How to Grow Dahlias in Wisconsin

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Here are my research-backed tips for how to successfully grow Dahlias in Wisconsin.

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I live in southeastern Wisconsin, so I am in Zone 5. We have long, cold winters and short-lived summers, so our grow-periods are very short. But it is still possible to grow beautiful flowers and tons of veggies!

I bought seeds from Eden Brothers and I am so excited for them to arrive in the mail!

If you have a plan ready to go, you can safely plant your Dahlias in Spring and enjoy continuous bloom from mid-summer to the first fall frost. Here are my research-backed tips for how to successfully grow Dahlias in Wisconsin.

All About the Dahlia Flower

Dahlia flowers are one of America’s most popular flowers. They grow in gardens all across the country. Dahlias offer more variety to choose from than most other types of flowers, coming in varied shapes and sizes, ranging from flower heads as small as quarters to others as significant as dinner plates, flowers with colors and patterns that move through the full range of the color pallet.

Choosing the right types of dahlia flowers for your garden might be the hardest part. Their many unique features make dahlias one of the most versatile flowers because there is a dahlia to suit any taste. They are a late-blooming flower and provide color and shape to the garden- as well as food to the bees- long after many other plants have stopped flowering for the season. Autumn is the time of year when all the hard work of raising them pays off, and your plants reward you with beautiful flowers for fresh bouquets.

growing dahlias in wisconsin

Dahlia Planting Tips 

  • Take care when planting dahlias in Wisconsin. Don’t plant them until the evenings stay well above freezing and the soil has warmed up. Zone 5 has a medium-short growing season compared to others in the USDA garden zones. Our last frost date is around mid-May, and our first frost date comes around late September to early October.
  • They require remarkably little water in the early stages. Many have success watering the tuber once after planting and waiting until the tuber has sprouted before watering again.
  • In most cases, dahlias only need to be watered two to three times a week. Don’t hit them with the hose or any other hard or heavy stream of water, especially when they are flowering. Sprinklers and drip systems work best.
  • Depending on the plant’s size, the tubers should be planted one foot apart for smaller growing varieties and up to three feet apart for larger dahlias types.
  • Use a low nitrogen soil mix to avoid the risk of tuber root and underperforming flowering.

use growing zone map

growing dahlias in wisconsin

How to Care for Dahlias

  • Make sure to fertilize lightly during the mid-summer through late autumn to get the best flowers out of the plants. Avoid over-fertilizing and fertilizer with high nitrogen content.
  • Like most tuber plants, their roots are vulnerable to rot and disease. Avoid over-watering and plant in well-draining soil to help avoid this issue.
  • Dahlias have a few pests and predators. They are susceptible to mites, aphids, cucumber beetles, slugs, and deer. There are many options to deter and mitigate them. Use the method you are most comfortable with, but if you decide to use a pesticide, make sure not to use something lethal to bees and void spraying the plants once they have flowered to help keep the bees safe.
  • Dahlias aren’t great in the cold. Planting the tubers too early can stunt their growth or kill them if they freeze. Here in Wisconsin, dahlias may be treated as annuals and can be grown again every year.

growing dahlias in wisconsin

Overwintering and Replanting Dahlias in Wisconsin

If you don’t mind planting Dahlia’s as an annual, then overwintering isn’t necessary. Overwintering dahlias ensures the flowers you love will be there year after year. They are plants that don’t handle brutal winters well. According to the USDA, Dahlias are only cold hardy down to zone 7. Growing dahlias in Wisconsin’s gardens – which range from garden zone 3b in places like Douglas and Sawyer to zone 5b in Kenosha and Milwaukee- means putting in extra work during the wintertime to make sure that they survive and can return next year.

When your dahlia plant has started to die back at the end of the growing season, and the first frost has hit, cut the plant back so that its main stems only come a few inches out of the ground. If you have multiple verities of dahlia in your garden, now is an excellent time to label them. Then the root ball and tubers need to be extracted from the ground.

Depending on the plant’s size, the root base can be upwards of a foot wide and a foot and a half deep. Make sure that you start digging far enough out to get the whole root base out and intact. Let the root ball dry out a little before finding a cool and dark place to store them for the cold winter months. Replant the root bases in the Spring, usually after Memorial Day, to make sure it’s warm enough. The roots will retake, and the dahlias will come back bigger than they were the year before.

Helpful Resources for Growing Dahlias 

grow-wisconsin-dahlias

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