Search This Site:

Ageratum Houstonianum. The Blue Floss Flower. A Gardener's Delight.

Ageratum Houstonianum In A Garden Bed with Begonias and Marigolds.

The Ageratum houstonianum or Floss Flower as it is more commonly known, belongs to the Asteraceae family - the same very special family to which the Daisies, Asters, Gerberas, Chrysanthemums and so many others all belong. It is a Native plant of Mexico.  There are many types of Ageratum, but Ageratum houstonianum is the most commonly used in both home and display gardens of all kinds.

This family is special because of its secret: its unique and astounding method of reproducing. Its botanical name is Ageratum houstonianum, coming from the famous 18th Century Botanist, William Houston. It is native to Central America and Mexico and four types are native to the United States.

The original flowers were blue, but different methods of cultivation and hybridization have given us pinks, white, lavender, purple and even yellow. The yellow is called the Golden Ageratum or Lonas inodora.  The gorgeous fluffy flowers of Ageratum open from tiny buttons all over the seed head, just like the Bottlebrush, Calliandra and other similar flowers. Amazingly, each tiny wisp of fairy floss is a petal. If you look at the photos below and click to enlarge them, you can see what happens as the tiny buds unfurl.

Ageratum Flower Unfurling.

Calliandra Spikes Opening.

Ageratum houstonianum really is a marvellous plant. It has so many pluses and very few minuses.  An amazingly versatile and easy care plant. Not only does it flower from spring right through until late autumn, but it is also relatively disease and bug resistant. A tendency to develop Powdery Mildew seems to be its only downside (see below about how to overcome this). It prefers a cool climate but can easily adapt to a temperate zone. It comes in sizes from about 6" to 30" high and spreads to about 18". So make sure you give it enough room. 

It looks great when there are a lot together, so don't just buy one. It comes in small, medium and large for the back row. It looks great as an edging and bedding plant or as a tallish plant against a wall and makes a perfect container plant. 

'Blue Mink'. Nice and Straggly. 

It loves water but it is very forgiving if you forget occasionally. It springs back easily if it's been a bit dry. However, it will not tolerate too much drying out which will cause it to wilt. Two or three times a week for this plant, especially in summer. The only precaution to take  is to water around the roots, not on the foliage or flowers. This will help get rid of any powdery mildew problems.

Most pictures you see of Floss Flowers show them crammed into bedding gardens. Whilst this looks good, it means they can't get sufficient air to circulate around their stems, which is a another major cause of powdery mildew. So a little give and take and planning for the future is necessary here. Close, but not too close is the best way to go. 

Beautiful Powder Puff Blue Mink.

If you are handling this plant a lot, then wash your hands afterwards. In some people it may cause skin problems. As for animals, it is highly toxic to the liver if eaten. This also makes it deer resistant. But it's perfectly safe for Butterflies and they certainly love it. So do the Hummingbirds.

When planting Ageratum, give the soil some compost mulch and that should be all it needs. If you do want to fertilize it further down the track, a slow release form is best. This plant definitely deserves the best, but avoid the tendency to kill it with kindness. It doesn't need that much attention. 

To squeeze out every last bloom and extend the flowering season, always deadhead the flowers when they've finished.

On top of all its other qualities, Ageratum will also grow in full sun and part shade. And the flowers are great to cut and bring into the house, although they are not perfumed. If you can find the Award Winning Ageratum called 'Artist Blue', it would be the loveliest of all the Floss Flowers for your garden. It is a deep blue and looks absolutely stunning. Award winners are the most reliable of all plants.

Most of the Ageratums form a compact mound shape (they remind me of Broccoli), but the tall ones are more elegant and leggy.

Home. Return from Ageratum Houstonianum to Annual Plants.