PLANT OF THE WEEK

Dr. T. Ombrello - UCC Biology Department

 

CHRYSANTHEMUM

 

Common names:        Chrysanthemum, Mum

Scientific name      

Dendranthema x grandiflorum     (formerly  Chrysanthemum morifolium)

Explanation of scientific name:       

Dendranthema - from the Greek meaning "tree flower" (Anthemis Tribe)

grandiflorum - large flowered

Chrysanthemum - from the Greek meaning "golden flower"

(Historically, chrysanthemums were primarily yellow flowered.)

morifolium - mulberry leaved (the leaves resemble mulberry leaves)

The chrysanthemum (or "mum" for short), is the traditional flower of fall, having been grown and prized by people for a longer period of time than have most domesticated plants.  The Chinese were growing it 2000 years ago and in Japan, where it is the national flower, its cultivation goes back at least 1000 years.

Hardy garden mums growing on the UCC campus in Cranford, NJ.
A crop of potted Chrysanthemums grown by Plant Science students, in one of Union County College's greenhouses.

Introduced into Holland in 1688, by the 18th century mums were being grown in France and England.  Widespread cultivation in Europe began in the 19th century when nurseries started to specialize in growing varieties developed by hybridization and importation from the Orient.  Their introduction into America is lost in history, but mums were apparently grown here not long after they became popular in Europe.  By the time the Massachusetts Horticultural Society was incorporated in 1829, there were at least 17 varieties recognized in the United States.  Grown as hardy outdoor plants until the mid-1800's, the development of glass greenhouses allowed for the culture of non-hardy mums, too.  They came to be known as florist mums, grown for cut flowers and later as potted plants.  While there are many categories of chrysanthemums today, in our area one is likely to encounter either florist's mums or hardy garden mums.  Mums are so popular that they are grown for sale 12 months of the year; they aren't just for Fall any longer.  We are especially fond of mums in this State.  New Jersey greenhouses grow more potted mums per capita (at least one for every 2.6 people) than any other state.

Mums are easy to grow.  They root readily from cuttings, and large plants can be dug up and divided.  However, in order to grow the high quality plants found in florists and garden centers, a few basic horticultural principles must be followed.

 1.         PINCHINGPinching growing tips

Mums tend to grow tall with few side shoots if left to themselves.  They lose their lower leaves and become top heavy when in bloom and tend to fall over.  Cutting (pinching) off the growing point on each new shoot that is several inches in length will produce a compact, multi-branched plant capable of producing many flowers.  Pinching is done repeatedly on new shoots until the conditions are right for flower development.  Then the growing points are left intact to develop into blooms.

 2.        DAY LENGTH:   

Mums are short day plants, meaning they require long nights (in excess of 11 to 12 hours) in order to induce flower development.  Hardy garden mums in our area grow vegetatively in the spring and summer and bloom in the fall based on day length.  By mid to late summer, the night lengths are long enough to promote flowers.  Some cultivars of mums respond faster than others, and that's why you might see some hardy garden mums in bloom in August, while others wait until October.

Since florist's mums (as cut flowers or in pots) are in demand all year long, day lengths must be regulated in a timely fashion depending on the season.  In order to grow florist's mums to bloom in the winter, newly rooted plants initially must be grown under long-day conditions in order to grow vegetatively.  This is done with artificial lights timed to extend the day length.  When the plants reach sufficient size, the artificial lights are removed, and the naturally short days promote blooming.  For mums to bloom in the summer, the opposite strategy is followed.  Newly rooted cuttings naturally grow vegetatively because the days are long and the nights are short.  When the plants reach sufficient size, the day lengths are artificially shorted (by covering the plants for part of each day with a black cloth) in order to promote blooming.

3.         DISBUDDING:   

Each shoot on a mum usually produces several flowers of relatively small size, often closely pressed against each other distorting the flowers.  In order to produce large, exhibition size mums of perfect form, the plants are disbudded.  As the flower buds appear on each shoot, all but the largest are removed (disbudded).  The remaining single bud on each shoot will develop into a large, perfectly formed flower.

 There are literally thousand of different mums available today, in just about all colors, sizes, and shapes.  If one does not care to grow their own, the mum's low cost allows them to be enjoyed by all who appreciate flowers.