Introduction
The arrival of autumn often brings a mix of emotions for gardeners. While we enjoy the final, brilliant flush of dahlia blooms in late September, we also know that the first frost is just around the corner. These spectacular flowers are a highlight of the season at Longfield Gardens, and many of us want to ensure our favorite varieties return to brighten the yard next year.
Deciding whether to lift and store your dahlia tubers is one of the most common questions for home gardeners. Because dahlias are tropical plants native to warmer climates, they handle cold weather differently than hardy spring bulbs like tulips or daffodils. This guide will help you determine the best plan for your specific location and provide simple steps for success.
The choice to lift and store your dahlias depends almost entirely on your local winter weather and soil conditions. By understanding your climate and following a few basic steps, you can keep your dahlia collection growing and thriving for years to come.
Understanding Your USDA Hardiness Zone
The first step in deciding if you need to dig up your dahlias is identifying your USDA hardiness zone. Dahlias are considered tender perennials, which means they can live for many years but cannot survive a deep freeze. In the United States, they are generally hardy only in zones 8 through 11.
If you live in zone 8 or warmer, your soil typically does not freeze deep enough to harm the tubers. In these regions, many gardeners choose to leave their dahlias in the ground year-round. However, even in warm zones, heavy winter rains can cause tubers to rot if the soil is dense and holds too much moisture. Successful over-wintering in the ground requires a spot with excellent drainage—meaning the water leaves the soil quickly after it rains.
For those of us in zones 7 and colder, the ground will freeze deep enough to kill the tubers. In these areas, digging them up is a necessary part of the yearly routine if you want to save the plants. While it might seem like a big task, it is actually a rewarding way to see how much your plants have grown and to ensure you have even more blooms next summer.
Why We Dig Up Dahlia Tubers
Beyond just surviving the cold, there are several reasons why lifting your dahlias is a great practice for any gardener. Even if you live in a borderline climate, digging can provide a fresh start for your plants each spring.
Protection from Winter Rot
The primary enemy of a dormant dahlia tuber is moisture. During the winter, the plant is not actively growing or drinking water. If the soil stays cold and soggy for weeks at a time, the tubers can easily rot. By lifting them and storing them in a controlled, dry environment, you eliminate the risk of losing your favorite varieties to wet winter soil.
The Opportunity to Divide
One of the most exciting parts of digging up dahlias is seeing how much the tubers have multiplied. A single tuber planted in May often grows into a large clump containing five to ten new tubers by October. If you leave the clump in the ground for several years, it can become overcrowded. Overcrowding leads to smaller flowers and weaker stems because the plants are competing for nutrients. Digging allows you to divide the clumps, giving you free plants to expand your garden or share with friends.
Better Soil Preparation
When you remove dahlias from a garden bed, it gives you a chance to refresh the soil. You can add compost or organic matter to the area in the late fall or early spring without worrying about disturbing the dormant tubers. This ensures that when you replant in the spring, the soil is nutrient-rich and ready to support those heavy summer blooms.
Key Takeaway: Digging up dahlias isn't just about avoiding the cold; it’s a proactive way to prevent rot, gain new plants through division, and improve your soil quality for the next growing season.
When Is the Right Time to Dig?
Timing is everything when it comes to harvesting 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 "Killing Frost"
The best signal to start digging is the first "killing frost." This is a frost that turns the green foliage of your dahlias black or dark brown. While it might look a bit sad to see your beautiful plants wilt, this is actually a vital part of the plant’s life cycle. When the foliage dies back, the plant sends a final surge of energy down into the tubers, helping them "cure" and prepare for dormancy.
The Curing Period
After the first frost hits, we recommend waiting about 3 to 7 days before you actually start digging. During this week, the eyes on the tubers—the small bumps where next year's stems will grow—often become more prominent and easier to see. This makes the storage and division process much simpler later on. If a hard freeze (temperatures consistently below 28°F) is predicted immediately after the first light frost, you may want to move faster to protect the tubers under the soil.
Monitoring Soil Moisture
If your autumn has been exceptionally rainy, don't wait too long after the frost. Digging in muddy soil is difficult and increases the risk of damaging the fragile "necks" of the tubers. Aim for a day when the soil is moist but not saturated, as the dirt will fall away from the roots more easily.
How to Dig Up Your Dahlias Safely
Digging up tubers requires a gentle touch. Unlike potatoes, which are quite sturdy, dahlia tubers have thin "necks" that connect the body of the tuber to the main stem. If this neck breaks, the tuber will not be able to sprout next year.
Step 1: Cut Back the Stems
Use a pair of clean garden pruners or loppers to cut the stalks down to about 4 to 6 inches above the ground. This remaining bit of stem acts as a handle and helps you keep track of where the center of the clump is located. Dispose of the old foliage in your compost pile, unless the plants showed signs of disease during the summer, in which case it is better to discard them in the trash.
Step 2: Use the Right Tools
A garden fork is generally better than a shovel for lifting dahlias. The tines of a fork are less likely to slice through a tuber than a solid shovel blade. If you only have a shovel, just be extra cautious about your distance from the plant.
Step 3: The Wide Circle Method
Start digging at least 12 inches away from the main stem. Insert your fork deep into the soil and gently pry upward. Work your way around the plant in a circle, loosening the soil from all sides. Once the soil is loose, you can gently lift the entire clump out of the ground. Avoid pulling hard on the stem; instead, lift from underneath the tubers to support their weight.
What to Do Next
- Shake off large clumps of loose soil immediately.
- Check for any tubers that were accidentally sliced; these should be trimmed or discarded as they are prone to rot.
- Label each clump immediately with a waterproof marker or tag so you don't forget which variety is which.
Cleaning and Drying Your Tubers
Once the dahlias are out of the ground, they need a little bit of cleaning before they go into storage. There are two schools of thought on cleaning: washing with water or brushing off dry dirt.
Washing vs. Brushing
Many gardeners prefer to use a garden hose to gently wash the soil off the tubers. This makes it very easy to see the "eyes" and check for any signs of damage or insects. If you choose to wash them, do so gently and avoid using a high-pressure nozzle that could tear the skin.
In very humid climates, or if you don't have a good place for them to dry quickly, you might prefer to let the soil dry on the tubers and then gently brush it off with your hands or a soft brush. This prevents adding extra moisture to the tubers right before storage. At Longfield Gardens, we generally find that washing them makes the spring division process much easier.
The Drying Phase
Regardless of how you clean them, dahlias must be dry before they are packed away. Place the clumps in a frost-free, shaded area with good air circulation—a garage, shed, or basement works well. Turn the clumps upside down so that any water trapped in the hollow stems can drain out. Let them dry for 1 to 3 days. The skin of the tuber should feel dry and slightly toughened, but the tuber itself should still feel firm like a fresh carrot.
Key Takeaway: Proper cleaning and drying are the bridge between the garden and the storage box. Ensuring the tubers are dry to the touch and the stems are drained prevents rot from starting during the winter months.
Storing Dahlias for the Winter
The goal of storage is to keep the tubers dormant: not so cold that they freeze, and not so warm that they start to grow or shrivel up.
Finding the Perfect Spot
The ideal storage temperature is between 40°F and 50°F. For most people, an unheated basement, a crawl space, or a cool closet in a garage stays within this range. Avoid spots near a furnace or water heater, as the air will be too dry and warm. Also, keep them away from exterior walls that might reach freezing temperatures during a cold snap.
Packing Materials
To prevent the tubers from shrivelling, you need to pack them in a material that holds a tiny bit of moisture but stays breathable. Popular choices include:
- Peat Moss: Inexpensive and very effective at regulating moisture.
- Vermiculite: A mineral that provides great insulation and moisture control.
- Wood Shavings: Like the kind used for pet bedding; these allow for excellent airflow.
- Newspaper: You can wrap individual tubers or clumps in several layers of dry newspaper.
Containers
Cardboard boxes, plastic bins with ventilation holes, or even paper grocery bags can be used. If you use plastic bins, do not snap the lid on tight; the tubers are living things and need a small amount of oxygen to survive the winter. Layer the packing material in the bottom, place the tubers inside (making sure they aren't touching each other), and cover them with more material.
Can I Just Leave Them in the Ground?
If you live in a region where the ground only freezes an inch or two deep (typically Zone 7 or 8), you might be tempted to leave your dahlias in place. While this is a gamble, you can increase your chances of success with a few protective steps.
The Mulching Strategy
If you decide to leave them in the ground, cut the stems down to the soil level after the first frost. Cover the entire area with a thick "blanket" of mulch. This could be 6 to 10 inches of straw, shredded leaves, or wood chips. You can even place a piece of plastic or a tarp over the mulch to keep the winter rain from saturating the soil. This helps keep the soil temperature stable and prevents the tubers from rotting.
When to Treat Dahlias as Annuals
For some busy gardeners, the process of digging and storing feels like too much work. It is perfectly okay to treat dahlias as annuals. If you don't have the time or a proper storage space, you can simply leave them in the ground and let nature take its course. In the spring, if they don't sprout, you can enjoy the fun of picking out new dahlia varieties and starting fresh. Gardening should be a joy, not a chore, and choosing to buy new tubers each year is a valid way to enjoy these flowers.
Troubleshooting Common Winter Issues
Even with the best care, sometimes things don't go perfectly. Knowing what to look for can help you save your collection.
Shriveled Tubers
If you check your tubers in mid-winter and they look wrinkled or feel soft, they are losing too much moisture. You can fix this by lightly misting the packing material with a spray bottle. You don't want it wet—just slightly damp to the touch.
Mold or Rot
If you see fuzzy white or gray mold, the storage conditions are too damp or there isn't enough airflow. Remove any tubers that have turned into "mush" immediately so the rot doesn't spread to the healthy ones. Increase the ventilation in your storage container by leaving the lid off or adding more holes.
Early Sprouting
If the storage area is too warm, the tubers might start to grow pale green shoots in February or March. If this happens, try to move them to a cooler spot. You can trim off these early sprouts when you are ready to plant in the spring; the tuber will usually push out a new, stronger eye once it hits the warm soil.
Preparing for Spring Replanting
The reward for your fall efforts comes in the spring. Once the danger of frost has passed and the soil has warmed to about 60°F, you can bring your tubers out of storage.
Checking for Vitality
Healthy tubers will feel firm. Look for the "eyes" near the stem end of the tuber. They look like the eyes on a potato—small, rounded bumps. If you see these, your tuber is ready to grow. If a tuber feels light, hollow, or completely dried out, it likely won't sprout and can be discarded.
Waking Them Up
Some gardeners like to "pre-start" their dahlias indoors in pots about 4 to 6 weeks before the last frost date. This gives you a head start on the season and leads to earlier blooms. If you prefer to keep it simple, you can plant dahlias in spring directly into the garden as soon as the weather is consistently warm.
Conclusion
Deciding whether you need to dig up your dahlia bulbs—or more accurately, their tubers—is a simple matter of matching the plant's needs to your local climate. While those in warmer southern zones can often leave them in the soil with a bit of extra mulch, gardeners in northern climates will find that lifting and storing them is the best way to preserve their favorite blooms.
The process of digging, cleaning, and storing is a wonderful way to connect with the rhythm of the seasons. It turns a single summer of beauty into a multi-year journey of growing and sharing.
- Check your USDA zone to determine if your soil freezes deep in the winter.
- Wait for the first frost to signal the tubers to prepare for dormancy.
- Dig carefully with a garden fork to protect the fragile necks of the tubers.
- Store in a cool, dark, frost-free place in breathable material like peat moss.
As you tuck your dahlias away for their winter nap, remember that this small amount of effort ensures a spectacular show of color next summer. We love helping gardeners succeed, and we invite you to explore the many dahlia collections available at Longfield Gardens when you are ready to expand your collection.
FAQ
Can I leave dahlias in the ground in Zone 7?
It is possible but risky. In Zone 7, a particularly cold winter or a very wet spring can kill the tubers. If you choose to leave them, you must provide a thick layer of mulch (at least 6-8 inches) and ensure the soil has excellent drainage to prevent rot.
What happens if I don't dig up my dahlias in a cold climate?
If the ground freezes where the tubers are located, the water inside the tubers will freeze and expand, turning the tuber into mush once it thaws. The plant will not survive and will not grow back the following spring.
Do I have to wash the dirt off before storing them?
No, it is not strictly necessary. Some gardeners find that leaving a bit of dry soil on the tubers helps protect them from drying out too fast. However, washing makes it easier to spot damage, pests, or the "eyes" needed for dividing.
How long can dahlia tubers stay in the ground after a frost?
You should aim to dig them up within two weeks of the first killing frost. While the tubers are safe as long as the ground isn't frozen solid, waiting too long increases the risk of the tubers starting to rot in cold, wet autumn soil.
