Introduction
As the garden begins to wind down in late September and October, there is often one last, spectacular show of color from the dahlias. These late-season blooms often feel like the most precious ones, signaling the end of a beautiful growing season while reminding us of the varieties we have come to love. At Longfield Gardens, we believe that preserving these favorite flowers is one of the most rewarding parts of being a gardener.
While most people think of spring as the time for propagation, you might find yourself wondering if you can save a piece of that late-season magic before the frost arrives. Perhaps you have a variety that didn’t produce many tubers, or you’ve spotted a "sport"—a branch that has naturally mutated to produce a different, exciting color—that you want to save for next year.
This guide is designed for home gardeners who want to explore the possibilities of autumn propagation. We will cover the specific steps needed to take cuttings in the fall, how to keep those young plants healthy through the winter months, and the best ways to ensure they are ready for the garden come spring. Taking dahlia cuttings in autumn is a simple, effective way to expand your collection with assorted dahlias and safeguard your favorite varieties.
The Short Answer: Yes, You Can
The quick answer is a resounding yes: you can take dahlia cuttings in autumn. While the most common time to take cuttings is in the spring when tubers are just beginning to sprout, autumn cuttings are a fantastic "plan B" for many gardeners. If you want the spring version of this process, see our How to Grow Dahlias from Cuttings guide.
Taking cuttings in the fall is a slightly different process than spring propagation because of the plant’s natural lifecycle. In the spring, the plant is naturally waking up and pushing out new energy. In the autumn, the plant is preparing to go dormant. To succeed with fall cuttings, you have to trick the plant into staying awake and growing throughout the winter.
This method is particularly useful if you have a variety that is known for being a "poor storer." Some dahlias produce thin, spindly tubers that tend to dry out or rot during winter storage. By taking a cutting and keeping it as a living plant indoors, you bypass the risks of tuber storage entirely.
Why Take Cuttings in the Autumn?
Most gardeners are familiar with the standard routine of digging and storing dahlia tubers. However, autumn cuttings offer several unique advantages that make them worth the extra effort of indoor winter care.
Saving a "Sport"
Occasionally, a dahlia plant will produce a branch with a flower that looks completely different from the rest of the plant. This is called a "sport." If you love the look of this accidental mutation, you cannot simply save the tubers from the whole plant, as the tubers will likely revert to the original flower type. Taking a cutting directly from that specific branch is the only way to ensure you preserve that exact mutation.
Protecting Difficult Varieties
Certain dinnerplate varieties are notoriously difficult to overwinter as dormant tubers. Some dinnerplate varieties, for example, may produce huge flowers but very small, fragile tubers. If you have struggled to get a specific variety through the winter in the past, taking a few cuttings in September or October serves as an excellent insurance policy.
Sharing with Friends
Autumn is the time of year when garden tours and plant swaps are most common. If you visit a friend’s garden and fall in love with a specific dahlia, you don't have to wait until they dig their tubers in the winter (and hope they have enough to share). A small snip from a side shoot is often all you need to start your own plant for the following year.
Key Takeaway: Autumn cuttings act as a living insurance policy for your favorite dahlia varieties, especially those that are difficult to store as tubers.
Timing Your Autumn Cuttings
Timing is everything when it comes to successful autumn propagation. You want to take your cuttings while the parent plant is still healthy and actively growing, but before the first hard frost hits.
Once a frost turns the dahlia foliage black, the cells in the stems are damaged, and the chances of a cutting rooting successfully drop significantly. Ideally, you should look for a window of time in late summer or early autumn when the temperatures are starting to cool, but the plants are still vibrant.
In most regions, September and early October are the prime months for this. If you're unsure about timing in your area, the Hardiness Zone Map is a helpful reference. The goal is to give the cuttings enough time to develop a small root system indoors while there is still a decent amount of natural ambient light, even if you plan on using grow lights later.
Essential Tools for the Job
You don't need a professional greenhouse to take dahlia cuttings, but having the right tools on hand will make the process much smoother and more successful.
- A Sharp, Sterile Blade: A clean scalpel or a very sharp craft knife is better than garden shears. Shears can crush the delicate stem tissues, which leads to rot.
- Rooting Hormone: While not strictly necessary, a rooting hormone (in powder or gel form) can speed up the process and help the cutting establish itself faster.
- Rooting Medium: You need a sterile, well-draining material. Many gardeners find success with "rooting plugs" or "cubes," which hold moisture while allowing for plenty of air. Alternatively, a mix of half perlite and half sterile potting soil works well.
- Humidity Dome or Plastic Bags: Young cuttings lose moisture through their leaves very quickly since they don't have roots yet. A clear cover helps keep the air around them humid.
- Grow Lights: This is the most important piece of equipment for autumn cuttings. Because the days are shortening, you must provide artificial light to prevent the plant from trying to go dormant.
How to Select the Best Cutting
Not every part of the dahlia plant is suitable for a cutting. If you pick a stem that is too old or "woody," it will struggle to produce roots. If you pick one that is too soft and watery, it will likely rot before it can grow.
Look for Lateral Shoots
The best cuttings come from "lateral" or side shoots. These are the smaller stems growing out from the leaf axils (the point where a leaf meets the main stem). These shoots are usually more vigorous and have a higher concentration of the natural growth hormones needed for rooting.
The Hollow Stem Rule
Dahlias are famous for having hollow stems, especially the main stalks. However, you want to avoid taking a cutting that has a wide, hollow center at the base. A hollow stem is a magnet for bacteria and fungus, which causes the cutting to turn black and mushy. Try to cut as close to a "node" (the bump on the stem where leaves emerge) as possible, as the stem is usually solid at that point.
Health Check
Only take cuttings from plants that look healthy. Avoid any stems that show signs of powdery mildew, spotting, or insect damage. Since you will be bringing these plants indoors for several months, you don't want to accidentally invite pests like spider mites or aphids into your home.
What to do next:
- Inspect your dahlia plants for vigorous side shoots.
- Sanitize your cutting tool with rubbing alcohol.
- Prepare your rooting medium by pre-moistening it.
For a broader refresher on the basics, see our How to Take Dahlia Cuttings From Plants guide.
Step-by-Step: Taking the Cutting
Once you have identified a healthy side shoot that is about 3 to 4 inches long, it is time to make the cut.
- Make the Cut: Use your sharp blade to slice the side shoot away from the main plant. Aim to cut just below a leaf node.
- Trim the Foliage: Remove the bottom set of leaves entirely. This exposes the nodes where the new roots will eventually emerge. If the remaining leaves at the top are very large, you can actually cut them in half horizontally. This reduces the surface area, which helps the plant retain moisture.
- Apply Rooting Hormone: Dip the bottom inch of the stem into your rooting hormone. Tap off any excess; a little goes a long way.
- Insert into Medium: Use a pencil or a small stick to poke a hole in your rooting medium. This ensures that the rooting hormone isn't wiped off the stem as you push it into the soil. Gently firm the medium around the stem.
- Provide Humidity: Place your cuttings under a humidity dome or inside a clear plastic bag. Make sure the leaves aren't touching the sides of the plastic, as the condensation can cause leaf rot.
The Secret to Winter Success: Light and Temperature
Taking the cutting is the easy part. The real challenge—and the reason most people fail with autumn cuttings—is keeping them alive through the dark days of winter. For more general care tips, our How to Best Grow Dahlias guide covers the basics from planting to feeding.
Why Lights are Non-Negotiable
In the autumn, dahlias naturally react to shorter days by sending all their energy into their tubers for dormancy. If you place your cuttings on a windowsill, even a south-facing one, they will likely sense the short day-length and stop growing. They might even try to form a tiny "pea-sized" tuber and then die back.
To prevent this, you must provide at least 14 to 16 hours of light per day. Standard LED shop lights or specialized grow lights work perfectly. Keep the lights about 4 to 6 inches above the tops of the plants. This constant light cycle "tricks" the dahlia into thinking it is still summer, keeping it in a state of active green growth.
Temperature Control
Dahlia cuttings prefer a consistent temperature between 65°F and 75°F. If the area is too cold (like an unheated garage or a drafty basement), the roots will grow very slowly, and the plant will be more susceptible to rot. A seedling heat mat placed under the propagation tray can be very helpful during the first two weeks while roots are forming.
Airflow
While humidity is essential for the first 10 days, once the cuttings have established roots, you should gradually remove the humidity dome. Good airflow is vital to prevent fungal issues like "damping off" or powdery mildew. A small fan moving air gently around the room can make a world of difference.
Transitioning Cuttings to Pots
In about two to three weeks, you can gently tug on your cuttings. If you feel resistance, it means roots have formed. Once the roots are about an inch long, it is time to move them from their rooting medium into small individual pots (around 3 to 4 inches in diameter) filled with high-quality potting soil.
Be very gentle during this transition. Dahlia roots at this stage are incredibly fragile—they look like fine white threads and can snap easily. Once they are potted up, you can begin a very light fertilization routine. Use a balanced, water-soluble fertilizer diluted to half-strength once every two weeks.
Managing Growth Until Spring
By mid-winter, your autumn cuttings might start to look like miniature versions of the plants you had in the garden. Because they are growing in limited soil under artificial light, they may become "leggy" or tall and thin. If you need a refresher, see How to Pinch and Stake Dahlias.
Pinching Back
Don't be afraid to pinch your indoor dahlias. Once the plant has four sets of leaves, snip off the very top growing tip. This encourages the plant to branch out and become bushy rather than tall and floppy. These pinched-off tops can actually be used as second cuttings if you want to further increase your stock!
Monitoring for Pests
Indoor environments are the perfect breeding ground for common pests like spider mites or fungus gnats. Check the undersides of the leaves regularly. If you see tiny webs or small spots, treat the plants with a gentle insecticidal soap or neem oil, following the label instructions carefully.
Watering Correctly
Watering is a balancing act. You want the soil to stay moist but never soggy. Wait until the top inch of soil feels dry to the touch before watering again. If the pots sit in water, the young roots will quickly suffocate and rot.
Moving Back to the Garden
As spring approaches and the threat of frost passes, it is time to prepare your plants for the great outdoors. This process is known as "hardening off."
Your indoor plants have lived a very pampered life with consistent temperatures and artificial light. If you move them directly into the hot sun and wind of the garden, they will go into shock.
- Week 1: Move the pots outside to a shaded, protected spot for one hour, then bring them back inside.
- Week 2: Gradually increase the time outdoors and the exposure to sunlight each day.
- Week 3: By now, the plants should be able to spend the whole day and night outside, provided there is no frost in the forecast.
When you finally plant them in the ground, they will already have a head start over the dahlias being planted as dormant tubers. You can expect flowers much earlier in the season from these "overwintered" cuttings.
Key Takeaway: The key to autumn cutting success is providing 14+ hours of light to prevent dormancy and carefully hardening off the plants in spring.
Troubleshooting Common Issues
Even with the best care, you might run into a few hurdles. Here is how to handle the most common issues with autumn propagation.
Cuttings Wilting Immediately
If your cutting wilts within hours of being taken, it is likely losing moisture faster than it can take it up. Ensure your humidity dome is tight and that the leaves have been trimmed to reduce surface area. You can also try misting the leaves with a spray bottle once a day.
Stems Turning Black at the Base
This is usually a sign of rot caused by bacteria or a medium that is too wet. Make sure your tools are sterile and that you are using a light, airy rooting medium. If a stem turns black, it is best to discard it and the surrounding soil to prevent the spread to other cuttings.
Yellowing Leaves
If the lower leaves of your established cutting start to turn yellow, the plant might need a bit of food. Start a low-dose liquid fertilizer routine. Yellowing can also be a sign of overwatering, so check the moisture level of the soil before feeding.
Slow Growth
In the dead of winter (January and February), growth may slow down naturally. As long as the plant looks green and healthy, don't worry. As the natural light through the windows begins to increase in March, you will see the plants pick up speed again.
Conclusion
Taking dahlia cuttings in the autumn is a rewarding way to extend your gardening season and ensure your favorite varieties return year after year. It transforms the potential "loss" of a tender variety into a collection of healthy, vigorous new plants. While it requires a bit more commitment than simply storing tubers, the reward of seeing those early summer blooms makes every bit of effort worthwhile. To keep building your own plant list, browse our dahlia collections.
Whether you are saving a rare sport, preserving a fragile variety, or simply wanting more flowers for your garden, autumn propagation is a skill that every dahlia lover should have in their toolkit. We at Longfield Gardens are always here to help you grow a more beautiful garden, whether that means browsing our best-selling dahlias or using the practical advice you need for year-round success.
- Select healthy side shoots before the first frost.
- Use sterile tools and a well-draining rooting medium.
- Provide 14–16 hours of light to keep the plants from going dormant.
- Harden off plants gradually in the spring for the best results.
"Gardening is a cycle of constant learning and growth. By taking autumn cuttings, you are not just saving a plant; you are participating in the wonderful continuity of the garden season."
We invite you to explore our big blooms and other perennials at Longfield Gardens to find your next favorite variety to propagate and enjoy.
FAQ
Can I root dahlia cuttings in water during the autumn?
Yes, you can root dahlia cuttings in water, though the success rate is sometimes lower than using a solid medium. Place the cutting in a clean jar with about an inch of water, ensuring no leaves are submerged. Change the water every few days to keep it fresh. Once roots are about an inch long, carefully transplant the cutting into potting soil, as "water roots" are very fragile.
Do I need to dig up the tubers if I’ve taken cuttings?
You should still dig and store the parent tubers if you live in a climate where the ground freezes. The cuttings serve as a backup and a way to increase your plant count, but the original tuber is still a valuable asset. If the cuttings thrive, you’ll have extra plants; if the tubers rot in storage, the cuttings will save the variety for you. For more details, see How to Lift and Store Dahlia Bulbs.
How big will the autumn cuttings get by springtime?
If given enough light and a few pot upgrades, an autumn cutting can grow into a 1-to-2-foot-tall bushy plant by May. It is important to keep them in appropriately sized pots; if they become "root-bound" (where roots circle the inside of the pot), their growth may be stunted. Pinching the tops will help keep the size manageable while creating a fuller plant.
Will autumn cuttings produce flowers in their first year?
Yes, dahlia cuttings taken in autumn and grown through the winter will bloom in their first summer. In fact, because they already have an established root system and green growth when they are planted out, they often bloom several weeks earlier than dahlias grown from tubers planted at the same time. They will also develop their own set of tubers by the end of the following autumn.
