Table of Contents
- Introduction
- Understanding Your Climate and Hardiness Zone
- Overwintering Dahlias in the Ground (Zones 8-11)
- When to Dig: The First Frost Rule
- Step-by-Step: How to Lift Dahlia Tubers
- Cleaning and Curing Your Tubers
- Choosing the Right Storage Medium
- The Ideal Storage Environment
- Dividing Tubers: Fall vs. Spring
- Troubleshooting Common Winter Issues
- Waking Your Dahlias Up in Spring
- Summary of Success
- FAQ
Introduction
Few things in the garden are as rewarding as a dahlia in full late-summer glory. These plants are the heavy lifters of the fall border, providing buckets of blooms when other perennials begin to fade. If you have fallen in love with a specific variety, you don't have to say goodbye when the season ends. Saving your favorite tubers for next year is a simple, satisfying way to grow your collection, and our dahlia collections are a great place to browse.
At Longfield Gardens, we believe that gardening should be a rewarding experience that builds your confidence every season. Learning how to overwinter your dahlias is a great way to transition from a beginner to a seasoned gardener. It allows you to preserve the "stock" of the varieties you love most while saving money on next year’s garden. For a colorful next-step option, take a look at the Dahlia Assorted Sunlit Jewel Collection.
This guide will walk you through the process of identifying your hardiness zone, preparing your plants for winter, and choosing the storage method that fits your home. Whether you live in a warm climate where dahlias can stay in the ground or a cold region that requires indoor storage, we have you covered. Successfully overwintering dahlias is a straightforward process of timing, proper storage, and a little bit of patience. For more help with winter storage, see How to Care for Dahlia Bulbs Over Winter.
Understanding Your Climate and Hardiness Zone
Before you grab your shovel, the first step is to determine if you even need to dig your dahlias up. Dahlias are native to the high-altitude regions of Mexico and Central America, which means they love warm days and cool (but not freezing) nights. They are not naturally equipped to survive a deep ground freeze. If you're not sure where you fall on the map, check the Hardiness Zone Map.
In the United States, we use USDA Plant Hardiness Zones to determine which plants can survive the winter in a specific area. These zones are based on the average annual minimum winter temperature. Knowing your zone is the simplest way to decide your overwintering strategy.
Zones 8 through 11: Staying in the Ground
If you live in USDA zones 8, 9, 10, or 11, you are in luck. In these warmer climates, the ground rarely freezes deep enough to reach the dahlia tubers. You can usually leave your tubers right where they are. They will enter a dormant state (a period of rest where growth stops) and wait for the warm soil of spring to wake up again.
Zone 7: The Transition Zone
Gardeners in zone 7 are in a "swing" area. In a mild winter, dahlias may survive outdoors if the soil is well-drained and heavily mulched. However, a particularly cold or wet winter can lead to losses. Many gardeners in this zone choose to dig up their most prized varieties just to be safe, while leaving others as an experiment. If you are planning ahead for spring orders, our Shipping Information page explains how timing works by zone.
Zones 3 through 6: The Digging Zones
If you live in zone 6 or colder (including our home base in New Jersey), your dahlias must be dug up and stored indoors. The frozen soil would expand the water inside the tubers, causing them to burst and rot. Fortunately, lifting tubers is a fun fall ritual that signals the end of a successful growing season, and a collection like the Dahlia Assorted Enchantment Collection gives you plenty of favorites worth saving.
Key Takeaway: Always check your USDA hardiness zone before winter. If the ground in your area freezes more than an inch or two deep, indoor storage is the best way to ensure your dahlias return.
Overwintering Dahlias in the Ground (Zones 8-11)
For those in warmer climates, overwintering is less about protecting the plants from cold and more about protecting them from moisture. The biggest threat to a dormant tuber in the ground is "rot," which happens when the soil stays too wet for too long.
Improving Drainage
Before the rainy season begins, ensure your dahlia beds have excellent drainage. Drainage simply refers to how fast water leaves the soil. If you have heavy clay soil that holds onto water like a sponge, your tubers might struggle. You can improve this by planting in raised beds or by adding organic matter to the soil during the growing season.
The Mulching Method
Even in warm zones, a little extra insulation helps. Once the foliage has naturally yellowed or been nipped by a very light frost, cut the stems down to about 3 to 4 inches above the soil. Apply a 3-inch layer of mulch over the top of the plant. Wood chips, straw, or shredded leaves all work well. This layer acts like a blanket, keeping the soil temperature stable and preventing it from becoming oversaturated with winter rain.
What to Do Next in Warm Zones
- Cut back: Remove the old, leafy growth once it turns brown.
- Clean up: Clear away any fallen leaves or debris to prevent pests from nesting.
- Mulch: Apply your protective layer before the coldest month.
- Wait: Leave the tubers alone until new green shoots appear in spring.
For a bright, easy-to-grow mix that fits well in a sunny border, see the Dahlia Decorative Summer Jewels Mix - Bulk Offer.
When to Dig: The First Frost Rule
For gardeners in cold climates, timing is everything. You want to give your dahlias as much time as possible to store energy for next year, but you must get them out of the ground before the soil freezes solid.
The signal to start the process is the first "killing frost." This is a frost that is cold enough to turn the green dahlia foliage black or dark brown. While the top of the plant looks dead, the tubers underground are perfectly fine. In fact, many gardeners believe that a light frost triggers the tubers to go into a deeper dormancy, which helps them store better.
After that first frost, we recommend waiting about 5 to 7 days before digging. This short wait allows the "eyes" (the small bumps where next year’s growth will come from) to become slightly more visible and the skin of the tuber to toughen up. If you expect a week of heavy rain, however, it is better to dig them early to keep the tubers dry.
Step-by-Step: How to Lift Dahlia Tubers
Lifting tubers is an easy afternoon project. You will need a pair of garden pruners, a digging fork (which is better than a shovel because it is less likely to slice through the tubers), and your plant labels.
Step 1: Labeling
This is the most important step. Once the foliage is gone, all tubers look very similar. Use waterproof tags or "surveyor’s tape" to label the stems before you dig. Write the variety name and the color clearly. If you wait until they are in a box, you may forget which is which.
Step 2: Cutting Back
Using sharp pruners, cut the main stem of the dahlia down to about 4 to 6 inches above the ground. Dahlia stems are hollow, so be careful not to let too much water sit inside the "stump" if you aren't digging them immediately.
Step 3: The Wide Circle
Dahlia tuber clumps grow outward like a cluster of sweet potatoes. To avoid damaging them, start digging about 12 inches away from the main stem. Insert your garden fork deep into the soil and gently pry upward. Work your way around the plant in a circle, loosening the soil as you go. For a closer look at tuber structure, see Dahlia Tubers: What You Need to Know.
Step 4: Lifting
Once the soil is loose, reach under the clump with your hands and lift the entire root ball out of the ground. Don't pull by the stem, as the "neck" of the tuber (where it connects to the stem) is very fragile. If the neck breaks, the tuber may not grow next year.
Key Takeaway: Be gentle during the lifting process. A wide digging circle and a light touch will prevent accidental damage to the brittle tubers.
Cleaning and Curing Your Tubers
Once your tubers are out of the ground, they need a little bit of "spa time" before they go into storage. This phase is called curing, and it helps prevent rot and mold.
To Wash or Not to Wash?
There are two schools of thought on cleaning. Some gardeners like to wash every bit of soil off with a garden hose. This makes it easier to see the "eyes" and check for pests. Others prefer to leave a bit of soil on the tubers, believing it provides a natural protective barrier.
If your soil is heavy clay, washing is usually best so you can see what you are doing. If you have light, sandy soil, you can simply shake the clumps gently to remove the excess.
The Drying Phase
After cleaning, move your tubers to a frost-free, shaded area with good airflow. A garage, a shed, or even a porch works well as long as the temperature stays above freezing. Place them upside down (stems pointing toward the ground) on a piece of cardboard or a screen. This allows any moisture trapped inside the hollow stems to drain out.
Let them dry for 1 to 3 days. The skin should feel dry to the touch, and any remaining soil should be crumbly. Do not leave them in direct sunlight, as this can cause the tubers to shrivel.
Choosing the Right Storage Medium
Dahlia tubers are mostly water. The goal of storage is to keep them "sleeping" without letting them dry out completely (shriveling) or stay too wet (rotting). To do this, we use a storage medium to regulate moisture.
Common Storage Materials
- Peat Moss: This is a very popular choice because it holds moisture well but is naturally acidic, which can help prevent some types of mold. Use it slightly damp, but not wet.
- Vermiculite: A mineral that provides excellent aeration. It is very clean and easy to use.
- Pine Wood Shavings: Often sold as animal bedding, these are inexpensive and provide great airflow. They are less likely to hold too much water.
- Potting Soil: If you have extra bags of dry potting mix, this works well for storing whole clumps in large pots.
Containers
You can store your tubers in several types of containers. Plastic storage bins are great for keeping moisture in, but you must leave the lids slightly cracked to allow for airflow. Cardboard boxes are more "breathable" and are a good choice if your storage area is naturally humid. Many gardeners also use large paper bags or even milk crates lined with newspaper.
The Ideal Storage Environment
Location is the most important factor in dahlia survival. You are looking for the "Goldilocks" of environments: not too hot, not too cold, and just the right amount of humidity.
The Temperature Sweet Spot
The ideal temperature for storing dahlia tubers is between 40°F and 50°F.
- If it's too cold (below 32°F): The tubers will freeze, turn to mush, and die.
- If it's too warm (above 55°F): The tubers may try to wake up and start growing, or they may shrivel up because they are losing water too fast.
An unheated basement, a crawl space, or a cool closet in an attached garage are usually the best spots. If you use a garage, keep the boxes off the cold concrete floor by placing them on a wooden pallet or a shelf.
Managing Humidity
Dahlias like about 75% to 85% humidity. If your basement is very dry (which often happens in winter when the heater is running), you might need to mist your storage medium once or twice during the winter. If the area is very damp, you should use a more breathable container like a cardboard box.
Dividing Tubers: Fall vs. Spring
As you look at your dahlia clump, you will notice it is much larger than the single tuber you planted in the spring. You can divide this clump into several individual tubers, each of which will grow into a brand-new plant next year.
Dividing in the Fall
Some gardeners like to divide their tubers immediately after digging. The advantage is that the tubers are softer and easier to cut. It also takes up much less space in storage. The downside is that it can be hard to see the "eyes" (the growth points) in the fall, and you might accidentally cut off a tuber that doesn't have an eye.
Dividing in the Spring
We often recommend waiting until spring to divide, especially for beginners. As the weather warms up, the eyes begin to swell and turn pink or green, making them very easy to see. If you store the whole clump, you have more "insurance" against any single tuber rotting.
Identifying the Eye
A dahlia tuber is only "viable" (able to grow) if it has three parts:
- The Body: The fat part that stores energy.
- The Neck: The thin part connecting the body to the stem.
- The Eye: A small bump on the "crown" (the area where the neck meets the old stem).
If you cut a tuber and it doesn't have an eye, it will never grow a plant, even if the tuber itself looks healthy.
What to Do Next: Monthly Check-ups
- Mark your calendar: Set a reminder to check your tubers once a month.
- Check for rot: If a tuber feels soft or mushy, remove it immediately so the rot doesn't spread.
- Check for shriveling: If the tubers look wrinkled like a raisin, lightly mist the storage medium with water.
- Ventilate: If you see condensation on the inside of a plastic bin, leave the lid off for a day to let it dry out.
Troubleshooting Common Winter Issues
Even with the best care, you might encounter a few hiccups during the winter. Don't worry—most are easy to fix if you catch them early.
Surface Mold
If you see a light, fuzzy white mold on the surface of your tubers, it usually means the air is too still or the medium is a bit too damp. You can gently wipe the mold off with a cloth and increase the airflow in your storage room. Some gardeners use a very diluted solution of water and a splash of vinegar to wipe the tubers down.
Shriveling
A little bit of wrinkling is normal, but if the tubers feel light and hollow, they are dehydrating. This often happens if they are stored in wood shavings in a very dry room. Simply add a small amount of damp peat moss to the container or give the medium a light spray of water.
Early Sprouting
If your tubers start growing long, pale white sprouts in February, your storage area is likely too warm. Move them to a cooler spot. You can snap these early sprouts off; the tuber will usually produce new ones once it is planted in the spring.
Waking Your Dahlias Up in Spring
When the birds start singing and the grass turns green, it’s time to check on your "sleeping" dahlias. About 4 to 6 weeks before the last expected frost, you can bring your tubers out of storage.
The Inspection
Discard any tubers that are completely dried out or mushy. If you haven't divided your clumps yet, this is the perfect time to do it. You will likely see those little pink eyes starting to pop out.
Pre-Starting (Optional)
If you live in a short-summer climate, you can give your dahlias a head start by "potting them up" indoors. Place individual tubers in small pots with damp potting soil and put them in a sunny window or under grow lights. By the time the ground is warm enough to plant outside (usually 60°F), you will have a sturdy plant ready to go. If you want a dramatic spring choice, the Dahlia Dinnerplate Cloud Nine Collection is a standout option.
Planting Out
Wait until all danger of frost has passed before moving your dahlias to the garden. Dahlias love the sun, so choose a spot that gets at least 6 to 8 hours of direct light. Dig a hole about 4 to 6 inches deep, lay the tuber horizontally with the eye pointing up, and cover it with soil. Do not water them until you see the first green shoots emerge, as the tuber has all the moisture it needs to get started. For a deeper look at placement, see How Deep Do I Plant Dahlia Bulbs?.
Summary of Success
Overwintering dahlia tubers is one of the best ways to ensure a spectacular garden year after year. By following these simple steps, you can turn a few favorite plants into a massive collection over time.
- Determine your zone: Only dig if your ground freezes (Zones 3-7).
- Wait for frost: Let the cold trigger dormancy before you lift the tubers.
- Be gentle: Protect the necks and eyes of the tubers during the digging process.
- Dry and cure: Allow the tubers to air dry for a few days before packing.
- Store cool and dark: Aim for 40-50°F in a medium like peat moss or shavings.
- Check often: A quick monthly inspection prevents small issues from becoming big problems.
Longfield Gardens is here to help you every step of the way, from choosing your first tuber to successfully storing it for the next season. We stand behind the quality of our plants and want to see your garden thrive. With a little care this winter, your dahlias will be ready to put on an even bigger show next summer. If you want to keep exploring, our Dahlia Assorted Harvest Collection is another beautiful place to start.
"Saving your dahlia tubers is like putting a little bit of summer in a box. When you open it in the spring, the excitement of a new gardening season begins all over again."
FAQ
Can I store dahlia tubers in the refrigerator?
While a refrigerator is cool, it is usually too dry and often too cold for dahlia tubers. Most home refrigerators are kept below 40°F, which can damage the tubers over a long winter. Additionally, fruit kept in the fridge can release ethylene gas, which may harm the dormant eyes. A cool basement or garage is a much better choice. For a broader overview of dahlia care, see All About Dahlias.
What happens if I don't wait for a frost to dig them up?
You can dig up dahlias before a frost if you need to, but the tubers may not be as hardy. The frost tells the plant to move its energy from the leaves down into the tubers for storage. If you dig too early, the tubers may be smaller and the skin thinner, making them more prone to shriveling during the winter months.
Do I need to treat my tubers with fungicide before storage?
For most home gardeners, a fungicide treatment is not necessary. If you ensure the tubers are dry and cured before packing them in a clean medium, they should stay healthy naturally. If you have had significant rot issues in the past, you can dust the cut ends with sulfur powder, which is a natural mineral that helps prevent fungal growth.
My dahlia tuber broke off the clump without an eye. Will it still grow?
Unfortunately, no. A dahlia tuber is not like a potato; it cannot sprout from just anywhere. It must have a piece of the "crown" (the neck area) where the growth eye is located. If a tuber breaks off mid-neck or is just the fat body, it will eventually rot in the soil because it lacks the genetic material to create a new sprout.