Dahlia Care Guide
Our first plot of dahlias!
Planting
Check your plant hardiness zone or enter your zip code into the Farmers Almanac to determine your average last frost date. This date will tell you approximately when it is safe to plant your dahlias outside.
After the last chance of frost has passed, dig a hole or trench about 4-6” deep and as wide as your tuber.
Plant your tubers horizontally at 12” spacing.
If there is a visible/sprouting eye, place it in the soil facing up towards you.
Don’t worry if the tuber hasn’t sprouted yet. The sprout will find its way to the top of the soil, regardless of which direction it is planted in.
Completely cover the tubers with soil, and add a layer of aged compost on top for additional nutrients to be released throughout the season.
DO NOT WATER THE TUBERS. Watering before the tubers have sprouted above the ground can cause them to rot. Wait until the majority of your tubers have sprouted before giving them a drink.
Growing & Harvesting
When the sprouts are about 12” tall, remove the top couple inches of growth just above a set of leaves to pinch the plant (see Figures 1 and 2). This encourages the dahlia to branch out and produce more stems and flowers.
Most dahlia varieties can reach 3-6’ tall, and they benefit from having support in place.
We corral our dahlias by stringing baling twine between our t-posts (spaced at 20 feet apart) to create a horizontal fence. The twine is wrapped tightly around each set of posts. The first layer of twine is positioned about 2 feet off the ground, and we create a second layer at the 4 foot mark.
We remove the twine at the end of the year and reuse what we can.
To harvest, cut deep into the plant - at least 18-24” (I use the length of my arm for consistency and ease of measuring). This will act as a continual pinching process, encouraging the plant to keep producing more branching stems. It’s okay to sacrifice buds that are forming for the sake of getting a longer stem. There will be two new stems in that bud’s place.
Dahlias should be harvested when they are fully open or close to it. They will not continue to open in the vase once they are cut.
Check the back of the flower head to see if the petals have curled backwards, are wilting, or are turning brown. These signs indicate that the flower is old, and it won’t last long in the vase. Harvest before this stage to ensure the longest vase life possible.
Harvest the stems directly into water. We recommend cutting them early in the morning or in the evening after the heat of the day has passed. This is when the stems are the most turgid and retain the most water.
Figure 1: Where to pinch the dahlia stem.
Figure 2: What the stem should look like after pinching.
Digging & Storing
Dahlias are not cold hardy and will need to be removed from the ground if you live in a zone that doesn’t stay warm year round. There are several storage methods to choose from, and the success rates can vary from year to year. We encourage you to try experimenting with different methods to find the one that works best for you. Our preferred process is outlined below.
Before the first frost happens, go through each one of your dahlias and do two things:
Make sure each plant is the correct variety to what it has been labeled as.
Flag or pull out any plants that are diseased. Diseased plants should be landfilled or burned, not composted. Some signs of disease include:
a significantly shorter plant or significantly fewer blooms than what is average for the variety (given proper growing conditions)
mottling or deformity of the leaves (potentially Dahlia Mosaic Virus)
powdery mildew. This can be treated for during the growing season, and isn’t necessarily a reason to dispose of the tubers. However, some varieties are more susceptible to it than others. To protect your stock, you may not want to keep tubers from infected plants.
Learning to spot signs of disease can take time, practice, and dedicated research. For new growers and beginners, try starting with learning the behaviors of your plants, then take notice of anything that stands out of the norm.
At the end of the season, cut your dahlias down, leaving about 6” of the stalk above the ground.
The first frost will kill the green growth and flowers on your dahlias. You can wait until after this occurs to begin the cutting process. Alternatively, you can use the cutting process to act like a frost if you want/need to pull your tubers out before then.
Cutting the stalks down also encourages eyes to form on the tubers, which makes it easier to divide them.
Leave the tubers in the ground for at least two weeks to harden them off in a process calling curing. The tubers are safe to be left in the ground until the ground begins to freeze.
After waiting at least two weeks, you can begin digging the dahlias out of the ground.
Position a pitchfork about a foot away from the main stalk and carefully start digging the tubers out.
Work your way around the tuber clump, loosening the soil one side at a time.
When the soil is sufficiently loosened, position the pitchfork under the clump and guide it out of its spot. You can use the remaining stalk as a handle to help stabilize the clump, but we don’t recommend using it solely to pull the clump out. If the stalk breaks, it can make transporting and dividing it more difficult.
Gently remove excess clumps of soil.
We tried three options this year for how much soil we left on our tuber clumps:
The first group was left completely encased in soil, and they stored really well.
Our second group had very little soil surrounding them, and they turned out even better.
The third group that had a moderate level of soil only stored okay.
Storage success is dependent on a number of factors (like humidity, the tuber variety, temperature, storage container and medium, etc), and it can change every year.
We recommend trying different techniques to see which option will work best for you. We will be removing the majority of the soil from the clumps next year to save on space and make dividing in the winter/early spring easier.
Bring the tubers into a covered area like a garage or shed, and allow them to dry and cure for 2-7 days before placing them in storage.
Make sure that the tubers are not resting directly on concrete, as this will encourage the tubers to dry out. Placing a tarp down first or using crates/bins to contain the tubers can be helpful.
Place the tubers in a crate, plastic storage container, or paper bag with a label of what the variety is. We had great success this year with storing them in bulb crates without a packing medium.
Peat moss/coco coir, vermiculite, or sawdust/wood shavings can be used as a packing medium, but might not be needed, depending on your storage conditions.
Three Acre Farm recommends keeping the humidity in your storage area around 70% to prevent the tubers from drying out, but not being so humid that they rot. Using a combination of the storage containers and packing mediums can help to adjust for the humidity. In some cases, you might want to use a humidifier or a dehumidifier if you notice your tubers shriveling or rotting, respectively.
Tubers need to be stored between 40-50° F.
Frozen tubers may not survive, while tubers stored at higher temperatures might rot.
We used a small $20 personal fan heater plugged into a cheap, programmable outlet plug in our cooler to keep our tubers warm through the winter. Friends of ours use their heated garage, while others store in crawlspaces and basements. The options are plentiful!
Check on your tubers every couple of weeks to ensure that they aren’t drying out, molding, or rotting.
Remove and discard any tubers that are mushy and rotting.
Tubers that are molding, but have not yet rotted, can be cleaned off and placed separately back into storage. Mold usually starts to occur when the humidity is too high. Let those tubers completely dry after cleaning them, then try placing them in a paper bag with some vermiculite to adjust the storage conditions.
Tubers that are drying out should be placed into a storage option with higher humidity. This can be achieved by filling a plastic container with peat moss/coco coir that gets spritzed with water here and there.
As spring approaches, you can begin waking your tubers up by placing them in a warm room. They don’t need sunlight until the sprouts start to develop. Once you have sprouts, you can pot the tubers up to get a jump on the season, or you can wait to plant them outdoors after the first frost.
Additional Resources:
Dividing
You can divide your tubers right after you pull them out of the ground in the fall, or you can wait until the winter or early spring.
To divide in the fall, add these steps to the Digging and Storage section above:
After digging the tubers up, manually remove as much soil as possible. Don’t shake or beat the clumps on the ground, since their necks are fragile and vital to having a usable tuber.
Use a hose to wash the remaining soil and debris off the tuber clumps.
Collect your snips, a sanitizing solution like Clorox or a 10% bleach/water mix (for sanitizing the snips with between each clump), and designate an area or tray to let the tubers completely dry in before storage.
First, sanitize your snips. Then, use them to remove any roots and broken tubers from the clump (see Figures 1-2). If you accidentally pierced a tuber with the pitchfork, remove this one too.
Figure 1: What a clump of tubers might look like before dividing.
Figure 2: What the clump looks like after removing the roots and broken tubers.
5. Cut the stalk off the clump, leaving about 1-2”. Cutting the stalk too far down may jeopordize the eyes.
6. Cut the clump in half, preserving as many tubers with eyes as possible (see Figures 3-5). It’s normal to sacrifice some tubers in this process.
Dividing the clump in half or into quarters makes it more manageable and easier to further divide into single tubers.
Figure 3: Anatomy of a tuber. Make sure the neck and body are intact, and identify the eyes.
Figure 4: The eyes of a tuber may look like nodules or might be sprouting. If you’re unsure of where the eye is, leave as much surface area on the neck as possible when dividing, or wake your tubers up to enccourage the eyes to grow.
Figure 5: Sprouting eyes on a dahlia tuber.
7. Identify the eyes on each tuber in the clump, and divide the clump into individual tubers (see Figures 6-7).
Figure 6: Identify where the eyes are and form a plan of where to divide the clump and trim the ends. Trimming the ends is not always necessary, but can be helpful to untangle the clump.
Figure 7: The divided tuber clump.
8. Allow the tubers to dry in a covered area like a garage or shed. The cuts made from the dividing process should form a film/scab before being
placed into storage.
Depending on the temperature and humidity of the room, this might take a couple of days to a week.
Be cautious though to not let the tubers dry out, as they will start to shrivel and become unusable if they go too far.
9. Sanitize your snips in between each new clump of tubers and repeat this process for your remaining tubers.
10. Use the storage method of your choice.
To divide in the winter or early spring, follow these steps:
After digging up the tubers, remove the majority of the soil surrounding the clump.
Do NOT wash them at this stage.
Bring the tubers into a covered area like a garage or a shed, and allow them to dry and cure for 2-7 days.
Place them in bulb crates, plastic containers, or paper bags (with or without the packing medium of your choice), and put them into storage until you are ready to divide.
When you are ready to divide, you have the option to wash the tubers or to leave them as is.
We found that not washing them decreased the chances of them rotting, but it can make identifying the eyes more challenging on some tubers. We recommend experimenting with this to find your personal preference.
Sanitize your snips.
Trim off any roots and broken or rotting tubers.
Cut off the stalk. Be careful not to cut it too low, or else the eyes may be in jeopardy.
Cut the clump in half. Dividing it again into quarters might be necessary as well.
Identify where the eyes are and cut the clump into individual tubers, making sure each one has an intact neck and at least one eye.
“Waking up” your dahlias before starting this process may help with identifying where the eyes are. You can wake your dahlias up by increasing the temperature in the storage room to 60-70° F, or by bringing them inside for about 1-2 weeks. They do not require light for this process.
Allow your tubers to completely dry (including the fresh cuts - they need to form a film/scab before being planted or put back into storage). However, be cautious not to let them dry out and become shriveled.
Pot your tubers up or put them back into storage until you are ready to plant them.
If you choose to wake your dahlias up before dividing them, you may not want to put them back into storage. Your tubers will have started the growing process and may have begun sprouting. This is not a reversable process, and the sprouts may die back or break off if put back into storage.
Taking Cuttings
Taking cuttings from your dahlia tubers is an easy, quick, and inexpensive way to increase your stock. Cuttings will flower and develop tubers in the first year.
Collect supplies (see Figure 1)
Rooting hormone (see Figure 2)
I like Garden Safe’s TakeRoot powder hormone. It can be purchased on Amazon. This was a recommended product that Muddy Acres uses. Floret seems to prefer using gel. I found that the powder produces more roots faster than the gel, and it didn’t have the intense smell of the gel, which was a plus.
X-Acto knife and/or garden snips
Plant labels and a garden marker
Sharpies work okay, but can fade. Garden Markers can purchased on Amazon.
I am a visual learner, so I found that having a visual guide present was helpful when I tried taking cuttings for the first time.
Figure 1: Supplies - rooting hormone, x-acto knife and/or snips, labels, and a marker. A printed visual guide may also be helpful.
Figure 2: Two rooting hormone options - powder and gel. I liked the powder more. It produced roots faster and didn’t have a strong smell like the gel did.
2. Fill a 72 cell tray or 4 cell containers with potting mix. (Figure 3)
Place a watering tray underneath the cell trays/containers.
3. Poke holes in the middle of each cell, making sure to go all the way to the bottom of the cell. This is where the cuttings will be placed. (Figure 3)
4. Select sprouts that are between 3-6” tall. (Figure 4)
Sprouts that are shorter than 3” tend to be underdeveloped and often do not have their second set of true leaves yet.
Sprouts that are much taller than 6” tend to suffer problems with shock. Keep an eye on their growth to catch them at the ideal stage.
5. Align your X-Acto knife or snips with the base of the stem. Keeping the blade(s) parallel to the side of the tuber, slice off the sprout. (Figure 5)
If using a knife, use a sawing/slicing motion with light-medium pressure. Try not to gouge out the eye of the tuber. It can’t produce more sprouts from that site if it doesn’t have an eye. Don’t worry though - the cutting process encourages the tuber to send up additional sprouts from other eyes, so there will likely be other opportunities for sprouts.
Try to create as clean of a cut as possible - this will help it to produce roots easier. (Figure 6)
Figure 3: Fill soil trays with soil and create holes for the cuttings to sit in.
Figure 4: Sprouts between 3-6” seem to do the best. Any shorter is too underdeveloped, while much taller has trouble with shock.
Figure 5: Use a slicing/sawing motion against the side of the tuber to remove the sprout. Keep the blade parallel with the tuber to prevent gouging the eye out.
Figure 6: Try to prevent jagged cuts or missing chunks of the sprout. A clean cut will root more successfully.
6. Use your snips or your fingers to pinch out the central leader above the first or second set of true leaves. (Figure 7)
7. Remove the lower leaves from the stem. (Figure 7)
Figure 8 shows what the cutting should look like after the previous two steps have been completed.
8. Dip the last inch or so of the stem end into the rooting hormone of your choice. (Figure 9)
I tested a theory that cuttings dipped in water first, followed by the powder rooting hormone might produce better results than just the rooting hormone by itself. I found this not to be true; they both produced similar results. I would recommend skipping the water and just dipping it in the rooting hormone.
Tap off any excess hormone. (Figure 10)
Figure 7: Pinch out the central leader at the top of the sprout. Remove any lower leaves.
Figure 8: What the sprout will look like following being pinched and having the lower leaves removed.
Figure 9: Dip the stem end into the rooting hormone. A following experiment showed that dipping the stem into water before the powder hormone did not produce better results, so we recommend skipping it.
Figure 10: Tap off the excess rooting hormone.
9. Place the cutting into the cell tray and seat it all the way to the bottom. This will help the cutting wick up moisture from the watering tray below. (Figure 11)
10. Firm the soil around the cutting, add the label, and pour ~2” of water into the bottom watering tray. (Figures 12-14)
Repeat the process for the remainder of your dahlias.
Place the cuttings under lights for 14-16 hours a day.
Figure 11: Seat the stem end in the bottom of the tray. This will help it wick water up.
Figure 12: Firm the soil around the base of the cutting.
Figure 13: Label the variety. Not shown: sanitize the blade/snips between plants to prevent spreading diseases.
Figure 14: Fill the base of the tray with ~2” of water, place your cuttings under lights, and watch them grow!
Additional resources:
Muddy Acres has an Instagram Story highlight that I referenced when I started learning about dahlia cuttings. I found it to be very helpful.
The dahlia cutting section in Floret’s Discovering Dahlias book has great photos and helpful directions.
