Dahlias Through the Seasons: Autumn

The temperatures are dropping, daylight hours are shortening, and you are beginning to wonder, “What’s next for my dahlias?” First off, ENJOY those beautiful blooms because they will be gone before you know it.  Dahlias love cool nights and hit their stride September through the first frost. Autumn is not without its long list of dahlia tasks including one of the most physical, the DIG. Here is my Dahlia Autumn To Do List!

Cutting and Deadheading:

You have big beautiful flowers getting ready to bloom on your plants and wouldn’t it be nice to bring a few inside!  When you cut dahlias, it is important that the bloom is full and open. Unlike other flowers, dahlias will not open fully once cut. Early in the morning or late in the evening are the best times to cut dahlias because the plant is hydrated. Cut deep into the plant (yes, you will be sacrificing some side buds) to encourage it to send up another round of long stemmed beauties. 

Deadhead! If you want the plant to continue producing flowers, it is important to remove flowers that are spent.  You will be rewarded with more flowers for a longer period of time.

Troubleshooting Bloom Problems:

Caterpillars, tarnish plant bugs, cucumber beetles, earwigs, and Japanese beetles will eat dahlia blooms and petals. We use organza bags to protect our flowers from bud to cutting.  This is time consuming but worth it for the perfect blooms. If you decide to use a spray to manage insect pressure, be sure to research when and how to use it to protect as many of the beneficial insects as possible.

Dahlia bloom protected by an organza bag, just look at that perfection!

A bud that I missed covering which became a hungry caterpillars’ lunch.

Label:

Your flowers are blooming and you want to keep the tubers for next year. LABEL, LABEL, LABEL! Trust me, label your dahlias while the flowers are blooming. You will not remember once the frost comes no matter how many times you tell yourself that you will (done that several times.. ).  Labeling will help you plan your garden for the following year, make swapping tubers easier, and will help identify those tubers that you may want to propagate in late winter/early spring.  Tie a label onto the very bottom of the stem and make sure its snug, don’t want it to get lost during the DIG.

Wait, Water, and Enjoy:

Dahlias will continue to bloom until the first frost. Keep them well watered, 1-2 inches a week. Powdery mildew may begin to show up and there are a few remedies you can try to slow down its spread. I focus on early prevention like removing lower leaves to increase air flow, giving the plants compost tea for health, and removing infected debris from the garden. 

FROST:

Frost is in the forecast.  If it is a light frost, you may be able to cut off any damaged parts (buds and leaves) and the plant will grow back until there is another frost.  You can also try covering your plant on nights when there may be a frost to protect them.  In the end, a hard frost will send the plants into dormancy whether they have been protected or not. On the morning of a frost, get out early and check out your final blooms!  They will be beautiful as the sun touches their frost covered petals but, as the sun rises, the blooms will turn brown and mushy. Time for clean up.

*You do not have to wait for frost to start the dormancy process. If you wish, cut back your dahlias to several inches about the soil when you are ready, wait a week or two, and then dig up the clumps.

Cut Back, Wait, Dig:

After the frost has killed your plants, cut the stalks back to a couple inches above the soil line. Wait another week or two if possible before digging up the tubers. This will give them time to redirect their energy and to form eyes which is where the plant will grow from next season. The tubers need to be lifted before the ground freezes and makes it difficult to get them out (been there…). I have also dug them out in the middle of a snowstorm where I lost a good percentage of labels. Don’t be like me! Choose a cool sunny day to dig the dahlia tuber clumps out of the ground. 

Some plants make long tubers, other short and round. Some plants will have a dozen or more tubers and some will have very few. It all depends on the variety but a tuber with an eye (we will explore this in more detail later) will grow a plant in the spring if it makes it through winter storage. If you are planning to divide in fall, carefully shake off excess dirt and wash the tubers so you can see the eyes (where the new plant will begin to grow). Let the tubers dry and then you can begin splitting the tuber clumps. If you are dividing later (my preferred method), keep the dirt on the tubers as it will help them maintain moisture levels during storage.

Storage:

Unfortunately, dahlia tubers are the Goldilocks of flowers.  They can’t have it too warm or too cold, too wet or too dry, it should be just right.  And what is just right for me, may not be just right for you. I will share what works for me along with a few other methods that I know others have had success with.

The first question you need to ask yourself is divide now or divide later. Sometimes the eyes can be more visible on freshly dug tubers which makes it easier to divide the tubers into smaller more manageable pieces.  Should you choose to divide, storing tubers in bins or bags of vermiculite in the fridge, basement, or garage (temperature should be about 40-50 degrees) would be one option.  Other growers individually wrap tubers in plastic wrap and place in a cold (not freezing) place. I have been successful with vermiculite but not plastic wrap, which I also find wasteful and time consuming. Consider both methods and maybe try both to see if you prefer one to the other.

My preference is to divide in late winter/early spring. I have found that tuber clumps have a greater chance of surviving winter storage. If you choose the divide later method, keep in mind that you need to have a space large enough for all those massive, heavy tuber clumps.  I am lucky to have a bulkhead space that hovers above freezing even in negative temperatures. Keep the clumps off the floor by placing them in crates or plastic bins. I place my crates on a large piece of silage tarp which I wrap loosely around the crates and tubers. This keeps some of the moisture in and keeps it dark. I place a thermometer on top of the bins so I can monitor the temperature and humidity throughout the winter. Occasionally, I will check the tubers for rot, shriveling, or critters trying to eat the tubers. Rot indicates too much moisture and shriveling not enough (although, shriveled tubers can still grow). In the Winter post, we will learn how to divide your tuber clumps and to propagate those dahlias which you want more of!

Tuber Sourcing:

Dahlia farms, breeders, and larger dahlia suppliers will hold sales Fall through early Spring. If you have a specific dahlia you are looking for, you can use https://dahliaaddict.com to find a supplier. Many sought after tubers are sold out within minutes of going live so be patient and look for multiple locations. Swan Island is a large supplier and is easier to order from and their tubers are good quality. Another favorite dahlia farm is Summer Dreams Farm. They have great quality tubers although they can a bit more pricey. If you are looking for larger quantities, Dahlia Shed offer tubers in packs of 5.

Additional Resources:

Summer Dreams Farm has some great tutorial information available on their website. He is one of my favorites to learn from! If you are looking into learning about growing dahlias from seed, hybridizing or just some great content, Kristine Albrecht from Santa Cruz Dahlias is wonderful. Finally, Erin Benzakein of Floret Flowers has a new book on dahlias that provides a good overview as well as a list of many of her favorite dahlia varieties.

As always, I love to hear back from you all! Questions, comments, and ideas are welcome as conversations help us to grow and learn. Thank you!

So many to choose and all so beautiful!