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CALENDULA CULTURE
by Nancy Garrison, Horticultural Advisor, Santa Clara County
adapted from Lyle Pyeatt's research in 1983
Few annual flowers are as easy to grow as calendulas; they are excellent for flower bed plantings and also grow quite well in containers. Calendulas make good long lasting cut flowers as well. A member of the daisy family, the flowers resemble the marigold and measure from two and one half to four and one half inches in diameter; so they are sometimes called pot marigold. The flower colors range from orange, apricot and bright yellow, to lemon, cream and nearly white. Maximum height in standard cultivars is about twenty four inches, while dwarf cultivars grow to only twelve inches. Plants are somewhat branching, with leaves that are long and narrow, slightly sticky and aromatic.
Current horticultural literature describes calendula (C. officinalis) as a cool season annual. The season of calendula commercial availability seems to reinforce the notion that it must be grown during the cool season in most of California. However, some seed companies offer cultivars described as heat resistant.
Calendulas should be grown in full sun and in moderately fertile soil. When they are grown during the cool season the flowers are apt to be larger, the stems somewhat shorter and the peak flowering period longer than if grown during a warm season planting. One can expect summer plantings in San Jose to be successful in summers that are not excessively hot.
Seeds sown in August should bloom well before Christmas and will provide color all winter. Fall planted seeds will provide flowers in the spring. For cut flower use, pick the blooms in bud or when they are just beginning to open. Fully opened flowers will wilt rapidly in the vase.
The only universal problem with calendulas in the San Jose area is mildew. Research has shown some of the calendula cultivars to have enough mildew resistance to warrant chemical sprays unnecessary, especially in the varieties 'Green Crown' and Orange King'. Optimum conditions for development of the causal fungus are frequently present during the warm season.
In order to observe warm season performance, a field planting of twenty one cultivars of calendula was made on a quarter acre plot of ground at the University of California Deciduous Fruit Field Station on Winchester Boulevard in San Jose. Seeds were planted in the greenhouse April 12, 1983, in two inch pots and field planted on May 24. Plants were set twelve inches apart within rows, and the rows spaced forty inches apart. Initially the plants were sprinkler irrigated, and when fully established, furrow irrigation was used. Plants in this test were allowed to grow naturally without any attempt to production two months after planting in the field. During this study temperatures peaked in July with fifteen days over eighty degrees, one day in the ninety's and three days over one hundred.
A second study was performed on calendulas to observe cool season performance. Twenty three varieties were seeded August 24, 1983, transplanted to cell packs September 7 and planted in the field September 22. Again, plants were sprinkler irrigated and then furrow irrigated. Stem height was not controlled and all cultivars were allowed to reach peak flower production. An alphabetical listing of the varieties appears at the end along with the retail seed sources from which they were obtained.
At the end of the studies all cultivars were rated for resistance to mildew, cut stem length, and plant height. The conclusions follow for both the warm and the cool season studies.
A rating for occurrence of powdery mildew (See Table 1) at the time of peak flowering late in July was determined for each cultivar. The following five cultivars proved most resistant to mildew: Orange King, Chrysantha Sunshine, Golden Beauty, Dwarf Orange and Balls Orange. These cultivars all had a subjective mildew rating of four or lower, with Chrysantha Sunshine, Dwarf Orange and Orange King showing very little mildew at all (a rating of one or lower). The appearance of cultivars rated above five in the 0-10 index would likely be a problem whether grown for cut flowers or in a landscape situation. The above observations indicate that powdery mildew disease poses a greater problem than temperature during summer for the commercial production of calendula in some major flower and plant production areas of California such as the San Jose area.
Most cultivars grown during the warm season were quite uniform for height with the only exceptions being Balls Orange, C. officinalis, Geisha Girl, Pacific Beauty Lemon and Chrysantha Sunshine. This variability in height should not prevent their use as bedding plants in an informal setting or as cut flowers. Cut stem length measurements for all varieties ranged from six to twenty inches, with most stem lengths measuring between twelve and sixteen inches. All varieties flowered abundantly during the summer.
Powdery mildew posed a much greater problem during the cool season than the summer (See Table 2). By the end of the growing season all of the varieties were more than half covered with mildew. Height was uniform in the majority of the varieties and ranged form nine inches to twenty three inches. Six cultivars were variable in Height, and are listed as follows: Apricot Orange, Art Shades, Balls Orange, C. officinalis, Geisha Girl and Lemon Beauty. Many varieties flowered abundantly, but some did poorly or did not bloom at all. Dwarf Golden Gem, Fiesta Gitana, Goldfinch (grew generally poorly), Apricot Shades, Art Shades, Lemon Coronet, and Mandarin bloomed poorly or not at all.
When a field day was held at the Field Station on January 17, 1984, the public rated their favorite cultivars of calendula as follows. The most popular by far was the Geisha Girl, receiving 8 of 31 votes cast. Yashima was the next highest scorer and Dwarf Orange, Green Crown and Persimmon Beauty tied for third place.
Variety:
Apricot Sherbet (P)
Art Shades (H)
Baby Orange (TM)
Balls Orange (H)
Calendula Officinalis (TM)
Chrysantha 'Sunshine' (H)
Dwarf Golden Gem (TM)
Early Nakayasu (H)
Fiesta Gitana (S)
Goldfinch (H)
Green Crown (TM) Lemon Coronet (HB)
Mandarin (TM)
Orange King (H)
Pacific Beauty Series
Apricot Beauty (S)
Cream Beauty (S)
Flame Beauty (S)
Golden Beauty (S)
Lemon Beauty (S)
Persimmon Beauty (S)
Yashima (H)
Seed Source Addresses:
TABLE 1. Comparison of twenty one calendula cultivars grown during the warm season
Deciduous fruit field station.
| CULTIVAR | COLOR | MILDEW INDEX*** | HEIGHT (inches) | CUT STEM LENGTH (in) |
|---|---|---|---|---|
| Apricot Orange | apricot | 9.5 | 15 | 8 - 12 |
| Art Shades | gold, orange | 1 - 8** | 25 | 12 - 20 |
| Baby Orange | orange | 4 | 15 | 8 - 12 |
| Balls Orange | orange | 4 | 15 - 22 | 12 - 16 |
| C. officinalis | orange, gold, cream | 0 - 9** | 16 - 28 | 12 - 18 |
| Chrysantha 'Sunshine' | gold | 1 | 15 - 20 | 8 - 15 |
| Dwarf Golden Gem | orange | 0.5 | 15 | 1 - 12 |
| Fiesta Gitana | cream-yellow, orange | 5 - 9** | 12 | 6 - 8 |
| Geisha Girl | dark orange | 2 | 16 - 22 | 10 - 15 |
| Goldfinch | golden orange | 1 | 23 | 12 - 18 |
| Green Crown | gold | 0 | 23 | 12 - 18 |
| Lemon Coronet | yellow | 9 | 19 | 10 - 14 |
| Mandarin* | cream, apricot | 10 | 17 | 8 - 12 |
| Orange King | orange | 1 | 36 | 12 - 18 |
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Pacific Beauty
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* Colors observed in test planting do not agree with seed company description.
**Varies from plant to plant.
***Powdery mildew index (a qualitative estimate of visual appearance) from 0 to 10.
0 = No powdery mildew disease at full bloom stage.
10 = All leaf and stem surfaces infected at full bloom stage.
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