Common Name: Dahlia

General Information

Dahlia pinnata is a herbaceous perennial plant growing from a tuberous rootstock; it produces a clump of usually unbranched stems around 100 - 150cm tall, occasionally reaching 180cm[, ].
The tuberous roots were commonly used for food and medicine in pre-Columbian Mexico, and are still eaten to a limited extent in the present day[]. Gathered from the wild, they are sometimes sold in local markets[]. This species is a parent of the cultivated Dahlias that are so commonly grown as ornamentals.

Known Hazards

We have no specific information for this species, but the leaves and tubers of several Dahlia species are known to contain phototoxic polyacetylene compounds that can cause skin irritation following repeated handling of the tubers and contact with leaves and light[].

Botanical References

, ,

Range

Southern N. America - Mexico. Naturalised in much of Central America

Habitat

Rich damp oak and pine woods, sandy meadows at elevations up to 1,800 metres[, , ]. Rocky slopes; at elevations from 2,100 - 3,000 metres[].

Properties

Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Perennial
Height	1.00 m
Pollinators	Insects
Self-fertile	No
Cultivation Status	Ornamental, Wild

Cultivation Details

Most Dahlia species in Mexico grow at moderate to higher elevations, typically above 2,100 metres in southern Mexico, where there can be rapid changes in temperature, but no frosts[]. The dahlia’s home area in the volcanic highlands of southern Mexico is hot and dry during the winter months but the rainy season during summer is characterized by afternoon thunderstorms. Also, dahlias are adapted to grow while being bathed in dew from the low hanging clouds[]. The top growth of Dahlia pinnata is very frost-tender, though the tubers are somewhat hardier and can tolerate temperatures down to about -5°c[].
An easily grown plant so long as the soil does not dry out[]. It requires a deep rich soil and a sunny position[], disliking shade[]. Dahlia species in the wild are generally found on well-drained hillsides, rough banks and cliffs. The soil is typically a soft, porous and sandy loam with a gravelly subsoil which is often volcanic and mildly acidic[].
Dahlia tubers are worth some experimentation as a root crop either for food or for sugar production since their root sugar content is quite respectable even without artificial selection. For example, up to 15 sweet potato-sized tubers, containing as much as 13% fruit sugar, can be produced by a single plant in one season under optimum conditions. This high sugar content, even among wild dahlias, compares favorably with sugar beets, even though sugar beets have been scientifically selected so that their sugar content has been increased from 7% to 20%. Such scientific breeding could lead to a similar increase in the sugar content of dahlias if they become recognized as a worthwhile agricultural plant[].

Edible Uses

The flower petals are used in salads[, ].

Root - cooked and used as a vegetable[]. A bitter flavour[]. Inedible according to another report[]. A sweet extract of the tuber, called 'dacopa', is used as a beverage or as a flavouring. It is mixed with hot or cold water and sprinkled on ice cream. Its naturally sweet mellow taste is said to combine the characteristics of coffee, tea and chocolate[]. The root is rich in the starch inulin. Whilst not absorbed by the body, this starch can be converted into fructose, a sweetening substance suitable for diabetics to use[, , , ]
There are contradictory reports regarding the edibility of Dahlia tubers, ranging from sweet and juicy to extremely bitter, hot and dry tasting and virtually inedible. This could be due to the time of year the tubers are harvested. If gathered at the beginning of the rainy season - after the inulin had been converted by enzymatic action to produce fruit sugar and before the rapid growth of the tall stalk had depleted the tubers of food - then the tubers would, indeed, have been sweet tasting and juicy. In the second case, if the tubers were gathered late in the growing season or at the beginning of the dry season - before the return of the plants’ food and water resources back into the tubers for storage -then the medicinal constituents of the depleted tubers (especially the skin) could have been expected to give a potent and unpleasant taste. In short, dahlia tubers to be eaten raw immediately should be harvested in the spring, and those intended for medicinal use should be gathered later in the summer when the growing season is well advanced but before the start of the dry season and those intended for baking or storage as food should be gathered well after the start of the dry season when the upper parts of the plant have wilted down in the manner of potato stalks and the tubers are full of inulin, which keeps well[].

Medicinal

A valuable and much needed drug was extracted from dahlia roots during the first world war[]. No more information was given in the report[].

The plant (probably the tubers) was used as a diuretic and diaphoretic, it was used to treat colic, tuberculosis, and flatulence. The roots are said to be hot and dry in the third degree, aromatic, bitter and sour to the taste. Taken internally, it cures flatulence, mitigates the pain of the mid-section, provokes urine, brings out sweat, drives out chill, strengthens the weak stomach against chill, combats colic and opens the obstructed tubule, whilst applied externally, it dissolves tumors[]

Other Uses

Orange, yellow and gold dyes are obtained from the flowers and seed heads[, ].

Extracts of both the leaves and the seeds are used as ingredients in commercial cosmetic preparations as emollients and skin conditioners[].

Propagation

Seed - usually germinates in 1 - 3 weeks at 20°c[]. When they are large enough to handle, prick the seedlings out into individual pots and grow them on until large enough to plant out.
Cuttings of young shoots as new growth begins.
Division of the tubers when dormant. Each portion should have a growing point[].

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