Starting Dahlias From Seed
Starting dahlias from seed is so much fun! Each seed is unique and can produce a dahlia variety that has never existed. Dahlias have eight sets of chromosomes so due to the genetics of a dahlia, each seed may not have the same color or form as the seed parent. I usually start my dahlia seeds 4 to 6 weeks before my last frost. I start my seeds in late March inside my basement. I plan to plant them in the ground around May 1st as my average last frost is April 20th. You do want to plant the seedlings after the threat of frost, or you will need to cover the plants to protect the seedlings from frost. It would not be advisable to plant your dahlia seedlings if there is a chance you will have temperatures below 45 degrees. These are warm season flowers, so they need nighttime lows to stay above 50 degrees. If you start the dahlia seeds too early, you will need to pot up the seedlings to a larger pot to grow inside until your weather is warm enough.
I use Sungro Propagation mix; however, any professional seed starting mix will be fine. The seed starting mixture is a fine mixture of peat, perlite, and vermiculite. Depending on how many seeds you are sprouting, you may want to use 6 cell plug trays or 72 cell plug trays. Johnny’s Selected Seeds or Greenhouse Mega Store have many different sizes of seed plug trays.
Not all fully double dahlia varieties are good seed parents so dahlia germination rates can be between 50% to 80%. Also, dahlia seeds do not all sprout at the same time. They can begin sprouting in 2 to 10 days; however, some seeds will take 14 to 21 days. It is how they survived in the wild to not all sprout at the same time. It can depend on your environment where you are sprouting your seeds too. If your room is cool, it is going to take longer.
I use the paper towel method to start my seeds. I buy the paper towels that have perforated ½ sheets. I wet a small stack of 3 or 4 sheets. If you wet them under the faucet, you will need to gently squeeze out the water. You may want to just spray the towels with water using a spray bottle. You don’t want the paper towels too saturated with water as you do not want your seeds to rot. If my stack of paper towels are too wet, I just add another sheet or two of paper towels to absorb some of that moisture. I put the seeds on one side of the paper towels and then fold the other side over the seeds.
One thing I like to do is lightly spray the dahlia seeds with a diluted mixture of 3% hydrogen peroxide. I mix 1 part 3% hydrogen peroxide to 2 parts water in a spray bottle. This should clean the seed and help prevent any mold. If your paper towels are too wet and your room has high humidity, you may see some mold develop. If this happens, spray the seeds with a diluted mixture of 3% hydrogen peroxide and change the paper towels.
I lay the folded paper towels on a plastic tray or plate. I cover the tray with plastic wrap to keep everything moist as you do not want the paper towels to dry out. I set the tray in a room that stays around 70 degrees. Dahlia seeds do not need light to germinate. If your paper towels start to dry out, spray them with a spray bottle of water. You do need to check on them daily after the 3rd day as they sprout quickly and the root of the seedling can start growing into the paper towels. Once they start to sprout, I gently remove them from the paper towels and transfer them to the prepared seed plug trays. You may need a heating mat if your room is cool. A heating mat helps to maintain a warm temperature at night to prevent damping off. I purchased an iPower 10"x20" seedling heat mat and digital thermometer online. Also, a humidity dome helps for the first couple of days to a week depending on your environment. You should be able to find heating mats and humidity domes online. You could make a little tent with plastic wrap over the tray to help the humidity.
If you do not want to use the paper towel method, you can place the seed in your seed plug trays with a seed germination mix and lightly cover the seed with a little vermiculite or additional seed germination mix. With the possible low germination rates, you may have empty cells.
Depending on the number of seeds you are germinating, you may want to set up a seed growing area. You can use regular fluorescent shop lights or grow lights. Shelving racks work great for seed germination. I have shelving racks with fluorescent shop lights in my basement that I have been using for several years.
I use both fluorescent shop lights for my seedlings and grow lights. I especially like the grow lights for when I pot up my seedlings. I can place all the seedlings on a table with the grow lights hanging above them. I purchased my four foot grow lights online at Amazon. It is a 4 pack of lights. They are called Barrina LED Grow lights that are 4 feet long, 168W (4x42W, 1000W equivalent), full spectrum.
My husband attached the lights to a homemade frame that he made. I have the lights in my basement hanging over a table. They work great for when I pot up my dahlia seedlings or dahlia cuttings, and I intend to grow them inside for a month or so. I have used them for several years now. (I may earn a small commission over time from qualifying purchases as an Amazon Associate). Here is a link to the lights.
I purchased an AgroMax 2 foot light rack from HTG Supply Company that I use in my spare room. I found a similar small rack at my local home improvement store also. I have ordered 2 foot grow lights online; however, I am currently using a light kit from my local Lowe's Home Improvement store called "Boost Lighting 22.0 in light black 16-watt full spectrum LED grow light Kit" which costs around $24.00. Those lights have worked really well for me. I find the full spectrum lights work great for overall growth. The lights can be on for 12-14 hours. I have mine set on a timer for 14 hours. I leave the seedlings under lights until they have 3 sets of true leaves.
Since I start the seeds 4 to 6 weeks from my last frost, I keep the seedlings in the 6 cell trays. Once they have a couple sets of leaves, I do give them a little fertilizer. Make sure you read the label as you may need to dilute it for fertilizing baby seedlings. Miracle Gro makes a product called Quick Start which is for seedlings and transplants. There are other products like Fox Farm Grow Big Liquid Plant food or Vigor Plant Booster.
If I do start a few dahlia seeds early like in February, I will pot them up to a 4-inch pot after they are 3 or 4 weeks old. The 4-inch pots will give the seedlings room to make more roots and start a little tuber.
When they have 3 sets of true leaves, they can go outside if your weather is warm. If the weather has not warmed up to around 50 degrees or more, then keep them under the lights inside. If you started your seeds early, you may need to transfer them to a 4” pot so they do not get root bound and can continue to grow into an established dahlia. I let them harden off in an area outside that receives morning sun and afternoon shade for at least a week before I plant them in the ground. If the night time lows drop below 45 degrees, I bring the dahlia seedlings inside to my garage or basement at night.
When I plant my seedlings in early May, the soil is nice and warm. I usually plant them deeply. If a set of bottom leaves is in the way, I just remove that set of leaves. You will need to keep your seedlings watered until they are established.
I do pinch the seedlings after they have 5 sets of true leaves. I pinch them back to 4 sets of true leaves. This will produce more branches and a bushier dahlia with more blooms.
It is good to give the seedlings a balanced fertilize once they are established in the ground. It is helpful to take a soil test in your flower garden to know your phosphorous and potassium levels. I use an organic fertilizer like Espoma Plant-tone which is 5-3-3 with calcium and beneficial microbes. My soil has adequate phosphorous and potassium levels as I use a lot of compost each year. I find dahlias appreciate that little boost from fertilizer early in the season. I use it when I plant my dahlias. Again, if your dahlias are not growing well, it is good to take a soil test as you may need a fertilizer higher in phosphorous and potassium.
The seedlings will bloom during the summer and produce tubers just like dahlias planted from tubers. Remember to deadhead your dahlias, as the more you cut the dahlias, the more blooms they will produce throughout the summer and into fall.
When it is time to dig up your dahlias, you can store the tubers in a location that does not freeze. It is good if the temperature stays below 55 degrees to keep the tubers from sprouting too much. Dahlia tubers store better at 40 degrees to 50 degrees.
These are dahlias from seed that I was evaluating one year. Dahlia hybridizers evaluate their dahlias from seed for at least 3 years. After the third year, if the form and color is staying consistent, the hybridizer will start producing more plants. They may enter the dahlia seedling at a state fair or ADS dahlia show to receive more feedback.
It is so much fun growing dahlias from seed since you do not know what type of bloom you will have as they usually are different from their parent plant. It makes it very interesting each day to go into your dahlia garden to see what is blooming! In the fall, let some of your dahlias bloom and do not deadhead so that the bees can pollinate some blooms. It takes 4 to 6 weeks for the seed pod to close and become very firm with seeds. If you are not able to save dahlia seeds from your own dahlia garden, I do have dahlia seeds for sale usually in December; however, they are limited. I usually save seeds for my own breeding purposes. If you can, try to save some dahlia seeds from your garden. Good luck with your seeds!