Ageratum Care Tips: How to Grow Ageratum Plants

Ageratum (Ageratum houstonianum) is a flowering annual native to Guatemala, Belize, and parts of Mexico. Ageratum plants are prized for their flowers’ blue color, though they also come in white, pink, lavender, and red varieties. They’re in the Asteraceae family, along with zinnias, marigolds, and asters. As a result of their color and their playful, fluffy flowers, ageratum is also known as floss flower, blue horizon, and blue mink.

Ageratum is an annual plant, meaning that its life cycle lasts one growing season. It therefore needs to be replanted every year. Ageratum is a low-maintenance plant capable of thriving in a range of hardiness zones, climates, and soil conditions, making it an excellent bedding plant and a good candidate for rock gardens. It’s also especially attractive to pollinators while also being largely deer-resistant.

There are many types and cultivars of ageratum that come in a variety of heights and colors. Some of the more popular varieties to consider for your garden are:

1. 1. Hawaii White and Hawaii Blue: The Hawaii Blue variant is the more popular of the two and has royal blue flowers; Hawaii White blooms white.
2. 2. Blue Danube: The Blue Danube variety is low-growing and sports blue or purple flowers.
3. 3. Artist Purple: The Artist range of ageratum flowers comes in several colors and is notable because the flowers will continue to grow over dead blooms, meaning you won’t need to deadhead them as frequently.

Ageratum can be grown from seeds or plant starts widely available at garden centers. Here are some tips to get you started.

1. 1. Start seeds. If you’re planting ageratum from seed, it’s best to start seeds indoors six to eight weeks before the last frost, as these plants are frost-sensitive. The seeds need light to germinate, there is no need to cover them with potting soil. Place seed trays in a sunny window or use a grow light. (You can skip this step if buying starts from a nursery.)
2. 2. Transplant seedlings. When all danger of frost has passed, you can transplant ageratum seedlings outdoors. Be sure to harden them off before planting them in an area with well-draining soil and full sun to partial shade.
3. 3. Harvest flowers. You should see blooms about eighty days after transplant. Harvest blooms when they are almost but not quite fully open, and enjoy the cut flowers in bouquets.

Ageratum flowers are generally agreeable but require some special touches to really shine.

1. 1. Fertilize regularly. Ageratum plants respond well to regular feeding with a slow-release fertilizer or liquid fish emulsion.
2. 2. Keep the soil moist. Ageratum prefers moist soil, which can be achieved by regular watering and proper mulching. Make sure not to overwater, as weakened plants can be more susceptible to pests like aphids, whiteflies, and spider mites. Be careful not to over-mulch, as too little air circulation can lead to powdery mildew.
3. 3. Plant away from pets and children. Every part of the ageratum plant is poisonous to humans and animals, so grow them in an area safe from pets and children.
4. 4. Research invasiveness. Ageratum plants are considered invasive outside of their natural habitat. Their seeds can spread in the wind, taking over natural habitats. Before planting ageratum, research whether the plant is considered invasive in your area, and consider native alternatives.
5. 5. Watch the leaves. Ageratum often develop yellow spots when they require fertilization or gray spots when they are being preyed upon by pests.

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