How to Grow Blue Mistflowers

Blue mistflowers with clusters of fuzzy purple-blue flowers and buds closeup

The Spruce / Adrienne Legault

The blue mistflower, also known as wild or hardy ageratum, is a wildflower known for its bright blue clusters of fuzzy flowers. These eye-catching blooms appear on top of purple-red stems adorned with green, triangular, toothed leaves. The flowers lack rays and have a fuzzy, airy appearance thanks to their long stamens. This is a fast-spreading perennial and can become invasive if left unchecked. The abundance of nectar produced by the flowers attracts many bees and butterflies. 

The plant should not be confused with Ageratum houstonianum, an annual bedding plant native to Mexico that is sold in the spring in the nurseries of home improvement stores.

Botanical Name Conoclinium coelestinum
Common Name Blue Mistflowers, Blue Boneset, Wild Ageratum, Hardy Ageratum
Plant Type Perennial
Mature Size 2-3 ft. tall, 1-2 ft. wide
Sun Exposure Full, partial
Soil Type Loamy, sandy, clay, moist
Soil pH Acidic, neutral
Bloom Time Summer, fall
Flower Color Blue, purple
Hardiness Zones 5-10, USA
Native Area North America

Blue Mistflower Care

These fuzzy flowers are perfect additions to pollinator or perennial gardens. They are quick spreaders and are often used as ground cover. If these plants grow beyond their designated area, simply dig up the unwanted rhizomes and move them to another desired area. You can also deadhead spent blooms to prevent the flower from going to seed. As these plants mature and reach their full height, they may require supports to prevent them from flopping over. 

These flowers are naturally found in moist areas such as meadows, ditches, low woodlands, or near water sources. Mimicking these conditions by keeping the soil moist will ensure a healthy blue mistflower. Common pests or diseases include powdery mildew, aphids, or leaf miners. 

Warning

This is a quick-spreading plant that reproduces through rhizomes and self-seeding. Because of this, the blue mistflower has invasive qualities and can choke out native plants. Though native to the central and southeastern United States, other areas of the country consider this an invasive weed. Do thorough research before deciding if this plant is right for your area.

Blue mistflower with triangluar leaves and thin stems with tiny fuzzy flower clusters in sunlight

The Spruce / Adrienne Legault

Blue mistflower with purple-blue fuzzy flowers and buds on top of thin stem

The Spruce / Adrienne Legault

Blue mistflower with purple fuzzy flowers with long stamens closeup

The Spruce / Adrienne Legault

Light

The blue mistflower grows best in full to partial sun. In extremely hot climates, partial sun is ideal, especially in the afternoon.  

Soil

These fuzzy flowers are tolerant of a wide range of soil conditions, including loamy or sandy soil, along with clay dirt. The key to survival for blue mistflowers is moist soil. Add a layer of mulch on top of the dirt to help retain moisture. 

Water

Since the blue mistflower thrives in moist soil, consistent watering is essential. This is especially true during times of drought or very high temperatures. However, these plants are somewhat drought tolerant and can withstand dry seasons without much harm inflicted.

Water the blue mistflower once the soil begins to feel dry. This may be once or twice a week, depending on climate conditions. 

Temperature and Humidity

The blue mistflower is a hardy plant and can handle both hot and cold temperatures, including winter and summer extremes. It is tolerant of a wide range of humidity levels as well. It's considered to be hardy in USDA growing zones 5 to 10, which is spans a large temperature range.

Fertilizer

Because this plant thrives in a variety of soil types, fertilizer is not essential for healthy growth. This plant does appreciate organic matter, so adding compost to the soil is a great option. If this plant requires extra nutrients, a well-balanced liquid fertilizer is a good choice in the spring and midsummer. 

Propagating Blue Mistflowers

Because the blue mistflower spreads so rapidly, propagation is very easy. This can be done by root divisions or by cuttings.

To divide by root division:

  1. Using a sharp shovel, cut through the underground rhizomes at the point you would like to divide the plant. Be sure each division has healthy foliage and its own root system. 
  2. Dig around the division until the plant can be lifted freely from the ground. 
  3. Transplant these divisions into another suitable area. 

To propagate with cuttings:

  1. Using clean, sharp garden snips, cut away a stem in the late spring. Be sure that the cutting has around 3 or 4 sets of leaves. 
  2. Trim away the bottom leaves. At this point, the cutting can be placed in either water or moist soil. If placed in soil, it is best to dip the cut end into rooting hormone. 
  3. Keep the cutting in a bright area and keep it moist. 
  4. Check for roots by very gently tugging on the plant. When resistance is felt, roots have likely formed.
  5. Transplant to desired garden location.

How to Grow Blue Mistflowers from Seed

To start blue mistflowers from seed, the seeds must go through cold, moist stratification. This is needed to enable germination and must be done for 1 to 3 months. To achieve this, keep the seeds moist by placing them in a sealed plastic bag with moist sand or a paper towel and place them in the refrigerator.

Another option is to sow the seeds in the fall to allow this process to happen naturally over the winter.

If the seeds are started indoors and have been cold stratified in the refrigerator, here is how to start them: 

  1. Sow the seeds on top of moist soil. 
  2. Place the seeds in a warm, bright location. Near a window or under a grow light is ideal. 
  3. Germination should occur in 7 to 10 days. 
  4. Once the seedlings are a few inches tall, harden them off and transfer them outdoors after the threat of frost is gone. 

To start seeds outdoors, follow these simple steps: 

  1. Sow seeds in the late fall to allow cold stratification to occur over the winter. 
  2. Once temperatures are warm enough in the spring, seedlings should emerge. Keep the seedlings moist.  

Overwintering Blue Mistflowers

This plant is native to areas with cold winters and is therefore designed to overwinter in freezing temperatures. To help the plant do so with vigor, you may wish to prune away all the foliage in the fall to ensure a clean area for the plant to reemerge in the spring. Placing a layer of mulch or leaves over the soil will help insulate the roots during the cold season.