Restoring Eden’s Dahlia Growing Guide
Dahlias are the most rewarding plants to grow, but if you want to get the most out of them, there are a few things you'll want to consider before dropping your tubers in the ground. What kind of light will they be getting? Does the soil need anything? What happens if they get over 5 or 6 feet tall? How do I get 3 times more blooms?
If you have questions, we have answers. Restoring Eden's starter guide to Dahlias will teach you how to get the most out of the Dahlias you grow.
How I Got Started with Dahlias
I first grew dahlias in my backyard in 2016. That spring, I bought five Dahlia bulbs at Home Depot and planted them next to my little rental house, having no clue what I was doing. Later that summer, I had an unruly and monstrous 10' tall Kelvin Floodlight Dahlia that was climbing up the side of the house, and I was amazed and in awe of these incredible flowers. (Spoiler Alert: Dahlias shouldn’t be getting to 10 feet tall.
Fast-forward five years, I dove head first into the world of dahlias and established Restoring Eden, planting over 200 dahlia tubers. The following year, 2022, I planted 800!
You likely landed here because you ordered from us, you're interested in growing dahlias, or you planted a couple of last years and got "bit" by the dahlia bug. All are welcome to the club. Dahlias are hardy and easy to work with, but if you understand how dahlias work, you're more likely to succeed. And I want you to experience the very best these flowers offer.
What are Dahlias?
Native to Mexico, dahlias are an incredibly showy perennial with a tuberous root system that can bear huge flowers above ground and grow even more tubers underground. Dahlias come in nearly every color. In my garden, they are planted in color order: lavender, pink, blush, white, yellow, peach, orange, coral, raspberry, red, and maroon, with most colors available in bicolor and variegated forms too.
Dahlias also have some of the best garden longevity around. A dahlia clump planted one year might produce blooms for you more than 30 years later!
Dahlias Forms
According to the American Dahlia Society (ADS), there are 26 forms of dahlias, including formal decorative, informal decorative, cactus, ball, collerate, anemone, and a host of others. Dahlias are ideal for growing in the garden and are often used in floral event work and cutting bouquets, despite their typical 5-7 day vase life.
And the best part is estimates say that there are around 50,000 classified dahlias worldwide, with many more waiting to be discovered. Every year, Dahlia breeders and home gardeners worldwide unveil brand-new varieties. The complexity of the dahlia's DNA makes cultivating new varieties a joy that every grower can experience.
Dahlias Sizes
In addition to forms, Dahlias are also classified by size ranging from dinnerplate (AA) size dahlias that can get in access of 12” in diameter and bloom as small as your thumbnail. While Dahlia have a tremendous range of sizes, they can be divided into six general categories:
AA (Giant or Dinnerplate): These dahlias are typically over 10" in diameter
A (Large): 8-10"
B (Medium): 6-8"
BB (Small) 4-6"
M (Miniature) up to 4"
BA (Ball) up to 3.5"
P (Pompon) up to 2"
Tubers vs. Seeds vs. Cuttings
Dahlias can grow from tubers, seeds, and cuttings. Most gardeners plant dahlias from tubers, which people often confuse with "bulbs." Dahlia cuttings and seeds are also viable, but they require a bit more care and can be challenging for new growers.
Over a growing season, dahlia plants will produce tuber clumps underground at the base of the main stem. Some Dahlia growers spend hours every fall digging up these tubers and collecting anywhere from 3 to sometimes over 20, carbon copies of the same dahlia they enjoyed all season long.
Growing Dahlias from Seed
Seed Dahlias can be a great way to get started. You will be amazed at how many seeds Dahlia growers worldwide produce every year. Growing Dahlias from seed is incredibly satisfying for experienced Dahlia growers. Restoring Eden now has some dahlia seedlings that are now going into their 4th season.
Dahlia seeds get their genetic makeup from the Dahlia parents from whom they came. Dahlias are not naturally true to seed because of their complex DNA structure—another conversation for another day. What it means for the grower is that if you collect 20 seeds from a single flower, those seeds will grow into 20 completely different flowers with varying characteristics as their Dahlia parents.
Growing Dahlias from seed is a craft, not a science. Dahlia seeds do not come true to type, and Dahlia breeders with years of experience are constantly working to discover the next brilliant variety.
Where To Buy Dahlia Tubers
Dahlias can be purchased from small Dahlia growers, seed companies at Dahlia shows, online Dahlia retailers, and even some big box stores. But, all dahlias are not created equal. Check out this article to learn more about what to expect if you purchase from a big-box retailer or importer.
Tubers or cuttings can be ordered from Dahlia breeders or growers on their websites, pre-ordering as early as October and up until May of the following year.
Restoring Eden's dahlia tuber sale usually takes place in December.
Where To Plant Your Dahlias: Spacing and Sunlight
Where you decide to plant your dahlias boils down to spacing and sunlight. Dahlias spacing is vital as tubers should be spaced at least 18 inches apart, with 12 inches in-between, if planted in rows. If in a garden bed, just be sure that you don't crowd them or that they don't get overrun by other plants that might outpace them in the early growing stages.
Dahlia tubers need 6-8 hours of sunlight per day, so they should be spaced out evenly to ensure they receive that amount of sunlight.
Solutions for Space Issues
If you struggle to figure out where to plant, grow bags have become a more viable solution for some growers. Those dealing with space limitations, renting property, or challenging soil issues; have found a friend in grow bags.
Grow bags are available in our store. 5-gallon grow bags are sufficient for most varieties, and 7-gallon grow bags are for AA-size tubers or large tuber producers. In different seasons, we have also used grow bags to grow dahlias.
The Importance of Soil
Dahlias prefer loose, well-drained soil. Dahlias do not like “wet feet,” so ensure the area you plant them in drains well after heavy rains, or you may put them at risk of rotting. Add a few inches of compost to enrich the soil before planting Dahlias.
Dahlias also prefer slightly acidic soil, so if you have alkaline soil, consider adding organic compost tea to lower the pH. If you live in an area with poor soil conditions, don't be alarmed. Dahlias may be one of the few things that grow well for you, and there are always grow bags to give optimal soil conditions. Either way, it is a matter of science and experimentation to get the soil to optimum health in your growing area.
The late fall or early spring months preceding your tubers going in-ground are great times to check the health of your soil. One way to know exactly what's going on is to get a soil testing kit. Soil testing kits, will tell you if your soil lacks key nutrients that help flowers grow at their best. They might also make specific suggestions for what your soil needs.
What Month Do You Plant Dahlias?
Your local hardiness zone is what determines when you plant Dahlia tubers. They should always be planted after your zones last frost. Click here to the find the zone for your part of the country. While Dahlias need a cooling period during winter, they cannot handle hard frosts and freezes. Typically that means you'll be planting your tubers outdoors from early May to early June.
The second thing you'll want to look into before planting Dahlias is the length of the day and the amount of sunlight your plants will get. Remember that Dahlias require at least six hours of daily sun for optimal growth.
How Deep to Plant Dahlias
Dahlia tubers should be planted in at least 4-6 inches of soil, depending on the size of your bloom. Dahlias grow from a tuberous root, which means they'll need to be planted in loose soil so that the roots can easily spread throughout the soil and take in nutrients. Place your dahlia tuber on its side with the eye of the dahlia tuber facing up. Cover it up with soil and wait. BE PATIENT. Some dahlias can take up to 4 weeks before they begin to break the surface.
Watering & Care of Dahlias
Be mindful of when and how you water Dahlias. Dahlias require a consistent water supply in the soil, so avoid frequent watering, which can promote shallow root systems. This can be the trickiest thing to figure out, but once you've got your wings, you'll be able to care for dahlias and help them flourish.
Don’t start watering straight away. Young dahlia plants do not need a lot of water; in fact, excessive water can lead to the rotting of the plant before it even breaks ground. So wait until you see a few inches of growth and their first set of true leaves before you begin with regular watering.
A good rule of thumb for larger plants is to water if the rainfall is less than one inch in seven days. Dahlias in grow bags or pots will require more regular watering.
Optimal Growth for Dahlias: Pinching & Deadheading
Do you want about 3-4 times as many blooms from the same plant? Then you must pinch your dahlias. Pinching removes the main growing tip you'll see when flowers start growing. Doing this will encourage new growth and create branching, leading to blooms.
For dahlias specifically, pinch for the first time once when the plants are about 12-14 inches tall. For (AA) large-size dahlias, you typically leave 2-3 sets of leaves, while you might leave 4-5 sets of leaves for a (BB) small-sized flower. For more information on pinching, read our article, "How to pinch Dahlias for a healthier plant and more flowers" (link: https://www.restoringedenflowers.com/growingtips/pinching-dahlias)
Deadheading Dahlia blooms or clipping off spent flowers will also produce more blooms from your Dahlias if done regularly throughout their season. The more Dahlias bloom, the more energy they store in their tubers for next year's show which is why it is important not to let dahlias go to seed.
Supporting Dahlias
With some varieties having enormous blooms and some dahlia plants standing over 6' tall, they can quickly become top-heavy and need to be staked. Staking dahlias will help keep them upright and away from other plants. If staking individually with rebar or bamboo, stake the plant when you put the tuber in the ground. That way you avoid stabbing it later on. Other methods for staking include tomato cages and the corral method, a technique used to keep rows of dahlias supported using T-posts and hortanova netting or bailing twine.
Weed Control
Keeping Dahlias weed-free will prevent the spread of illness. Dahlias are susceptible to viral diseases which can be passed on through weeds. Don't make your dahlias compete for nutrients with weeds, putting down a layer of mulch around the plants can not only help to prevent weeds but will help the plant retain water, thus requiring even more.
Diseases & Pests that Dahlias Face
Dahlias are susceptible to several diseases and pests that can affect their growth. Dahlias can be affected by the Dahlia mosaic virus, Dahlia leaf spot, leafy or crown gall, spider mites, grasshoppers, aphids, and more.
Powdery Mildew
Dahlias are also susceptible to powdery mildew which appears as a white to gray powder on Dahlia leaves. This fungus can cause Dahlia buds and blooms to drop and for the foliage to die.
Affected Dahlias will grow generally during the day, but their growth will slow or stop completely when temperatures cool in the evening. The best solution for this is prevention: avoid overhead watering and prune dahlias weekly to help promote airflow and decrease humidity around them.
You can treat powdery mildew by spraying it with a fungicide containing chlorothalonil every 7-10 days until it disappears. If you're going with an organic approach, try neem oil. Neem oil is a natural fungicide that will protect your dahlias from powdery mildew.
Fertilizing Dahlias
Dahlia Tubers contain all the nutrients your plant will need when planting. The best you can offer them is well-composted manure and rich soil to begin their journey. Three to four weeks after your Dahlias go in the ground, they will generally benefit from regular treatments with a water-soluble or granular fertilizer every two or so weeks.
Traditionally, dahlias can begin with a high nitrogen fertilizer through the middle of the season but minimize nitrogen at the end of the growing season. Too much nitrogen can lead to small blooms, underdeveloped tubers, and even rot. Again, if you had your soil tested, you would be more equipped to give them exactly what they need.
How Long Do Dahlias Bloom?
Once in the ground, it can take dahlias anywhere from 75-120 days to bloom, depending on the variety. For most growing zones in the U.S., you will typically see your dahlias start to bloom in July or August. Your dahlias will continue to bloom until your first hard-killing frost.
Dahlias for Cut Flowers, Arrangements, Weddings, and Bouquets
Dahlias are highly sought after for bouquets, events, and arrangements. Dahlias are some of the most beautiful flowers that you can use to create something ornamental and special, for yourself or as a gift.
Dahlia flowers will last up to one week if harvested at the correct time, fed properly, and kept in water. The typical vase life is five days, which makes them great event floral. Dahlias are also great for cut flowers because they don't have thorns like roses do, and Dahlias come in all shapes and sizes.
Dahlias are also grown for competition, explicitly known as show Dahlias. Dahlias are a tremendously beautiful cut flower, but the show variants are generally bred for their incredible size and flawless foliage and form.
When to Harvest your Dahlias
Dahlias must be cut before the flowers reach full maturity. If harvested too soon, they will lack the size and beauty you're looking for, too late, and they will be overblown and show their centers. Dahlia flowers also tend to open quickly, so be sure to harvest in the morning or early evening when temperatures are at their coolest, and place them immediately into water.
Dahlia stems can also begin to open faster if the flowers are exposed to sunlight, so be sure Dahlias aren't left in a sunny window or by a constantly opened and closed door.
Some, sear the tips of dahlias when harvested to extend vase life. To sear the ends, boil a pot of hot water and dip your freshly cut stems in hot water, around 150-160F. Storing in a cool location for 12-24 hours in a flower cooler can also extend the life of Dahlias.
Do Dahlias Come Back Every Year?
Dahlias are both annuals and perennials. In Zones 8 and higher, Dahlias can grow as perennials. In Zones 6 and 7, many people overwinter their Dahlias by putting a 3-4 inch layer of mulch, pine straw, or leaves over the top to help insulate them. While many find success, it can still be a risk. Dahlias grown in Zones 5 and lower are grown as annuals and need to be harvested and stored over the winter months until the ground is back above 60F for planting.
The End of the Season
Dahlias will continue blooming until the first frost or the end of the growing season. Having finished blooming, it is time to harvest the tubers or prepare for winter. The dahlia tubers will be just below the surface of the soil. Cut the plant about 4-6" above the soil.
If you are overwintering your dahlias, you can leave them in the ground until next season; simply cover them with a few inches of mulch, pine straw, or leaves; and allow them to rest until next Spring.
If you are harvesting your tubers, wait for 7-14 days and allow your dahlias to harden or cure for up to two weeks before harvesting unless under threat of extreme cold or heavy rain. Gently dig them up with a garden fork or spade, taking care not to damage them.
Cleaning Dahlia Tubers for Storage
Wash, and allow your tuber clumps to dry in a cool, shaded place for a few days before storing them in a cool, dry place, ideally between 40-50F. Whether you divide in fall, spring, or not, make sure your tubers are completely dry before storing them.
Multiplying Your Dahlias: How to Divide Tubers
Even if you don't do it yearly, dividing Dahlia tubers is necessary to keep them healthy and grow well. Dividing tubers is the best way to grow your garden. Dividing Dahlias can be done in either fall or spring, but always wait until your Dahlia plants are completely dormant before dividing them.
Fall is typically considered the best time to divide Dahlias when the Dahlias are in full dormancy. Still, in some cases, Dahlia enthusiasts divide them in late winter or early spring, arguing that it is easier to see the eyes of the plant.
Growing Dahlias: How To Store Dahlias Over Winter
Dahlias are best stored in a cool, dry place, ideally 40-50F. Dahlia tubers can be kept in the basement or garage for up to 6 months with success. Dahlias are stored in lots of different mediums. Some Dahlia enthusiasts use vermiculite, cedar, pine straw, peat moss, or sand. Dahlias can be stored in a bin with a small amount of soil to help insulate the tubers from temperature fluctuations.
Other growers use the saran wrap method, where individually dividing Dahlia tubers are placed in saran wrap and kept apart to prevent rot before storage.
Checking in With Your Tubers
Dahlia enthusiasts have different opinions on how to check their Dahlias, but all agree that it's good practice to take a peek during the winter months. Some Dahlia gardeners "dig around" in the tubers or feel for rot or mold growth. Dahlias stored should be checked for mold growth.
Now... Get in There!
If you're feeling intimated or overwhelmed, don't be! We're here for you. While it can seem like a lot, and trust me, there is much more to learn. Dahlias are very forgiving plants. In addition, they are pretty easy to propagate, so there are ample opportunities for saving money and growing dahlias yourself, but more on that later.
If you found this beginner’s guide to dahlias helpful, we'd love to hear from you.
Thanks for reading, and happy gardening!
Coty.
