Introduction
There is a unique kind of excitement that comes with digging up dahlias at the end of a successful growing season. After months of enjoying those spectacular, dinnerplate dahlias and vibrant colors, finding a massive clump of tubers beneath the soil feels like discovering buried treasure. It is one of the most rewarding moments for any gardener because those tubers represent the promise of even more flowers next year.
At Longfield Gardens, we believe that understanding your plants is the best way to ensure they thrive year after year. While a large clump of tubers looks impressive, it often leads to the question: should you split dahlia tubers or plant the whole clump again? Splitting may seem a bit technical at first, but it is a straightforward process that helps your plants stay healthy and gives you plenty of extra tubers to expand your garden with dahlia collections.
In this guide, we will walk you through the reasons for dividing your dahlias, the best time to do it, and the simple steps to ensure every piece you cut has the potential to grow. Mastering this skill is a great way to take your gardening to the next level. Dividing dahlia tubers is a practical and satisfying task that ensures your summer garden remains a productive, blooming paradise.
Why You Should Split Dahlia Tubers
The decision to split dahlia tubers usually comes down to three main goals: plant health, flower quality, and garden expansion. While it might be tempting to simply store the entire clump and replant it in the spring, taking the time to divide them offers several significant advantages.
Preventing Overcrowding and Disease
When a dahlia clump grows too large, it produces an abundance of stems. While this might sound like a good thing, a plant with too many stalks often becomes overcrowded. This thick growth can restrict airflow around the base of the plant, creating a humid environment where powdery mildew and other fungal issues can thrive. By splitting the tubers, you ensure that each new plant has a manageable number of stems, which improves air circulation and keeps the foliage healthy.
Maintaining Flower Production
A massive clump of tubers has a huge amount of stored energy, but it also has many "eyes" or growth points. If you plant the whole clump, the plant may focus its energy on producing leaves and stems rather than the large, showy flowers you love. Smaller, divided sections usually produce more vigorous plants that prioritize bloom production. Over time, undivided clumps can also become "woody" or less productive. Dividing them every year or two keeps the stock young and energetic.
Multiplying Your Collection
One of the best parts of growing dahlias is the math. A single tuber planted in May can easily turn into a clump of five to ten viable tubers by October. Splitting allows you to turn one "Cafe au Lait" dahlia into a whole row of them. It is an easy, cost-effective way to fill your garden with your favorite varieties and browse our dahlia collections.
Better Storage Success
Large clumps are often harder to store than individual tubers. They take up more space and can trap moisture or soil in the center of the clump, which may lead to rot during the winter months. Splitting and cleaning the tubers before storage makes it easier to inspect each piece for damage and ensures you only keep the healthiest stock.
Key Takeaway: Splitting dahlia tubers prevents overcrowding, encourages better flower production, and allows you to grow your flower collection for free.
Understanding the Anatomy of a Dahlia Tuber
Before you pick up your snips, it helps to know exactly what you are looking at. A dahlia tuber is not like a potato; you cannot just cut it into random chunks and expect them to grow. For a dahlia tuber to be "viable"—meaning it can grow into a plant—it must have three specific parts.
The Body
The body is the thick, starchy part of the tuber. This is the plant's pantry. It stores the water and nutrients the dahlia needs to start growing in the spring before it develops a full root system. Bodies come in many shapes and sizes. Some varieties produce long, skinny tubers, while others produce short, round ones.
The Neck
The neck is the narrow part that connects the body of the tuber to the main stem or crown. This is the most fragile part of the tuber. If the neck is bent, cracked, or broken, the energy in the body cannot reach the growth point, and the tuber will not grow. Handle your tubers gently to keep these "necks" intact.
The Crown and the Eye
The crown is the area where the neck meets the base of last year’s stalk. This is the most important part because it contains the "eyes." An eye is a small, slightly raised bump that looks like the eye on a potato. This is the bud that will eventually become next year's stem.
If a tuber breaks off and does not have a piece of the crown with at least one eye attached, it will never grow a plant. It might stay firm in the ground, but it will never sprout. Learning to identify the eye is the most important part of the splitting process. For more on tuber structure, see Dahlia Tubers: What You Need to Know.
When Is the Best Time to Split?
There are two schools of thought on when to split dahlia tubers: in the fall right after lifting them, or in the spring before planting. Both methods work, and the "best" time often depends on your schedule and storage conditions.
The Case for Fall Splitting
Many gardeners prefer to split their dahlias in the fall, shortly after digging them up. At this stage, the tubers are soft and much easier to cut. Once they have dried out for a few weeks or months, they can become quite tough and leathery. Fall splitting also saves a significant amount of storage space. Instead of storing large, soil-heavy clumps, you are only storing clean, individual tubers.
The Case for Spring Splitting
The main challenge with fall splitting is that the eyes can be very hard to see. They are often dormant and look like tiny pinpricks. In the spring, as temperatures warm up, the eyes begin to swell and may even start to sprout. This makes it much easier for a beginner to see exactly where to cut. If you are unsure about identifying the eyes, we recommend waiting until spring or "pre-sprouting" the clumps in a warm room for a week before splitting them. If you are not sure how your climate compares, check the Hardiness Zone Map.
Curing the Tubers
Regardless of when you split, the tubers need a short period to "cure." If you split them in the fall, let the cut ends dry and callus over for 24 to 48 hours before packing them away for the winter. This creates a protective barrier that helps prevent rot, and if you are placing a new order for spring, review our shipping information.
What to do next:
- Decide if you have the storage space for whole clumps or if you need to split now.
- If you can't see the eyes, wait a few days after lifting; sometimes they become more visible as the skin dries slightly.
- If you choose to wait until spring, ensure your storage area stays between 40°F and 50°F to prevent early sprouting.
Tools and Sanitation: The Golden Rule
Before you begin the physical work of splitting, you must address the most important rule of dahlia care: sanitation. Dahlias can be susceptible to viruses and bacterial diseases, such as crown gall or leafy gall. These diseases can be spread from one plant to another through your cutting tools.
For a broader overview of dahlia care, see All About Dahlias.
Selecting Your Tools
You don't need fancy equipment to split dahlias, but your tools should be sharp.
- Garden Snips or Pruners: Good for cutting the main stem and smaller tubers.
- A Sharp Knife: A paring knife or a linoleum knife can help you make precise cuts in tight spaces.
- Loppers: Useful for very large, woody clumps that are too thick for hand snips.
The Disinfection Routine
You must disinfect your tools between every single clump. If you skip this step, you risk infecting your entire collection with a disease that might have been present in just one plant. Longfield Gardens stands behind our plants with a 100% Quality Guarantee.
We recommend using a solution of 70% isopropyl alcohol or a 10% bleach solution (one part bleach to nine parts water). Simply dip your tools into the solution for about 30 seconds after you finish one clump and before you start the next. Some gardeners keep two sets of snips in a jar of alcohol, rotating them so one is always being sanitized while the other is in use.
A Step-by-Step Guide to Splitting Dahlias
Once you have your tools ready and your tubers lifted, you can begin the process of division. Follow these steps for the best results.
Step 1: Clean the Clump
It is much easier to see the eyes and the structure of the clump if you remove the soil. You can use a gentle stream of water from a garden hose to wash the tubers. If your soil is heavy clay, you may need to use a soft brush or a screwdriver to gently poke out the dirt from the center of the clump. Be careful not to nick the skin or snap the necks during this process.
Step 2: Remove the "Mother" Tuber
The "mother" tuber is the original tuber you planted in the spring. You can usually identify it because it looks darker, more wrinkled, and "older" than the fresh, new tubers that grew around it. In many cases, the mother tuber will begin to rot or become woody. It is usually best to cut this piece away and discard it, as it is less likely to produce a vigorous plant the following year.
Step 3: Assess the Size
When you start cutting the clump into individual pieces, look for tubers that are a healthy size. A good rule of thumb is the "battery test." We like to see tubers that are at least the size of a AAA battery.
If a tuber is very small—about the size of a jellybean—it may still grow, but it will have very little energy stored. It might produce a smaller plant with fewer flowers. Conversely, if a tuber is huge (larger than a baked potato), you can actually trim off the bottom half of the body. This encourages the plant to grow new roots rather than just sitting on its old energy reserves.
Step 4: Locate the Eyes
Look at the crown of the plant where the tuber necks meet the stem. Look for small, raised bumps or "pimples." These are the eyes. Every piece you cut must have at least one eye. If you find a section of the crown with three eyes, you can leave it as one piece or carefully split it into three separate tubers, provided each one has a body and a neck.
Step 5: Make the Cut
Using your sharp, sanitized tool, cut through the crown. You want to take a small "wedge" of the crown material along with the neck and the tuber body. Think of it like cutting a slice of pie. Ensure the cut is clean and not jagged. If you find any brown or discolored flesh inside the cut, keep trimming until you see clean, white flesh. This ensures you aren't leaving any rot behind.
Step 6: Label Immediately
Nothing is more frustrating than a box of "mystery" dahlias. As soon as you split a tuber, use a soft pencil or a permanent marker to write the variety name directly on the skin of the tuber. This is much more reliable than using tags or bags, which can get lost or separated.
Key Takeaway: Always prioritize a clean cut with a piece of the crown attached. If a tuber doesn't have an eye, it won't grow.
Dealing with Common Tuber Issues
As you work through your dahlia clumps, you will likely encounter a few tubers that don't look perfect. Knowing how to handle these common issues will help you save as many plants as possible.
Shriveled or Dehydrated Tubers
If you are splitting in the spring and find that your tubers look like wrinkled raisins, don't give up on them yet. Dahlias are remarkably resilient. Perform the "malleable test." Gently squeeze the tuber. If it feels firm or slightly flexible like a carrot, it likely still has enough moisture to grow. If it feels hollow or crumbles like a dry leaf, it is likely too far gone.
If a tuber is slightly shriveled, you can soak it in a bucket of room-temperature water for a few hours before planting to help it rehydrate.
Dealing with Rot
Rot is the most common enemy of dahlia tubers. It often appears as soft, brown, or black spots on the body or the crown. If you find rot, use a clean knife to cut it away. You must keep cutting until you reach healthy, creamy-white tissue.
If the rot has traveled all the way through the neck and into the crown, that specific tuber is likely not salvageable. However, the rest of the clump might still be perfectly fine. This is why splitting is so helpful—it allows you to remove the "bad apples" before they can infect the healthy tubers.
Broken Necks
During the lifting or splitting process, it is common for a tuber to partially snap at the neck. If the neck is completely broken, the tuber is useless. However, if it is just a small hairline crack, you can sometimes save it by wrapping the neck tightly with a bit of floral tape or electrical tape to keep it stable until planting. Generally, though, it is best to rely on tubers with strong, intact necks.
Storing Your Split Tubers
Once your tubers are split, labeled, and cured, they need a safe place to spend the winter. The goal of storage is to keep them dormant—neither freezing nor growing—and to prevent them from drying out completely.
The Right Environment
The ideal storage temperature is between 40°F and 50°F. An unheated basement, a crawl space, or a cool corner of a garage usually works well. If the temperature drops below freezing, the water inside the tubers will turn to ice and rupture the cells, causing them to turn into mush when they thaw.
Packing Materials
We recommend packing your split tubers in a medium that holds just a little bit of moisture but also allows for airflow. Popular choices include:
- Vermiculite: Excellent for maintaining a steady moisture level.
- Coarse Sand: Very stable but can be heavy.
- Pine Shavings: Often sold as animal bedding; these are clean and easy to handle.
- Peat Moss: A classic choice, though it can be dusty.
Place a layer of your chosen material in a plastic bin or a cardboard box, lay the tubers down so they aren't touching, and cover them with more material. If you use plastic bins, leave the lid slightly ajar or drill a few small holes in the sides to prevent moisture from building up and causing rot.
Mid-Winter Check-ins
It is a good idea to check your tubers once a month during the winter. If you see any signs of rot, remove the affected tubers immediately. If the tubers look very shriveled, you can lightly mist the packing material with water to add a touch of humidity.
What to do next:
- Set a recurring reminder on your calendar to check your stored tubers once a month.
- Keep a thermometer in your storage area to monitor for freezing temperatures.
- Prepare your packing materials in advance so you can move quickly once the tubers are cured.
Preparing for Spring
When the ground begins to warm in the spring, your split tubers will be ready for their new home. If you split them in the fall, you may notice that the eyes are now very prominent or even starting to grow small white sprouts. This is a sign that the tubers are healthy and ready to go.
Pre-Sprouting
Some gardeners like to "wake up" their tubers indoors about 4 to 6 weeks before the last frost. You can place the tubers in shallow trays of moist potting soil in a warm, bright spot. This gives them a head start, which can be especially helpful in northern climates with shorter growing seasons. For taller varieties, see How to Pinch and Stake Dahlias.
Planting Depth and Spacing
When you are ready to plant, find a spot with at least 6 to 8 hours of full sun and well-draining soil. Dig a hole about 4 to 6 inches deep. Lay the tuber horizontally in the hole with the eye pointing up. Space your dahlias about 18 to 24 inches apart. This gives them plenty of room to grow into those large, lush plants you enjoyed last year.
Avoid watering the tubers immediately after planting unless your soil is bone-dry. The tuber has enough stored water to get started, and too much moisture before the plant has roots can cause the tuber to rot in the ground. Wait until you see the first green shoots poking through the soil before you begin a regular watering routine.
Conclusion
Splitting dahlia tubers is one of the most practical skills a gardener can learn. It transforms a single plant into a bounty of blooms, ensures your garden stays healthy and vibrant, and simplifies the winter storage process. While the anatomy of the tuber—the body, neck, and crown—might seem complex at first, a little bit of practice will make you an expert in identifying those vital eyes.
At Longfield Gardens, we want every gardener to experience the joy of a yard filled with spectacular dahlias, and a color-coordinated dinnerplate collection can be a beautiful next step. By taking the time to divide your tubers, you are investing in the future of your garden. It is a rewarding cycle of growth that keeps your plants vigorous and your summer landscapes full of color.
- Always sanitize your tools between clumps to prevent the spread of disease.
- Ensure every divided tuber has a piece of the crown and at least one visible eye.
- Store your split tubers in a cool, frost-free place with a moisture-balancing medium.
- Label your tubers directly on the skin to keep your varieties organized.
Dividing your dahlias is like multiplying the joy of your garden. With a sharp pair of snips and a little patience, you can turn last year’s success into next year’s masterpiece.
At Longfield Gardens, we want every gardener to experience the joy of a yard filled with spectacular dahlias, and a warm-toned harvest collection is a wonderful way to build on that success.
We encourage you to try splitting at least a few of your clumps this season. Once you see how easy it is to grow your collection and how much healthier your plants become, it will likely become a favorite part of your yearly gardening rhythm, especially with a big-blooming dinnerplate mix.
FAQ
Can I plant a whole dahlia clump without splitting it?
Yes, you can plant an entire clump, but it is generally not recommended. A large clump will produce many stems, leading to overcrowding, poor airflow, and smaller flowers. Splitting the clump into individual tubers results in a more vigorous plant that focuses its energy on producing the large, beautiful blooms dahlias are known for.
What happens if a tuber breaks off without an eye?
If a tuber body breaks off without a piece of the crown or an eye attached, it will not grow. While the tuber contains energy, it lacks the "genetic blueprint" or bud necessary to sprout a new stem. These are often called "blind tubers." You can discard them or compost them, as they will simply sit in the ground without ever producing a plant.
How can I tell if an eye is viable?
A viable eye looks like a small, slightly raised bump or a tiny "pimple" on the crown of the tuber. In the spring, these eyes may turn pink or green and begin to swell, making them much easier to identify. If the eye is black, mushy, or completely dried out and brittle, it is likely not viable and will not grow.
Why are some of my dahlia tubers huge while others are tiny?
Tuber size is largely determined by the variety of the dahlia. Some types, like dinnerplate dahlias, tend to produce very large, thick tubers, while smaller border varieties or certain specialty types may produce many small, narrow tubers. As long as the tuber is at least the size of a AAA battery and has an intact neck and eye, it should grow a healthy plant regardless of its overall size.
