Introduction
There is nothing quite like the late-season firework show that Dinnerplate Dahlias provide in a garden. While other perennials begin to fade and retreat in the cooler air of autumn, dahlias seem to find their second wind, pushing out vibrant, saturated blooms right up until the very end. This spectacular finish is one of the many reasons we love these plants, but it also leads to a common question for home gardeners: how do we transition these beauties from their summer glory into their winter nap? (longfield-gardens.com)
Determining when and how to cut back your plants is the most important part of ensuring they return even stronger next year. At Longfield Gardens, we want to make this process as simple and rewarding as possible. (longfield-gardens.com)
Whether you are a beginner growing your first Cafe au Lait dinnerplate dahlia or a seasoned gardener with a massive collection of cactus varieties and pompon varieties, getting the winter prep right is a major "easy win" for your garden’s future success. (longfield-gardens.com)
This guide will cover the exact timing for cutting back your foliage, the biological reasons why waiting matters, and the step-by-step methods for both digging tubers and overwintering them in the ground. By following a few simple rules, you can protect your tubers and look forward to an even more impressive floral display next summer. When you are ready to shop, browse our Dahlia Collections. (longfield-gardens.com)
The Golden Rule of Timing: Wait for the Frost
The most important tip for cutting back dahlias is also the simplest: wait for the weather to tell you when it is time. In the gardening world, we often talk about "timing beating tricks," and nowhere is this more true than with dahlia care. You should not cut back your dahlias while they are still green and lush, even if the rest of your garden has already been tidied up for the season.
Dahlias are sun-loving plants that use their large leaves as solar panels. Throughout the summer and early fall, those leaves are busy collecting energy and converting it into starches. This energy is then sent down into the tubers below the soil. If you cut the plant back while the foliage is still green, you are essentially cutting off the power supply before the battery is fully charged.
Wait for the first "hard frost." A hard frost is a dip in temperature that is cold enough to actually kill the plant’s top growth. You will know it has happened because your once-beautiful dahlias will turn black or dark brown almost overnight. They may look a bit sad and limp, but this is exactly what you want to see. This blackened foliage is a signal that the plant has officially entered dormancy and has stopped its energy collection for the year.
Why the "Energy Charge" Matters
The energy stored in the tuber during those final weeks of autumn is what fuels the first few weeks of growth next spring. If a tuber is stored with a full "charge," it is much more likely to survive the winter and sprout vigorously when the soil warms up. Furthermore, the period of time between the first frost and the day you cut the stems allows the tuber’s skin to toughen up slightly. This thicker skin acts as a natural barrier against rot and dehydration during the long winter months.
Frost-Free Climates
If you live in a region that does not experience a hard frost, such as parts of the southern United States or coastal California, the timing shifts slightly. In these areas, you should wait until the plant naturally begins to yellow and fade, which usually happens in late November or December. Once the plant looks like it is finished for the season, you can proceed with cutting it back.
Key Takeaway: Always wait for a hard frost to turn the dahlia foliage black before you reach for your pruners. This ensures the tubers have maximum energy for next year’s blooms.
How to Cut Back Your Dahlias: A Step-by-Step Method
Once the frost has done its job and the foliage is dark, it is time to tidy up. You will need a pair of sharp, clean hand pruners or loppers, depending on the thickness of the stems. Some dahlia varieties can produce stems that are over two inches thick, resembling small tree trunks! (longfield-gardens.com)
1. Clean Your Tools
Before you start, wipe your blades with a quick splash of rubbing alcohol or a mild bleach solution. Dahlias can be sensitive to viruses, and cleaning your tools between different plants ensures you don't accidentally spread a problem from one tuber clump to another.
2. Measure Your Cut
Locate the main stem where it meets the ground. You do not want to cut the stem flush with the soil. Instead, leave about 4 to 6 inches of stem protruding from the ground. This "handle" serves several purposes. It marks the location of the tuber if you are leaving it in the ground, and it gives you something to hold onto if you decide to dig the clump up.
3. Clear Away the Debris
After you have cut the stems, remove all the blackened leaves and stalks from the garden bed. It is best to compost this material or dispose of it rather than leaving it to sit on top of the soil. Removing the old foliage helps prevent pests like slugs or earwigs from finding a cozy winter home right on top of your dormant tubers.
4. Deal with Hollow Stems
Dahlia stems are naturally hollow, like a straw. If you cut them back and a heavy rain follows, water can travel down the center of that hollow stem and sit directly on the crown of the tuber. This can lead to rot in very wet winters. If you live in a rainy climate and are leaving your tubers in the ground, you may want to cover the cut ends with a small piece of aluminum foil or flip a small plastic pot over the "stub" to keep the water out.
To Dig or Not to Dig: Knowing Your Zone
Whether you leave the tubers in the garden or bring them inside depends entirely on your local climate and your soil. As we often say, "right plant, right place" also applies to how a plant spends its winter.
Leaving Tubers in the Ground (Zones 8 and Warmer)
If you live in hardiness zones 8, 9, or 10, you are in luck. Your ground likely does not freeze deep enough to damage dahlia tubers. After cutting the plants back to 4–6 inches, simply apply a thick layer of mulch—about 4 to 6 inches of wood chips, straw, or shredded leaves—over the top. This mulch acts as a blanket, keeping the soil temperature stable. We ship our tubers across the country from our facility in Lakewood, New Jersey, and we often see that well-mulched dahlias can survive even in slightly colder Zone 7 if the soil drains very well. (longfield-gardens.com)
Digging and Storing (Zones 6 and Colder)
In most of the United States, winters are too cold for dahlias to survive outside. The water inside the tuber will freeze, causing the cells to burst and the tuber to turn into a mushy mess. For gardeners in these zones, lifting the tubers is the only way to ensure they return.
Even if you live in a warmer zone, you might choose to dig up your tubers every two or three years. This allows you to divide the large clumps, giving you more plants to share with friends or to expand your own garden beds.
Action List: What to do after cutting back
- If in Zone 8+: Apply 4–6 inches of protective mulch.
- If in Zone 6 or colder: Wait 3–7 days after the frost to allow the tubers to "cure," then begin digging.
- Label everything: Use a waterproof marker to write the variety name directly on the tuber or the stem "handle."
- Clean your workspace: Clear all dead foliage to keep the garden tidy and healthy.
The Lifting Process: Gentle and Steady
If you have determined that your tubers need to come inside for the winter, the "lifting" process should be done with care. Dahlia tubers are connected to the central stem by a narrow "neck." If this neck snaps, the tuber will likely not grow, as the "eyes" (the growth points) are located where the neck meets the stem.
Use the Right Tool
Skip the shovel if possible and reach for a sturdy digging fork. A fork allows you to loosen the soil without the risk of slicing right through a tuber. Start your digging at least 12 inches away from the stem. Dahlias grow in a wide, circular clump, and the tubers often extend further than you might expect.
Lift with Care
Push the fork deep into the soil and gently pry upward. Work your way around the entire plant, loosening the soil from all sides. Once the soil is loose, use the stem "handle" to gently lift the entire clump out of the earth. Shake off the excess soil, but do not be aggressive.
The Drying Phase
Before you pack your tubers away, they need to dry out. This is often called "curing." Place the clumps in a frost-free, shaded area like a garage or a porch for 1 to 3 days. You want the outside of the tuber to feel dry to the touch, and any remaining soil should easily crumble away. Avoid leaving them in direct, hot sun, which can cause them to shrivel too much. (longfield-gardens.com)
Winter Storage Strategies
The goal of storage is to keep the tubers in a "Goldilocks" state: not too cold that they freeze, and not too warm that they start growing or rot. The ideal temperature is between 40°F and 50°F.
Choosing a Storage Medium
To prevent the dahlia tubers from drying out completely and becoming shriveled, you should pack them in a material that holds just a tiny bit of moisture. Popular choices include:
- Peat moss: Highly effective but should be used slightly damp, not wet.
- Vermiculite: Great for moisture regulation and very clean to work with.
- Wood shavings: Like the kind used for pet bedding. These provide good air circulation.
- Newspaper: Wrapping individual tubers in paper can work well in higher-humidity basements. (longfield-gardens.com)
Selecting a Container
Cardboard boxes, plastic milk crates, or plastic storage bins are all suitable. If you use plastic bins, do not snap the lid on tight. Tubers are living things and need to breathe. Leave the lid slightly ajar or drill several small holes in the sides of the container to allow for air exchange.
Location Matters
An unheated basement, a root cellar, or a cool crawlspace is usually the best spot. Avoid placing your storage boxes directly on a concrete floor, which can draw out moisture or become too cold. Instead, place them on a shelf or a wooden pallet. Check your tubers once a month during the winter. If you see a soft, rotten spot, cut it away immediately. If the tubers look very wrinkled and dry, give the packing material a light misting with water.
Simple Troubleshooting for Winter Prep
Gardening is a learning process, and every season brings different weather patterns. If things don't go exactly to plan, don't worry—dahlias are remarkably resilient.
"I cut them back before the frost!"
If you accidentally cut your dahlias back while they were still green, they will likely still be okay. They might have slightly less energy stored than they would have otherwise, but most healthy tubers can handle a mistake. Just make sure to get them mulched or dug up quickly so they don't try to send up new green shoots before winter hits.
"My soil is heavy clay and very wet."
In wet, heavy soil, the risk of rot is much higher. Even if you live in a warm Zone 8, you might consider digging your tubers if your garden stays soggy all winter. Drainage is just as important as temperature when it comes to overwintering success.
"I forgot to label them!"
We have all been there. If you have a box of "mystery dahlias," simply store them as usual. When they sprout in the spring, you can treat the first few weeks of growth as a fun surprise. To avoid this next time, try using survey tape or a simple plastic tag tied to the stem before the frost hits.
Preparing for Spring
While the winter may seem long, the time to plant will be here before you know it. We typically begin shipping dahlia tubers from Longfield Gardens in early spring, timed to arrive about two weeks before the ideal planting time for your specific USDA zone. (longfield-gardens.com)
When you pull your stored tubers out of their boxes in the spring, look for the "eyes." These look like tiny bumps or sprouts near the neck of the tuber. If you see these, you know your winter care was a success! If a tuber feels light, hollow, or mushy, it is best to compost it and start fresh with new, high-quality stock. When you are ready to plan ahead, browse our Spring Planted Bulb Collections. (longfield-gardens.com)
"Winterizing dahlias is not about following a strict set of rules, but about listening to your garden. When the frost arrives, it's the plant's way of saying it's ready for a rest. By providing a clean cut and a safe place to sleep, you are setting the stage for a spectacular show next year."
Conclusion
Cutting back your dahlias is the final, satisfying task of the growing season. By waiting for the frost to blacken the foliage, you ensure that your tubers have all the energy they need to produce those massive, colorful blooms we all love. Whether you choose to tuck them in with a heavy layer of mulch or lift them for a cozy winter in the basement, the effort you put in now will be rewarded tenfold when the warm weather returns.
At Longfield Gardens, we stand behind the quality of our plants with a 100% guarantee. We want your gardening journey to be filled with success and joy. If you ever have questions about your dahlias or any other bulbs, our team is here to provide practical support. (longfield-gardens.com)
- Wait for the hard frost to turn foliage black.
- Cut stems to 4–6 inches above the soil line.
- Dig and store in Zones 6 and colder; mulch heavily in Zones 8 and warmer.
- Store in a cool, dark, and ventilated space between 40°F and 50°F.
If you need a quick reference, our FAQs - General Bulbs and Plants cover a lot of common bulb questions. (longfield-gardens.com)
The beauty of gardening lies in the cycle of the seasons. As you put your dahlias to bed this winter, you can already start dreaming of the vibrant colors and lush textures that will fill your yard next summer.
FAQ
Should I wash the dirt off my dahlia tubers before storing them?
While it is tempting to have perfectly clean tubers, it is usually better to leave a little bit of soil on them or only lightly brush it off. Washing them with a hose can introduce too much moisture, which can lead to rot during storage. If you do wash them, ensure they are 100% dry before they go into their winter boxes.
What happens if I cut my dahlias back while they are still green?
Cutting them back while green stops the energy-loading process. While the tubers will usually survive, they may be smaller and have less "fuel" to start growing in the spring. If you must cut them early due to a move or travel, try to leave as much of the stem as possible to keep some energy in the system.
Can I leave my dahlias in their outdoor pots over winter?
If you live in a very warm climate (Zone 9 or 10), you can leave them in pots, but you should move the pots to a sheltered spot where they won't get drenched by winter rain. In colder zones, the soil in a pot freezes much faster and deeper than the ground does. It is best to either bring the entire pot into a frost-free garage or dig the tubers out of the pot and store them in a medium like peat moss.
Is it okay if the dahlia stems are hollow when I cut them?
Yes, dahlia stems are naturally hollow. This is normal for the plant. The only concern with hollow stems is that they can act as a funnel for rainwater. If you are leaving your tubers in the ground in a rainy climate, simply cover the open stem "stubs" with a little mulch or a piece of foil to prevent water from pooling at the base of the plant.
