Methods

Three varieties of cut flower marigolds were selected for the study, ‘Bindi Orange’, ‘Bindi Yellow’, and ‘White Swan’. ‘Bindi Orange’ and ‘Bindi Yellow’ seeds were obtained from GeoSeed. ‘White Swan’ seeds were obtained from AmeriSeed Inc. All seeds were planted in a greenhouse on March 5, 2021. The seedlings were then transplanted into fields in three locations. Two Mississippi locations and one Louisiana location - the Louisiana State University Botanical Gardens in Baton Rouge, Louisiana were selected. The Louisiana field was fertilized with 13-13-13 at a rate of 500lbs per acre. Transplants were planted in double drills on 48-inch-wide rows. Rows were outfitted with black plastic mulch and a single tube of drip irrigation with emitters at 12-inch spacings. The Louisiana location was transplanted on April 23, 2021. Each variety by treatment was replicated in four plots that were 10-foot in length with 20 plants per plot. The treatments were pinched and non-pinched plots. Therefore, each variety by treatment was represented by 80 individual plants. All plants were tied using the Florida weave method with tomato twine on May 7, 2021. Rain data was collected throughout the trial at the LSU Botanical Gardens.

The ‘White Swan’ variety was taller than the ‘Bindi Orange’ and ‘Bindi Yellow’ varieties at planting. Therefore, the ‘White Swan’ plants were pinched on May 7, 2021. ‘Bindi Orange’ plots and ‘Bindi Yellow’ plots were pinched later in the weeks of May 17 and May 24, 2021. The terminal growing point of plants were pinched exactly 12 inches above the plastic mulch. After pinching, all plots (pinched and not pinched) were fertigated with 10 lbs. of actual N per acre alternating calcium nitrate and potassium nitrate weekly until harvest.

Harvest began in early June and continued through July 2021. Plants were harvested when at least one flower on the stem reached the full open stage. ‘White Swan’ grew the fastest and therefore was harvested earlier than both ‘Bindi Orange’ and ‘Bindi Yellow’ plants. Five plants per plot were sampled for data collection. Data was collected by cutting the plant at mulch or ground level. Individual stems were removed from the plant. The total number of stems per plant were counted. Then, each stem was categorized into marketable and unmarketable classifications. Stems were considered marketable if they were at least 12 inches in length and had at least one full open bloom. The fully open bloom also had to be uniform in shape and free from insect and disease damage. Stem length, number of blooms, and width of each bloom were collected from every harvested plant and stem. Plants were inspected weekly for signs of insect and disease damage. Horticulture soap was applied to all marigold plants twice in late May to combat mite damage. Additional plants were collected from each plot for a separate vase life trial. The vase life trial had no formal ratings, but photos were collected on day of harvest, day 3 and day 7. Data not shown for this portion of the study.

Results

Researchers in this field experiment were expecting slightly different results. As shown in Figures 1-4, there was not a great difference in number of stems per plant, average length of stems, flower size or number of flowers per stem when comparing pinched and not pinched (control) plots within varieties. As expected, there were some differences between varieties. ‘White Swan’ grew more stems per plant than both ‘Orange Bindi’ and ‘Yellow Bindi’ (Figure 1). Stem length was also slightly longer in ‘White Swan’ as compared to the Bindi varieties (Figure 2). Although data was not collected on stem diameter, the researchers did note that the ‘White Swan’ stems were not as sturdy as the Bindi varieties. The ‘White Swan’ stems appeared to fall over in the field and rely on the trellis as compared to ‘Orange Bindi’ and ‘Yellow Bindi’.

Average flower size ranged from 2.2 inches in diameter to 2.9 inches in diameter on average between the pinched and control treatments of the 3 selected varieties. The ‘White Swan’ variety had smaller flowers averaging 2.2 and 2.3 inches in diameter than the Bindi varieties which were closer to 3 inches in diameter (Figure 3). ‘Orange Bindi’ averaged almost two open flowers per stem (one fully open flower and other flowers with at least some color from petals showing), whereas ‘White Swan’ and ‘Yellow Bindi’ both averaged closer to a flower and a half open per stem (Figure 4).

‘Yellow Bindi’ and ‘Orange Bindi’ flowers were outstanding. They appeared bright yellow and bright orange in color. ‘White Swan’ flowers appeared pale yellow when they first started to open and would turn to a creamy white color once fully open. During rain periods, ‘White Swan’ flowers did not hold up. The petals quickly turned brown after heavy rain. The ‘Orange Bindi’ and ‘Yellow Bindi’ flowers remained vibrant in the field even after rains. While the ‘White Swan’ variety was quick to grow, it also had a very short field life in south Louisiana. Harvest could have easily continued for Orange and Yellow Bindi flowers throughout August and into September in this trial. A florist would have a hard time accepting any of the flowers from the ‘White Swan’ variety harvested late July through August, especially in rainy years. Rainfall was heavy during this trial. Rain data was collected each day during the trial; 21.41 inches, 7.6 inches and 7.83 inches were collected in the months of May, June, and July 2021 respectively.

Conclusions

Based on this preliminary trial, we would recommend Louisiana cut flower growers include ‘Bindi Orange’ and ‘Bindi Yellow’ cut flowers on their farms for large showy intensely colored blooms. The plants were relatively pest and disease free. Even in the rainy 2021 season, we did not have to apply many insecticides to achieve florist perfect flowers. Horticulture soap was applied twice for a small amount of mite damage. Fungicides were not applied during this trial. ‘Bindi Yellow’ and ‘Bindi Orange’ blooms would be nice additions to cosmos and zinnia bouquets for a larger showy flower to accent smaller blooming plants. Additionally, the ‘Bindi Yellow’ blooms are perfect for LSU fans needing decoration for football watching parties and tailgates in true Tiger colors. No conclusive benefits were seen from pinching plants. Therefore, based on this preliminary trial, we would not recommend growers pinch plants, as doing so is an added component of labor without significant results.

Figure 1. Average number of stems per plant in the Louisiana Marigold cut flower trial.

Figure 2. Average Stem length (inches) from Plants grown in the Louisiana Marigold Cut flower trial.

Figure 3. Average flower diameter size (inches) from plants grown in the Louisiana marigold cut flower trial.

Figure 4. Average number of flowers per stem, from plants grown in the Louisiana Marigold cut flower trial.