them with a hose allows you to see the "eyes" and check for damage more clearly. If you choose to wash them, make sure they dry completely in a protected area for a few days before you pack them away.
Do I need to dig up my dahlias if I live in a warm climate like Florida or Southern California?
In USDA Zones 8 through 11, you generally do not need to remove dahlia tubers from the ground. You can simply cut back the dead stems and leave the tubers to rest. However, if your soil is very heavy and holds a lot of water during winter rains, you may still want to dig them up to prevent rot.
