7 things you should know about dahlias
Here are the most frequent questions I’ve been asked about dahlias on Instagram
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How and when do you start and plant your dahlias?
I live near Montreal, Quebec, Canada, which is USDA hardiness zone 5 [to know your hardiness zones in the United States, click here]. In mid-April, I start my dahlias indoor in root-making pots in pro-mix with mycorrhizae. As soon as they have few leaves, I try leaving them outdoor during the day and eventually overnight when there is no risk of late frost. Alternatively, I plant some later-bought tubers directly in the garden when risk of frost is passed. I have more success and earlier bloom with the first method.
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What is the soil requirements of dahlias?
Dahlias are happier in a rich, well-drained soil, slightly acidic. My own soil is a layer of sand over clay. I removed the sod along four to six inches of clay when I designed the borders, then I incorporated garden soil, and mixed the sand with peat moss and perlite. I make sure to continue adding peat moss and home made compost every year. Having started my tubers in pro-mix also enriches my soil yearly.
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Where do you plant your dahlias?
My two borders receive lots of sun, probably at least 6 hours a day. Dahlias may grow in a shadier location too, but may not bloom as much. In very warm climate (zones 9 and more), they could benefit of a shady location part of the day.
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How far apart do you plant your dahlias?
It all depends of where you plant them and the varieties you are growing. In a mixed border, with other perennials, smaller plants may look better at a short distance of each other (8 inches apart). I like having my dahlias for cut flowers at a distance between 18 and 24 inches. Because I use tomato cages instead of staking for taller plants, I make sure the cages do not overlap but I am OK if they almost touch. I leave some larger space in between some varieties to provide access to the middle of the border.
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How much water should I give my dahlias?
Dahlias are heavy drinker during the hot days of Summer when they are well-established, and should be provided with watering at least 2 to 3 times a week. Heavy rain and over-head watering may damage the blooms and accelerate wiltering.
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Should I feed my dahlias?
YES! After the dahlias have been transplanted for a week, I like providing a plant starter and leaf booster fertilizer such as the Jacks Jr 9-45-15, followed every 2-3 weeks from early July to mid-September by a low nitrogen, when buds are ready to appear, like J.R. Peters Jack’s Professional No. 4 10-30-20 Blossom Booster + Micro. A tomato fertilizer could be used instead, such as a 10-20-20.
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Do I have to uproot my dahlias in the Fall? If yes, when should I do it?
Dahlias are very sensitive to cold. Colder nights will affect immediately the flower production, with smaller flowers, often lighter in color, weaker stalks, wilting faster or breaking easily on the plant. I remove all flowers the day before a frost (let’s not waste one!), then dig all the tubers when the foliage turns black. Please consult the post about Fall dahlia care. If you do however live in warmer zones (7-10), you may want to inquire if leaving tubers in the soil is recommended in your area.
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