Floss Flower: How To Care For Ageratum Houstonianum

Ageratum houstonianum – the botanical name for the Floss flower, an annual flowering plant native to Mexico. The Ageratum flower produces fuzzy, tufted flowers in rounded, dense flower heads adding a desirable blue flower color to the garden, even in partial shade. They can grow from 12 to 39 inches tall.

A popular option for edging borders, window flower boxes, and flower beds. It is one of the few annual plants tolerant of light shade. Ageratum blooms from late spring through summer and all above qualities make this species of flowering plants a fine choice for outdoor containers.


The Ageratum is also considered one of the best mosquito repellent plants. If you desire a splash of pink, white, or blue in your garden, replace the plants each year.

Step 1: Preparation On Ageratum Care

Start floss flower seeds indoors about 6 to 8 weeks before the last frost. Take your young plants outside after all the danger of frost passes.

Plant these annuals under 12 inches in a sunny to lightly shaded area of your garden in moist and well-drained soil. Ageratum is not particularly choosy about soil conditions but does not do well in soggy conditions.

To the planting location, add 4″ to 6″ inches of organic compost incorporating it into the soil using a garden tiller. The compost helps to improve the soil’s fertility, an important factor for the health and Ageratum growth.

Step 2: Planting 

Space plants 8″ to 10″ inches apart. Dig the planting holes of similar width to the root balls with depths similar to the one the plants were growing in prior to transplanting.

Place the young plants into the holes and cover the root balls completely with soil and water thoroughly to compact the soil.

Step 3: Mulching

Around the base of your plants apply a 2″-inch layer of mulch to ensure the soil does not dry out. For best results, use grass clippings, organic compost, or bark mulch.

Be sure to refresh the mulch layer as it decomposes to always ensure you maintain it not less than 2″ inches.

Step 4: Watering

Blue Ageratums does not do well if conditions are too dry and they will wilt quickly if this is the case. Since the plant prefers warmth over cold, some people suggest watering the plant using slightly warm water as opposed to cold.

This is particularly important when the plants are young since warm water seems to accelerate the growth of the plant.

To ensure the soil remains consistently moist throughout the summer and spring, it is important to water floss flowers regularly.

Ageratum flowers require about 2.5″ inches of water a week. For daily irrigation use a soaker or use a sprinkler for watering twice weekly. Reduce the amount of water you give to the plant if you receive more than 1 inch of rainfall in a particular week.

Step 5: Fertilizer Application

Feed your ageratum plant once a month using water-soluble liquid blooming plant fertilizer. If necessary you can pull back the mulch around your plants slightly during application.

Follow the instructions provided on the packaging for proper dosage and application.

Step 6: Removing Spent Flowers

Ensure you get rid of spent flowers as they fade to encourage more prolific blooming.

The new blooms of the flossflower form on top of the old ones but you should still pinch off the browned blossoms occasionally to encourage new growth.

Remove the browned blossoms using your fingers and as close to the stem as possible.

Blue Floss Flowers Pests & Problems

When cared for properly, the ageratum flower is generally hardy. However, you need to look out for a few pests.

Deer is the largest-sized pest. Whiteflies can weaken the plant and cause the pointy leaves to yellow.

You can lure away the flies from your plants using an old-fashioned fly trap made by painting a post bright yellow then covering it with a sugar solution, honey, or any other sticky substance.

If you discover severe wilting, yellowing, or dying Agregatum leaves or find any lesions on the stems, it means that your plants have probably succumbed to a bacterial infection.

You need to remove the unhealthy plant to ensure that the infection does not spread.

You may find mold on the flowers and stems or brown spots on the foliage of your plants. They will probably survive the problem through the season.

However, it can be advisable to thin your plants to allow more air flow around the plants. Sunlight also keeps the flowers and leaves drier too thus preventing molds from damaging your plants further.

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