How we grow dahlias
Dahlias are definitely worthwhile in your garden or landscaping. They bloom in the fall when most of the garden is looking faded and tired. Their blooms are often rich in color and loaded with petals which adds a lot of interest and flare in the garden. They are also a rewarding plant to grow as they multiply often in a single year, so you will have more to plant or share the following year.
I am not an expert, and there is plenty of information on the internet these days. Still, I get asked about my growing practices, so I have written this blurb of information on dahlias. I have mostly learned how to grow them through others sharing information with me, so it only seems fair that I pass this information along to you too.
I have grown dahlias successfully for 6 years, and plan on growing 2000 plants in 2024. There are many ways to grow dahlias, but this is what's worked for me.
Dahlias are a bushy herbaceous plant that produces showy flowers in the fall of all colors and sizes. Native to Mexico, these plants produce tuberous roots which can be dug and are easy to propagate with. Tubers are starchy bits of root (think: potato) that can be planted to produce a clone offspring from the mother plant.
The plants have been breed endlessly and now come in all sizes for different uses in the garden, from 12 inches to over 6 feet tall. Dahlias do produce seeds like most plants, and you can grow them by seed with lots of success. Dahlias that are grown from seed often have features that are similar to the parent stock, but will have unique traits separate from the parent plants (just like you don't look/behave exactly like your parents). Dahlias grown from tubers of a mother stock plant will produce an identical plant from the parent stock.
For a more consistent crop, we grow only via tuber.
Dahlias are hardy in zones 8-10. This means that if you get cold winters below 10 degrees F, your plants might not survive the winter. Dahlias can be grown successfully in colder hardiness zones by digging up the tubers and storing safely over the winter.
Dahlia tubers should be planted after all risk of frost have past. Planting any earlier involves risk of frost damage on foliage or possibly tuber rot if soil temperatures are below 60 F. We are in zone 6A here in Kittanning, PA and plant out tubers around Memorial Day.
Plant tubers on their side with the eye buried but aimed towards the surface of the soil. Bury tubers 2-4" deep. Don't water them in! Rain is fine as long as you have decent draining soil. We only water unsprouted tubers during unusually dry spring conditions.
Dahlias grow into pretty large bushy plants, so give them at least one square foot of garden space. We plant in double rows that are 4 feet apart, 1 foot spacing in the row. This creates a thick dahlia jungle by August that some people find too crowded. With some plant management, this has worked for us though.
Dahlias prefer a looser soil and are heavy feeders. We fertilize heavy in the spring with finished compost and bone meal. We do not fertilize again during the growing season.
It may take a few weeks for dahlias to sprout. Be patient, and dig them up to check on them if you're curious on how they're doing.
Summer Dahlia chores:
Once the dahlias have popped out of the Earth, water regularly through the summer. Dahlias don't compete great with weeds, so keep the garden bed free from weeds. We use reusable weed fabric to suppress weeds.
When the plants are roughly 6 inches tall, pinch the sprouts in half to encourage a bushier plant with more stems/blooms.
Dahlias grow to be big bushy plants, and often need supports. Some varieties do okay without support, so check to see how big the plants will get. In July, we go through and add supports.
There are many ways to support your dahlia plants. If you only have a few plants, you can use stakes and twine (1 stake per one plant). I've also seen people use tomato cages successfully. We plant in long rows, so we use hortanova netting and the corral method.
Inspect your foliage during the summer for signs of disease and cull any sickly plants. Many diseases can spread between plants (and some diseases spread to infect other plant species), so remove anything that looks suspicious to prevent widespread disease. Be sure to sterilize your tools as to not spread potential diseases.
Fall dahlia chores:
Our dahlias begin to bloom in July, and are fully productive from August-October. Most varieties will bloom until frost. To ensure a healthy plant during blooming season, dahlias should be cut or deadheaded regularly. Cut the blooms when they are fully open, and cut stems at least 12 inches long.
With busy plants, air circulation becomes a problem and invites diseases and pests. We strip the plants from ground level to 8-12 inches high simply by removing foliage and unruly side branches. See picture below.
Very important: if you plan to dig/save your tubers, now is the time to identify and label each plant so you know what you're digging up later on.
Winter dahlia chores:
***If you live in a warmer climate, you can leave your dahlias in the ground over winter. In cold climates, you must dig them up in the fall/early winter. Alternatively, dahlias can be grown as an annual--meaning you can let the winter kill the plant and plant new next year.***
After the first frost, dahlia plants will turn brown and look sickly. We mow them down to just above ground level. I typically let them "cure" in the ground for a couple of weeks. This seems to harden off the tubers a bit, and it assists in eye formation too (making it easier later on).
When ready to dig tubers, dig in a wide circle as to avoid damaging the tubers which can stick out 12 inches from the stalk. Loosen the soil around the tubers until you're able to pull out the plant. Knock loose (gently) as much soil as you can, and take them somewhere safe from freeze/frosts.
How to store dahlia tubers?
There are many different ways to store tubers. I have found a way that works for me, and I encourage new growers to try 2 or 3 methods and see how their tubers do over the winter. This way may not work for everyone.
I dig, wash, and divide tubers in one day.
When dividing, your tubers must contain an eye and a substantial tuber for energy storage. Be sure to remove any damaged/rotting bits of tuber, and do not keep anything that looks diseased. Rinse your tools frequently in a diluted bleach solution to help prevent spreading plant diseases.
I store mine in peat moss in air tight totes, and they are kept dark and consistently around 55 F. Colder would be better, but my tubers do fine at this temperature. Avoid freezing temperatures and damp conditions.
Dahlias are a worthwhile garden endeavor, and I hope you find a system that works for you. If you have other questions, you can contact me at firstname.lastname@example.org. I love chatting about dahlias. :-)