Dahlias
Dahlias have a way of capturing our hearts. With every shape, size and color (almost) imaginable it is every flower lover’s dream! On our last property, we always had a small patch designated to dahlias, even when we were working with less than 2,000 square feet, dahlias earned their place. Having twenty dahlias was a huge deal to us back then! Once we moved to our new property, every year we eked out just a little bit more room for the dahlias. This upcoming season we are designating enough space for 2,000. I’m often asked what my favorite flower is and much like not having a favorite child, I don’t have a favorite flower but dahlias come pretty close. By the end of this post, you will be walking away with the knowledge and tools (perhaps a little bite from the dahlia bug) to successfully grow your own.
Dahlias may not have a sweet fragrance like a rose or peony, but what they lack in fragrance, they more than make up with their magnificent beauty. With numerous varieties, it is easy to find oneself quite the hoarder of these amazing flowers. They give us a spectacular show at the end of summer and help us to greet fall. Besides, with some yummy scented geraniums as filler, who needs a scented dahlia?
Now, I will say dahlias are fairly labor intensive, especially in colder climates. Not only are you dealing with the planting, maintaining, harvesting but pulling up and dividing at the end of the year as well. Even though they can be quite demanding, when taken properly care of they have come to be one of our most reliable cut flower along with being one of the most profitable. CSA members, brides and florists all have an appreciation for dahlias. They are eye candy and I have yet to meet someone who doesn’t admire their beauty. Not to mention, there is no comparison when it comes to the beauty and quality of locally grown dahlias!
Even though dahlias pair wonderfully with our English garden aesthetic, dahlias do not originate from English gardens of European princesses. Rather dahlias come from Mexico and were believed to be cultivated and used by the Aztecs. Their tubers were used and eaten similar to potatoes- could you imagine?! Dahlias made their journey over the leaping seas a mere two centuries ago by a botanist to make a new home in Spain. From there, they have been cultivated and bred in many forms and colors (minus blue). These days they are grown more for the flower and these cultivated varieties are not recommended for eating, though my dog sure likes one as a snack once in a while.
Don't let them intimidate you. They are hardier than they look and their beauty makes them a worthy candidate in your cut flower garden! Dahlias can be grown from seed, from a tuber or a propagated cutting. From seed, they most likely won't be true to the mother plant but can make for a fun experiment and surprise at blooming time. And... what's a tuber? It looks like a scrawny yam. Kind of like growing potatoes, growing from a tuber will give you a dahlia true to the mother plant as will a cutting. Dahlias can produce anywhere from two to ten tubers from a single tuber or a cutting in one season, depending on the variety and health of the plant.
First things first, you are probably on the hunt on where to source some awesome dahlias to grow in your cut flower garden.
Should you invest in dahlia seeds, tubers or cuttings? and where to buy ‘em
Seeds
Dahlia seeds have recently become all the rage. After all, they are inexpensive and can provide a wonderful surprise. For the right person, it can even open the floodgates of a new found passion of dahlia breeding. Dahlias are quite fascinating in how dynamic they are that can lead to so many unique traits! Dahlia seeds can be easily saved from your own plants. Dahlia seeds have become quite fashionable recently, you can easily find them from Johnny Select Seeds, Floret or other small growers. And yes, plants grown from seed will produce some tubers first year. You will really want to be sure to track the ones you want to keep and cull the ones you don’t.
Starting dahlias from seed…
To start dahlia seeds we treat them similarly as we do when growing zinnias, starting them about 4 to 6 weeks before last frost. Dahlia seeds can also be direct sown after the danger of frost as passed. To get a jumpstart on the season, we like to start them in the propagation house.
To accommodate the quick growth of the seedling, we prefer growing in a 50 cell tray or two-inch soil block . Dahlia seeds like warmth for germination, ideally around 70-75F. A heat mat helps to keep soil temperatures at the optimal temperature and a humidity dome will increase speed of germination by keeping the surface soil moist (but not oversaturated). When given the ideal growing conditions, germination should occur in three to five days. A key with dahlia seedlings is not letting them get too root bound. If you cannot get the seedlings out in their growing beds timely, bump up the seedlings to larger containers to keep them happy and in turn buying yourself a couple extra weeks.
Propagated Cuttings
To keep up with the dahlia demand, many small growers and wholesalers have begun to offer cuttings, especially for the newer highly coveted varieties that have questionable tuber production and storage ability.
It is also easy to propagate cuttings from your own tubers, if you’re just looking to increase some stock last minute. From each mother tuber you can expect to get five to seven cuttings before depleting the tuber’s energy. Taking cuttings is great to do especially to increase the amount of plants you want of the more expensive or “unicorn” varieties. I would recommend taking a few cuttings but also planting the tuber and allowing it to produce flowers and tubers for you, to have your cake and eat it too!
How to propagate yourself…
Simply wake up your dahlia tubers earlier by potting them up and placing them in a warm area, an area above 55F. You can cut (with sanitized clippers) or break off a stem from the eye once they are about four inches long. Dip the cutting in a rooting hormone (our favorite is linked at the end of the post). Then place rooted cutting in a soil-less substrate (we prefer Fox Farm’s Lucky Dog or Pro-mix) in a 50-cell tray. When selecting soil-less substrate for propagating cuttings, having it with mycorrhizae is beneficial since it promotes root growth. Cover cuttings with a humidity dome lid. Keep the cutting soil moist but not soggy and mist leaves with water. With cuttings, we find ourselves misting the leaves about two or three times a day. Keep the cuttings warm, at about 65-70F but out of direct sun. A heat mat will help keep the soil temperature consistent to aide root development.
Within in about two weeks, the cuttings should begin to root. You will know they rooted when you tug on the cutting and it has resistance. Once rooted, remove the humidity dome lid.
Purchasing cuttings…
If purchasing cuttings, be sure to get cuttings from a reputable source. Dahlias can easily become infected with disease but this escalates with cuttings that come from poor stock or sanitation practices. Aside from gall, tobacco mosaic virus was another one that was spreading like fire from cuttings sold. Be aware of the symptoms, keep plants quarantined from your other healthy plants until you can determine they are disease free.
The upside is you can get some amazing varieties that there is a tuber shortage for, increase your stock last minute and the cuttings will produce tubers in first year for you!
Tubers
Tubers. Out of the three options this has been my go-to. I find quality tubers to be an easy, reliable way to get gorgeous flowers for our growing season. Since we also deal with a lot of event work, being surprised with what I am going to have blooming doesn’t work, which is a downside of growing dahlias from seed. A bride who wants blush isn’t typically going to go for yellow, get what I’m saying?
When I was looking to increase stock fast, we did purchase from our wholesaler who imported from Holland. Now there is an upside: it’s a quick and inexpensive way to increase your dahlia stock. The downside is that imports can come in the incorrect variety, get cancelled or come diseased. If you do decide to purchase tubers from a wholesaler; be sure to carefully inspect each tuber clump prior to planting, when lifting and dividing as well.
Purchasing from other small scale growers is my true preference. I like to support small scale farms when I can. There have been a handful of times where I did get either blind tubers, rot or even disease. Purchasing from small scale growers doesn’t eliminate these problems with purchasing dahlia tubers but it is less frequent and small scale growers do have more care behind their products.
With a handful of tubers, I know I can usually quickly multiply my stock. Dahliaaddict.com is one of my favorite resources but honestly, I tend to find growers I’ve come to love and stick with them since I appreciate their commitment to quality.
Big Box/ Retail Nurseries
I decided to throw Big Box/Retail nurseries in their own group. You can easily find tubers at big box stores, usually beginning in about March. You may or may not get what is actually pictured on the label. You can also find dahlia plants available at places such as Costco. These can be great option of someone who isn’t banking on having those dahlias perform as cut flowers for their business. If you are growing for sale, I recommend sticking with the options of purchasing from reputable sources that are selling varieties that are suited as cut flowers. There are tons of beautiful dahlia varieties but some are better for the landscape.
Since growing dahlias from tubers are the most common method, let’s get familiar with what a dahlia tuber is, what it looks like and how to troubleshoot them.
Inspecting your tuber
Dahlias are tougher than we give them credit for, so are their tubers. With that said, it’s important to be able to identify a viable tuber versus one that is not and one that is healthy versus diseased. Let’s go over the anatomy and for further visuals, we have some videos at the end of this post as well!
First, knowing the anatomy of a dahlia tuber helps tremendously.
There are three main parts to a dahlia tuber:
Crown
Neck
Body
The crown is the upper most part of the tuber, this is where the eye comes from, the plant. Without an eye, there will be no plant and thus no flowers.
The neck is the middle part of the dahlia that connects the eye with the body, which is the energy source of the dahlia tuber. Ideally, the neck should be intact to produce a viable plant. A broken neck may result in the the plant not having enough energy to mature and dying off.
The tuber should be firm to the touch and look plump. Slight shriveling doesn’t mean that the tuber isn’t viable but too much shriveling and it won’t be.
Watch for Disease!
Red flags of the tuber would be an eye that is sending a sprout that looks similar to cauliflower or something from a horror film where a zillion eyes are trying to shove out of one eye socket. Commonly this is leafy, crown gall or what is commonly called “dahlia gall.” Gall will result in many stems of leaves (if the plant doesn’t die first) but no flowers and often the plant dies This is caused by Rhodococcus fascians, a bacteria easily transmitted from wounds of a plant such as what cutting does. This is easily transmittable which is the bane of the dahlia world. Sanitizing tools in-between plants with a diluted bleach solution or hydrogen peroxide is recommended. If gall is suspected it is best to follow the practice “when in doubt throw it out.” This particular bacteria does naturally occur in the soil and can transmit even through water. Rotating your dahlia crop along with sanitation practices can help prevent the spread.
Having gall is different than a tuber having multiple sets of eyes on the crown. In fact, having multiple sets of separate eyes means that many more stalks that will shoot out, which is a bonus! A quick Google search should give you. a great visual to decipher between a diseased tuber versus one with happy eyes.
Planting Dahlia Tubers
When to plant
Dahlias originate from Mexico, they are heat loving plants that are frost sensitive, though I have found the hybrid varieties of today to be much tougher than zinnias. Dahlias are best grown once the soil temperatures reach minimally 60-65F.
For us, we plant tubers out in the field in late April or into May, depending on how our spring is going. There have been times when a late frost came and nipped the emerging plants but new growth shot out, though it did delay flowering some and stress the plants out more than we would prefer. Planting and placing under micro frost cloth tunnels in climates with temperature swings or late frost may help the plants to better cope.
Soil Prep, spacing and planting
We amend our dahlia patch much the same as we do our other growing beds: quality compost and slow release fertilizer. Dahlias aren’t extremely hungry plants. When planting tubers, the majority of the storage is in the tuber itself. We have soil that is lower in nitrogen, luxury amounts of phosphorous and are in an arid climate. Dahlia tubers are prone to rot, having well draining soil greatly helps combat this. Over the years, we have built up our soil with organic matter and created a friendly environment for soil beneficial worms that have enriched the soil naturally. A soil test is recommended for dahlias and in our experience, over-fertilizing can negatively impact dahlia’s health and productivity leaving it vulnerable to aphids and more leaves with less flowers. Sometimes less is more, dahlias is one of those crops where this applies.
Our main growing beds for the dahlias is our 3 1/2 feet wide by 100 feet long rows. In each bed, we plant three rows of dahlias at 15” apart. This spacing allows us to fit 240 dahlias per bed. If your soil has more nitrogen and/or you are growing in a more humid climate, giving your dahlia plants more space may be needed to increase air flow and decrease disease.
When planting dahlias, we have used the trench method, a post hole digger and a hori knife. Our current favorite method is using a drill auger, allowing us to plant quicker and more efficiently.
A majority of what we plant, especially that last few seasons, are single tubers. After some experimentation, we dig a hole about one and half to two times the depth of the size of the dahlia tuber and lay the tuber on its side (rather than up and down). We found our plants grew more durable and there was less of a chance for the dahlia neck to snap mid growing season. I orient the dahlia tuber so the body is closer to the drips, since that is where the roots will be growing from.
Watering
In our arid climate, we have found dahlias to need quite a bit of water as soon as they are planted. In fact, for more seasons than I prefer to admit, we greatly under-watered our dahlias in fear of causing them to rot. We use drip irrigation that has eight inch spacing between emitters and is low flowing to allow us to give a deep watering. We water our dahlias either every other day or every day depending on temperature and wind for an hour. Be sure to check the moisture levels of your soil and watch your plants to determine the correct watering amount. Lack of growth or shriveling may indicate too little water. Yellowing and blackening of plants may indicate too much.
Trellising
Dahlias, especially dinner-plate varieties, can get quite top heavy where between a gust of wind or a good rain can cause the plant to topple over. Sometimes the falling of the plant can even lift the tuber from the ground. Our favorite method of trellising dahlias to help prevent broken plants but still be able to easily harvest and lift the tubers in fall is the “corral” trellising method. This is where we take baling twine and rebars and wrap the twine around the growing bed. Between the plants themselves and with the help of the trellis, the dahlias are able to stay nice and standing.
growing and bug battles
Once planted, with proper irrigation dahlias become relatively fuss free. We do not fertilize our dahlias outside of the amendments added when prepping the soil.
Pinching
Dahlias will reward you from pinching and cutting hard. It may seem counterintuitive but be assured it will greatly reward you with plenty of long, usable stems. Once the dahlia plant reaches about twelve inches and has four sets of true leaves. On the stalk of the plant, pinch down to the next set of leaves. This removes the terminal bud and encourages the plant to redirect energy to branch. Pinching may delay the plant some but not as much as allowing the terminal bud to bloom, where you will need to cut hard to encourage branching which may take more time and plus, you’ll have a stem like a broom handle!
A big battle with growing dahlias are the buggers who are also fans of dahlias…
Battling Thrips
Thrips are one of those annoying foes that show up fairly early in the season. Once they've moved on from the sweet peas and ranunculus they move over for the dahlias. Fortunately, a few years ago some tiny little lady birds showed up in our field. After a week of battling them we brought out the macro lens and decided to really figure out what these little guys were. There were tons of them but they didn’t seem to be hurting our crops. In fact, once they showed up we found the population of thrips went significantly down. Each June these little fellas show up to get the thrips under control moving from sunflowers to the dahlias, which has left the amount of thrips population in our dahlia patch quite negligible.
Battling Earwigs
Our biggest battle are the buggers who are also fans of dahlias. Earwigs and leafhoppers are our biggest battle. Typically earwigs are more problematic earlier in the season, as they love to nibble on the tender growth of the plants. We have found the best solution is to use earwig traps. In either recycled cans or other shallow containers/cups/dishes we fill the traps with equal parts cheap cooking oil, soy sauce and Kara syrup (though beer works too). We then take the containers and bury them where we find the most damage so the container sits flush to the ground. The smell of sweet and fermentation attracts the earwigs, they swarm in and drown.
Battling Leafhoppers
Leafhoppers are not quite as easy to prevent as the earwigs. We find using knockdown sprays, keeping weeds at bay, encouraging beneficial predatory insects and keeping the plants stress free to be the most helpful in combatting leafhoppers. Leafhoppers can quickly get out of control and stress out the dahlias causing discoloration which leaves them more prone to powdery mildew along with other diseases. Beneficial nematodes, parasitic wasps, assassin bugs, brown lacewings, damsel bugs, green lacewings, lady beetles, minute pirate bugs, and spiders are some natural predators of leaf hoppers.
Other Mentionable Pests, Disease Battles (and what to do about them)
There aren’t too many pesky pests who don’t love dahlias. Other foes you may be faced with depending on your growing area are: slugs, snails, aphids, Japanese beetles are some other common pests who can decimate a crop. Traps, biologics and OMRI certified pesticides such as pyganic and Sluggo Plus may help with all the above pests and never underestimate the power of knowing them into a bucket of soapy water! Research your chosen method carefully, the best is using the various tools available as your “integrated pest management system.” When using sprays, be sure to read directions on the bottle and spray at dusk once the beneficials are no longer active for the day to avoid hurting them.
Dahlias are not only susceptible to gall, tobacco mosaic virus but is also prone to downy mildew, wilt and more. Preventative measures can help such as spraying a fungicide, especially after a rain storm. To see more information on the various diseases and pests that dahlias can fall victim to check out this website.
Harvesting Dahlias
Days to Maturity
Typically from planting dahlias take about 90 days, give or take depending on the variety. There are varieties that bloom earlier in the season, mid season or late season. For example, Arabian Night and Wizard of Oz are two of our earliest bloomers, coming in usually by Mid-July from a Late-April to Early May planting. A majority of our ball varieties and informal decorative such as Cornel and Silver Years come into bloom in late July/early August. As with many things, the best of the show comes in later. Our dinner plates such as Cafe Au Lait, Shiloh Noelle and Rip City come in strong late August through first frost.
Note the papery back petals of these Breakout Dahlias, much past their prime to be used as a cut flower but still beautiful for a quick photo!
Harvesting
Harvesting is best done in the cool of the day, preferably in the the morning. Harvest when the flowers are three quarters of the way open, before the back petals become papery and old. Dahlias can be cut slightly less open and will eventually open, though they are slower to open.
A rule of thumb for harvesting is to cut the stem the length of your forearm and cut to the next base with basal leaves to encourage new growth. Place stems into a sanitized bucket of water with a CVBN tablet. From there, place in cooler or a dark, cold location to hydrate preferably over night but a minimum of a few hours. We typically rubber-band ours into five stem bunches.
Some growers have found dahlias to have an extended vase life by searing the stems in in boiling water and allowing the stems to cool for an hour, we personally have found no difference in vase life using this method versus simply cutting into a cool bucket of water. Experiment and take notes!
Vase Life
Ball, pom and decorative varieties have the better vase life of about five days. Dinner-plate varieties are best used as an event flower or to delight in for one to three days. Dahlias benefit from the use of flower food.
Using Dahlias in Designs
Dahlias steal the show! They are our most requested flower, even surpassing peonies. Dahlias are a luxury flower and we use them as such: the star focal flower. Especially as a wedding farmer-florist each form of dahlia has its purpose in design. Dinnerplates are gorgeous for larger designs such as arbors but can be equally beautiful in a bridal bouquet. The pom varieties may not seem like much compared to many of the other forms but when it comes time for boutonnieres or corsages, they are adorable buttons that hold up well. The ball varieties are the absolute best for those “kitchen table” type products and have a longer vase life. Dahlias can be great for the scooped from the garden look or incredibly sophisticated for a more formal wedding!
Fall Clean Up
In our area, the winter is too cold to safely overwinter the tubers in the ground. Dahlias are hardy down to hardiness zone 8 (we are 6b, even with the new hardiness map being released… we still feel we are zone 6b). Though, there are many tricks to be able to overwinter them in colder zones and we have even done so successfully, we find it too risky.
In the fall, the tubers are dug up and stored for planting the next spring. If that seems like too much effort, mulching the dahlias heavily may protect them enough to overwinter. Either way has risks. Digging up and storing can result in some tuber rot, if not stored correctly or some just rot in general and no fault of our own. Storing properly will help. Be on the look out for our blog post on which tuber storage method works for our arid climate.
To learn more about lifting, watch the video below!
Multiplying your dahlia stock
As mentioned earlier in this post, you can propagate more dahlias from cuttings or seeds saved. The most common way to multiply stock is through dividing your dahlia clumps. To learn more about dividing and storing dahlia tubers, watch the two videos linked below!
I can keep rambling about these summer favorites. At some point: I should cut myself off and save some ramblings for another post! Whether you are a dahlia enthusiast, a farmer, florist or home gardener I hope you enjoyed learning a little about what it takes to grow these amazing blooms (and are now inspired to grow some in your own cut flower garden!).
We are looking forward to helping you hand blooms soon!
Jessica & Graham
Products and Resources we find useful with dahlias!
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For propagating cuttings we like to use this rooting hormone:
Clippers and knives for harvesting and dividing:
Additional books to feed your dahlia obsession: