You're Not Growing Dahlias in Your Garden? That's Criminal!
Oct 18, 2018
True crime is a big deal these days. Most people have heard of the sensational murder of Elizabeth Short in January 1947. News reporters dubbed her the "Black Dahlia," and to this day, podcasters and online crime buffs obsess over this famous Los Angeles "whodunnit".
This is the awkward moment when we try to dig ourselves out of a hole and segue into the subject of, well, planting dahlia. And, umm...keeping them alive.
Dahlia, in spite of rumors and innuendo, aren't difficult to grow from seed. Most of the drama associated with cultivating award-winning dahlia plants stems from the mistaken assumption that, because of hundreds and thousands of enthusiasts who nerd out on their own cultivation techniques, dahlias must be temperamental little divas.
A Brief History of Dahlia Variabilis
According to the U.K.'s National Dahlia Society and several other non-Wikipedia sources, dahlias were first imported from their native Mexico to Europe by way of the Botanical Gardens in Madrid in the latter part of the 18th century. Spanish botanist Antonio José Cavanilles (a.k.a. Abbe Cavanille) named the genus for his contemporary, Dr. Anders Dahl (1751-1789), a countryman and student of the Godfather of Botany, Carl Linnaeus. (Not to be confused with Uncle Pliny the Elder).
While it's perfectly acceptable to call them "dahlias," the correct term is "dahlia." Just don't hold us to it if we slip up once in a while. You'll also note that when we're specifically referring to botanical names, we'll use italics.
Or maybe our fonts just look tipsy because we are too.
The Gardener's Obsession with Dahlia
If you google "dahlia" and get past all the links to Ms. Short, you'll find a metric manure ton of gardening clubs specifically formed to celebrate this wildly popular garden ornamental. There are so many species, varieties, and hybrids, the plant is easily able to draw crowds at national garden shows and competitions focused on the genus alone. Many countries and U.S. states boast their own dahlia societies. Do an internet search relevant to your location, and chances are you'll find events and enthusiastic mentors in your area. Here are only a few of the national organizations:
- The American Dahlia Society (U.S.) with links to and news from state clubs
- The National Dahlia Society (U.K.)
- The Dahlia Society (Canada)
- National Dahlia Society of New Zealand
If you grow dahlia plants in your front yard, you're likely to meet at least one neighbor who wants to ask you about the variety or share a story about a relative who created their own cultivar. Or, you might get asked "what kind of flower is that?" because dahlias bloom in so many colors, patterns, shapes, and sizes, they can be unrecognizable to even the most wizened gardener.
Aside from the endless variability within the Dahlia genus, aficionados take pride in their personal techniques for growing and caring for their plants. Dahlia fanatics can get a little tiresome after the third hour of an over-the-fence gardening consultation, but the plants themselves? Never.
Dahlia in the Garden
"Black Dahlia" referred to Elizabeth Smart's raven-colored hair, not to any particular dahlia variety; there aren't any true "black" dahlia flowers. But these plants bloom in most any other hue, many being bi-colored—pink, lavender, yellow, white, gold, and red.
Dahlias are easy plants to grow and yield beautiful blooms from mid-summer through fall. In many respects, 'dahlia culture' is similar to 'tomato culture.' If you can grow tomatoes in your garden, you can successfully grow dahlias.
— The American Dahlia Society
Note that the following general tips for selecting the right site for dahlias in your garden are just that; check the back of your dahlia seed packet to nail down your selection's specific requirements and characteristics, and be sure to double-check our catalog so you get a size and color suitable for your garden scheme. There are dwarf varieties, giants with plate-sized flowers, and everything in between.
USDA Hardiness Zones & Ideal Environment
One would equate Mexico to intensely hot and dry weather. But Mexico has mountains, and dahlias are native to cooler elevations around 3000'. Don't let the tubers confuse you; dahlia are annuals. In Zones 7 to 10 it's okay to leave their tubers in the ground over the winter for new blooms in spring, but everywhere else, you'll want to dig them up and store them indoors (more on that later). Here are dahlia's other needs:
- Sunlight Preferences: Full sun in all but the hottest areas, where they like some light afternoon shade.
- Watering Requirements: Consistently moist, but not wet. Don't allow them to dry out!
- Soil Preferences: Well-drained, loose soil of average richness.
- Soil pH: 6.5 to 7.0 (slightly acidic).
We recommend preparing your dahlia beds by deeply (about 12") turning the earth and—if your soils are noticeably depleted—incorporating some well-aged compost. Otherwise, skip it. If your soil is alkaline, add a bit of peat moss...or your preferred peat moss alternative.
Are Dahlias Good Container Plants?
Absolutely! You'll want to choose a dwarf variety, or deep containers to accommodate standard dahlias. Take extra care in watering since container plants can dry out quickly.
You can bring your dahlia containers into a protected building to prevent the tubers from freezing in their dormancy, and set them back outside when the weather warms in spring.
Dahlia's Signature Characteristics
Most dahlia plants, if you stand back and squint, look like upright, conical, miniature deciduous trees. Each plant grows from a central stalk, with broad, arrow-shaped, moderately-serrated leaves attached to graceful branching stems. The flowers grow singly or in clusters at the top of the plant structure, with some variances; a few varieties have low-growing foliage and tall, flowering stalks, for example, and plant stalks often fork naturally for higher flower production. Or you can pinch them back to promote fuller, flower-ier (is that a word?) plants.
- Bloom Period: June through September, depending on variety and climate.
- Days to Maturity: Dahlia plants typically bloom in 60 to 120 days; 90 for standard-sized varieties.
Aside from pointing out that dahlia are in the Asteraceae family, characterized by having central disks and ray florets as do other composite flowers, it's difficult to limit them to a single description. Dahlia varieties may have a single layer of petals, or they might have so many they look like dense, round, ruffly pom poms.
Maintaining Your Dahlias
Too much compost or manure at planting causes problems, but if you apply a low-nitrogen fertilizer (5-10-10, for example) each month through the growing season, you'll boost your blooms and put you in the running for your local dahlia society competition.
Snails, slugs, and aphids are big fans of dahlia foliage, so plan your strategy for fending them off. Deer, on the other hand, aren't particularly interested in these plants. They'll eat them if nothing else is around, but they'd rather go after your prize roses.
Deadheading spent flowers during the bloom period encourages continual growth.
Storing Dahlia Tubers Over Winter
This part is quite involved so we're only going to go over the rough basics. Dahlias go mushy and their tubers go dormant after the first fall frost, and this is thought to be the best time to dig up their tubers. Colorado Dahlia Society warns you must dig them up before the ground actually freezes, so if winter falls faster than a gardener tripping over a rake do the following:
- Cut dahlia stems to 4" above the soil surface when the plants begin to wilt (to both clean up and mark the spot)
- Mulch snugly around the base of the plant to prevent the soil from freezing
- Dig up the tubers when you and the weather are ready to go for it.
Dahlia tubers look like clusters of small, root-covered sweet potatoes. Use a garden fork to gently loosen the soil around the plant base about a foot deep, and a foot radius around the stem, at an angle. You want to avoid damaging the roots or (as what happened to poor Elizabeth Short) cutting the tubers in half.
Once you've loosened the soil, gently lift the tubers. Knock off any excess dirt, and follow the cleaning and storing steps outlined on this American Dahlia Society page.
In the meantime, we'll be sipping hot cider and cheering you on from the sidelines. We take the easy route by growing new dahlia plants from seed each year.
Growing Dahlia from Seed
Starting a dahlia garden from tubers is a risk if you don't trust the parent plant's vigor, or they're incorrectly divided and stored. Soil-borne pathogens can contaminate your own garden. The most common concern, if you don't have a trusty dahlia gardener in your social circle, is the cost of sourcing dahlia tubers from catalogs or gardens.
Some of us just appreciate the challenge and satisfaction of truly starting from scratch.
Seed Treatment: None required.
When to Plant Outdoors: Direct-sow your seeds after all danger of frost has passed.
When to Plant Indoors: 6 to 8 weeks prior to the last frost; only plant them in biodegradable pots as D. variabilis roots are very sensitive to transplant shock.
Seed Depth: 1/4"
Seed Spacing: 12" to 16" depending on the variety.
Days to Germination: Dahlia seeds typically begin sprouting within 7 to 14 days at about 70°F, but note, they won't sprout all at once and some might drag their heels a bit.
Transplanting Tips: Again, we recommend starting your dahlia seeds in peat pots or CowPots. You'll want the young plants to attain about 6" of growth and undergo about 10 days of hardening off before you plant them in their outdoor beds.
Be sure you keep your seedlings and transplants evenly moist when growing dahlia from seed until they establish their root system!
Are Dahlia Plants Safe? Are They Edible?
In Mexico, the dahlia plant's crisp tubers are valued as an emergency source of carbohydrates and, thanks to their high moisture content, a means of combating dehydration. Dahlia tubers' flavor is described as a bland combination of potato, celery, turnip, and carrot.
The high levels of inulin contained in dahlia tubers can cause severe intestinal upset and impressive flatulence in humans and, according to the ASPCA, are considered mildly toxic to pets for these reasons and the potential for skin irritation. Poison.org doesn't include dahlia in their database of poisonous plants.
As always, take caution when you experiment with new homegrown menu items, or at least when you're walking behind someone you just served fresh or cooked dahlia tubers.
Dahlia tubers are a rich source of potassium, so if you're stuck on an arid Mexican mountainside and you forgot to bring your horchata and bananas, look for a wild dahlia plant to put some pep back into your step. Raiding a cactus for its juice is actually a far more efficient way to make yourself sick, despite survival folklore. Raiding the tubers grown from our "cactus dahlia" mixture is a safer bet.
But our attorneys advise you take plenty of water along when you visit the desert and eat dahlia tubers at your own risk.
Source Your Dahlia Seeds from Seed Needs
Since we're seed specialists, we don't carry tubers and bulbs. What we do carry are fresh, high-quality dahlia seeds selected from vigorous, proven genetics and reputable, sustainable producers.
Remember, hybrids aren't the same as genetically-modified organisms (GMO). Gardeners have been hybridizing veggies, fruits, herbs, and ornamentals for thousands of years. It's why we have so many spectacular types of dahlia, and why we're able to offer you varieties we feel will give you the best introduction to this beloved garden annual.Contact us if you'd like more information, or if you'd like to suggest a particular species or variety for our catalog!