Dahlia tuber question

unclehead_gwApril 23, 2013

I hope teddahlia or another experienced dahliaholic can answer this question. I grow 50-60 dahlias each year and don't have enough room to start them in pots. I always direct plant tubers. Our last frost date is mid-May and I usually wait another week to be safe. The weather hasn't been kind the last couple years (rain) and sometimes I'm planting into June. Since I'm not starting a plant, if I were to plant the tubers a week or so earlier than our last frost date, how cold would it have to get to hurt the tubers planted 4-5" deep? I'm assuming the sprouts wouldn't be through the soil for a couple weeks. I didn't have blooms last year until September and I"d like to speed the process up a little.

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It would take a frost of about 20 degrees to kill a tuber that is buried 4-6 inches under the soil. Planting a week or so ahead of the average last day for frost should be no problem. I would as a precaution check the long term forecast for really bad weather. Dahlias like the soil temperature to be about 60 degrees( average of high and low for the 24 period). But they will start to grow some roots and get ready to grow if the soil is a bit cooler.
People who start them in gallon pots move them around in their yard and garage. Out for warm weather, in for cool weather. Sounds a bit obsessive compulsive, but you will get much earlier blooms....

    Bookmark   April 23, 2013 at 7:02PM
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Thanks for answering my question,Ted. I can't wait to get these tubers in the ground. Hopefully,this year will be more dahlia-friendly and not like the last two years of record rainfall followed by near-record drought.

    Bookmark   April 24, 2013 at 8:57AM
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steve22802(7a VA)


Another approach you could try is to plant all your tubers close together in a shallow tray as is sometimes done in cutting propagation. You could start them this way 3-4 weeks early and get them to break dormancy and put up a sprout and a few leaves. I think this would get you a nice head start over sticking a fully dormant tuber into cold outdoor soil.

Look at this page:

Notice in the first picture that there are close to 30 tubers in the flat and it's only about half full. So you would only need to find a few square feet of warm sunny indoor space. I would use a loose soilless mix to make it easier to pull them apart when it's time to plant them out. If the roots get too entangled to easily pull apart you could just cut the tubers into separate root balls by snipping between the tubers with shears.

You could also try warming the soil in your planting bed a week before planting the tubers by covering it with clear plastic.

    Bookmark   April 25, 2013 at 7:54AM
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Thanks,Steve. Actually, I had thought about starting the tubers in a tray and I bought some trays a couple weeks ago. The trays are 24" long and about 6" deep. Maybe I could start them in a few inches of soil and add more as they grow. My only concerns were the possibility of the roots growing together if they were planted to close and also having the necessary amount of light. I do have some shop lights that I used to start tomato plants. Sounds like I will have a new weekend project. Thanks again. unc

    Bookmark   April 26, 2013 at 4:40PM
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steve22802(7a VA)


From the info in your first post it looks like you only have about 3 weeks until you will plant the tubers outside so you shouldn't worry too much about root entanglement or less than ideal light levels. They are not going to grow that much in the next 3 weeks, especially if they are totally dormant tubers. Go ahead and get them started even if they are packed close together as this should get you a few extra weeks of blooming time over the course of the season.

    Bookmark   April 26, 2013 at 9:40PM
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