Breeding dahlias can result in surprising, desirable and unique dahlia varieties, and it’s an activity any home gardener can do. To explain the basics of raising dahlias and her advanced techniques for hybridizing dahlias, joining me on the podcast is Kristine Albrecht, a dahlia expert and the founder of Santa Cruz Dahlias.
Kristine is the author of “Dahlia Breeding for the Farmer-Florist and the Home Gardener: A Step by Step Guide to Hybridizing New Dahlia Varieties From Seed.” She operates her no-till, organic dahlia farm in California, where she grows more than 1,500 dahlia tubers each year. She continues to work to create new dahlia varieties with complex colors and multiple forms.
Kristine is a past president and current vice president of the Monterey Bay Dahlia Society. She earned the American Dahlia Society’s Derrill Hart Award and Lynn P. Dudley Award in 2014 for her cultivar KA’s Cloud and won the Derrill Hart Award again in 2018 for her cultivar KA’s Khaleesi.
It’s super exciting to imagine what your hybridization project will result in, and that’s half the fun. Kristine describes it as a numbers game: If you plant 1,000 seedlings, you may get only 10 plants that you’ll want to keep.
Kristine began growing flowers to place in the rooms of her family’s bed and breakfast. Her friend gave her a handful of dahlia tubers that proved to be a hit, and the next year, she grew 60 tubers. She kept on expanding the breadth of her dahlia collection until getting up to the 1,500-per-year pace, on just a quarter acre.
Dahlias are super-prolific and like to be cut. When cut, they will give more blooms and will produce better tubers, Kristine says. Smaller varieties can give up to six blooms a week, and with luck, the giants can give a couple blooms per week.
If you would like to read Kristine’s full explanation of how to breed dahlias and her growing tips, check out the show notes from the original presentation of our conversation.
Before proceeding any further, I’d also like to pause to remind you that I have a new book out, “The Vegetable Gardening Book: Your complete guide to growing an edible organic garden from seed to harvest.” This book has insider tips and new-to-you information that will help you step up your gardening game and tackle challenges.
When and Where to Grow Dahlias
Dahlias perform best when they are planted in great soil, watered well and pinched off regularly. Kristine finds that the best place to grow dahlias is where you have previously had success growing tomatoes.
Dahlias require six to eight hours of direct sun a day, deep mulch and cool roots. Plant the tubers after the last frost date has passed and the soil temperature has reached 50°F. Plants should be 16 to 24 inches apart and will require staking, as they can grow to be several feet tall.
Dahlias like it hot, but not super-hot. Cultivars do well in coastal California and the Pacific Northwest, but to grow dahlias in a hotter area, you should install 30% shade cloth over them to cut down on heat while still allowing adequate light to get through.
Some growers in super-hot climates start their dahlia tubers super early. Then, during the hottest period of the summer, they cut the dahlias back to the ground. In fall, the dahlias will sprout again.
Because dahlias are frost sensitive, they are a challenge to grow in areas with a short growing season. The tubers can be pre-sprouted to give them a head start, or rooted cuttings can be used. The plants may still need to be protected with row cover early on to protect them from frost. If the tubers are started too late, the first frost of fall may kill the plants before they can flower.
Dahlias, for the most part, have beautiful colors and are double-flowered, but that’s not the case with all dahlias. The earliest dahlias came from Mexico, Central America and South America, and they were very basic looking. When Europeans collected dahlias from the Americas, they brought them home and started hybridizing them. Selective breeding gave us the dahlias that we know today.
Most plants are diploids, which means they have two sets of chromosomes, while dahlias are octoploids, with eight sets of chromosomes. “Because of the genetics they have a lot of diversity, and that’s unusual in the flower world,” Kristine says. That’s why there are some dahlias that have blooms that are under 2 inches and similar in appearance to cosmos and others that are 16 inches across, fully doubled, with petals going back to the stem.
Kristine joined a trip to Mexico for the American Dahlia Society Genome Project to collect wild dahlias for genetic sequencing. The project aims to discover if straight species dahlias have less DNA than the big, fully doubled dahlias on the market today.
Sprouting Dahlia Tubers Early
If you plan to sprout dahlia tubers indoors for a head start on the growing season, the timing will depend on the variety. Determine how long the variety takes to sprout and then count back from your last frost date. Some varieties sprout in just 10 days, while others can take as long as six weeks.
Not only does pre-sprouting give you a head start, but it also reveals which tubers are good and which are duds. The size of a dahlia tuber does not matter. A tuber will grow to produce flowers as long as it has an “eye” and is not damaged or rotten. Plant the tubers in slightly moist potting soil and keep them in a warm room. The tubers can start out without grow lights, but once they sprout they will require light. Kristine keeps lights on for 14 hours a day.
Pre-sprouted tubers can be watered right away once planted in the ground. That’s because they already have a root system to take up water. Unsprouted tubers shouldn’t be watered immediately because the tubers will just get wetter and wetter, which will make them vulnerable to rotting.
Pinching Off Dahlias
To get bushier dahlias plants with more flowers, pinch off the tip of the stems before they get tall. Kristine pinches off her plants once they have three sets of leaves, which is when the plants are about 6 to 8 inches tall. Other growers wait to pinch off until the plants are in the ground and the stems are knee-high.
Overwintering Dahlia Tubers
In warm areas, dahlia tubers can be overwintered in the ground. In areas where the ground freezes, tubers must be deep mulched or dug up and stored to survive.
Even where freezes are not an issue, the American Dahlia Society recommends digging up the tubers every fall so they can be divided before they are replanted. Tubers keep multiplying underground and form a big clump so it’s very crowded for the plants and they struggle for resources. Crowding also makes dahlias more susceptible to powdery mildew. If you do overwinter tubers in the ground, the American Dahlia Society recommends breaking off all but two stems per clump to prevent crowding.
When storing dahlias tubers, the best temperature is 43°F. Too cold and the tubers won’t survive. Too warm and the tubers will think it’s spring and sprout prematurely.
Dahlias reproduce through both seeds and tubers, and can even be grown from cuttings, but tuber propagation is the most popular way to propagate dahlias. All it takes is digging up and dividing tubers each fall.
Tuber propagation and cutting propagation are both methods of cloning which means the offspring will be identical to the parents.
To propagate a cutting, you can use rooting hormone powder, but it is not necessary. The cutting must include a leaf axis, the place where leaves meet the stem, because that is where roots will form. Plant the cuttings in rooting cubes, washed play sand or seed-starting mix.
Propagating dahlias from seeds is unpredictable than cloning. Each seed in a dahlia head needs to be pollinated individually. That means one dahlia seed head can have hundreds of different pollen parents. You can’t know what you’ll get when growing dahlias from seeds. “You could get yellows, reds, purples — all different colors,” Kristine says.
If you haven’t already listened to my conversation with Kristine Albrecht about breeding dahlias, you can do so now by scrolling to the top of the page and clicking the Play icon in the green bar under the page title.
Do you have experience breeding dahlias? Let us know in the comments below.
Links & Resources
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