Colin Mills, compiler of the Hortus Camdenensis, died in late November 2012 after a short illness. As he always considered the Hortus his legacy, it is his family's intention to keep the site running in perpetuity. It will not, however, be updated in the near future.

Ageratum houstonianum Mill. var. caeruleum

The wild type is a short-lived perennial, a somewhat untidy plant with blue flowers.  To 60cm.  It is mostly grown as an annual, with most cultivars being compact, mound-forming plants, 15-30cm tall, with numerous small, rounded flower clusters in shades of blue, red and white in summer.  [RHSE, Hortus].

Horticultural & Botanical History

Introduced to Europe in the early nineteenth century.  Johnson’s Dictionary gives a date of 1800 for A. caeruleum and 1822 for A. mexicanumAgeratum mexicanum was raised by Mr. Tate of the Sloane Street nursery from seeds brought from Mexico by Mr. Bullock.  [BM t.2524/1824].  A. mexicanum was recommended as a useful winter greenhouse plant in The Gardeners Chronicle.  [Gard. Chron. 1854]. 

History at Camden Park

Listed in the 1850 and 1857 catalogues [H.3/1850].  Ageratum houstonianum is well established as a weed in parts of Australia and interestingly grows wild throughout the site of John Bidwill’s garden at Tinana.


Ageratum caeruleum Hort. ex Poir. = Ageratum conyzoides L., synonym Eupatorium conyzoides (L.) E.H.L.Krause, a closely related plant.

Published Sep 09, 2009 - 04:53 PM | Last updated Feb 23, 2010 - 01:20 PM

Figured is a spindly shoot topped by an umbel of pale blue flowers.  Curtis's Botanical Magazine t.2524, 1824.

Ageratum houstonianum Mill. var. caeruleum | BM t.2524/1824 | BHL

Family Asteraceae
Region of origin


  • Ageratum caeruleum Hort.
  • Ageratum conyzoides L. var. houstonianum (Mill.) T.R.Sahu
  • Ageratum mexicanum Sw. 
Common Name

Floss flower, Mexican ageratum, Ageratum

Name in the Camden Park Record

Ageratum caeruleum  

Confidence level high