German Primrose: A Fresh, New Look

November 4, 2003 - 13:13

University of Alaska-Fairbanks research shows new and successful developments in this crop.

Primula obconica font-style:normal'>, sometimes referred to as German primrose has soft,
pastel-colored flowers in shades of white, pink, orange, purple or lilac. This
primrose is attractive as a flowering potted plant or mixed with other plants
in color bowls or containers. German primrose cannot withstand frost but does
well outdoors during periods of moderate temperatures. The leaves are up to 6
inches long on 2- to 4-inch-long stems or petioles. Flowers appear in loose
upright umbels or clusters on an extended main flower stalk or peduncle (6-7 inches
long).

Cultivar Development

The use and production of German primrose have been limited
because leaves of some cultivars produce an allergen called primin. After years
of breeding work, primin-free selections are now available. The first
primin-free cultivars were introduced in 1990 under the names Freedom and
Beauty. Some individuals still responded with a skin rash to these cultivars
despite the claims of no allergen content. In 1995, the Libre series (Goldsmith
Seeds) was released as true primin-free selections of the German primrose. The
Libre series grows to heights of 8-10 inches, is suitable for 4- to 6-inch
containers and comes in several flower colors including White, Pink, Salmon,
Red and Blue. Additional primin-free cultivars in the Twilly Touch Me series
(Schoneveld Twello) were released in 2000. Sensitive individuals when exposed
directly to the earlier cultivars responded with a skin rash or in some cases
severe dermatitis. The less attractive common name poison primrose probably
stems from these problems with potential allergies.

Current Recommendations

As the risk for skin rash has dwindled with newer cultivars,
the interest and production of German primrose have increased. Propagation is
with seeds, and the germination process requires 10 days to two weeks at
65-68° F. Following germination, the temperature can continue at 65-68°
F with transplanting 6-8 weeks later. The expected time from production to
marketing varies from 4-6 months, depending on conditions and cultivar.

German primrose is considered day neutral, and no specific
day length is recommended for promoting flowering. Contrary to the response of
English primrose (Primula vulgaris) and polyanthus (Primula X polyantha),
reducing the temperature to approximately 40° F does not promote German
primrose flower formation. Plant quality, flower color and size however,
improve in the German primrose at temperatures somewhat lower than 65° F
during the final stages of development.

Conditions for the Study

Information and recommendations for efficient production of
German primrose are rather limited. A study was therefore initiated to
determine flowering in response to day length at two temperatures for the
cultivar selection 'Libre Light Salmon'. The seed germinated at 68° F and
approximately 500 foot-candles during long days of 16 hours. Four weeks later,
seedlings were transplanted into 4-inch pots filled with Premier Pro-Mix BX
(Premier Horticulture), the temperature was maintained at 64-72° F and
irradiance increased to approximately 875 foot-candles for 16 hours each day.

Three weeks after transplanting, when the plants had five or
six expanded leaves, the study was initiated. Plants were grown at 60 or
64-72° F and days with eight or 16 hours of light. To properly maintain the
short eight-hour days, black cloth was pulled over the plants manually at 4
p.m. and retracted at 8 a.m. to avoid interference of adjacent lighted
greenhouse areas and outside lights. Irradiance was 10 mol·day-1m-2
independent of day length with approximately 875 foot-candles for 16 hours or
1,750 foot-candles for eight hours from high-pressure sodium lamps.

This study was conducted during the winter. The influence of
natural light was therefore limited due to the short days and low sun angles.
Horizontal airflow fans were supplemented with fans underneath benches to
ensure proper air circulation and consistent temperatures around the plants
without compromising desired day length conditions. As the plants developed,
flower bud appearance (0.08-inch large flower buds) and first open flowers were
noted and recorded. The study was terminated 146 days from seeding or 97 days
from initiating the experimental conditions.

Results and findings

Time for developing flower buds and reaching flowering
varied for the Libre Light Salmon plants grown at the eight-hour short days and
Á those grown at long days of 16 hours (see Figure 1, page 70).
Temperature also affected floral and overall rate of development. Flower buds
appeared 10 days earlier at short days and 60° F than at 68° F. At long
days, on the other hand, flower buds appeared at a similar time independent of
temperature. The average number of days to flower buds was 38 under long days.

The development of buds into flowers responded strongly to
the temperature and day length conditions. Flowering under long days was more
than a week faster at the higher temperature than 60° F. At short days, the
development of buds into flowers slowed or was even halted. Flowering occurred
on average after 82 short days at 60° F and was delayed compared to long
days with nine or 10 days. No open flowers were observed within the 14 weeks of
short days and 68° F in this study.

Conclusions

Production conditions with long
days were most favorable for the development of German primrose in this study.
At the recommended production temperatures of 65-68° F, long days appear a
requirement for efficient crop development. For rate of development, there was
no advantage of maintaining 68° F compared to 60° F during early development
prior to flower bud appearance. These results suggest lower temperatures
followed by 65-68° F will result in the quickest flowering. Independent of
temperature conditions, long days are likely to produce a faster and more uniform, high-quality crop of German primrose than short-day conditions.

About The Author

Meriam Karlsson is a professor and Jeff Werner is a research associate at the University of Alaska Fairbanks. They may be reached by phone at (907) 474-7005 or E-mail at ffmgk@uaf.edu.

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