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Manipulating Light to Improve Quality of Cut Flowers

Floriculture Michigan State University logo

Producers are seeking information on how to schedule flowering of new and current cut flower varieties for year-round production. With this information, they will be able to successfully inhibit or induce flowering to schedule crops for specific market dates, increase yield, grow consistent and high-quality cut flowers year-round, and subsequently satisfy consumer demand for locally produced stems. In addition to this research, funded by the American Floral Endowment, Dr. Roberto Lopez recently hosted a Grow Pro Webinar covering Cut Flower Production in the Northern US.

Once completed, this research will provide growers with well-defined recommendations for vegetative and reproductive growth to increase cut flower production efficiency and profitability. Specifically, we are quantifying how several new and commercially important cut flower varieties respond to daylength and/or vernalization temperature and duration to ultimately determine how these environmental parameters should be managed to hasten flower initiation and induction without negatively impacting stem quality and yield. This information is especially crucial for cut flower growers located in northern latitudes as they transition to year-round greenhouse production.  

Bluebeard (Caryopteris ×clandonensis) and Billy button (Pycnosorus globosus) are both crops that have been recently introduced as cut flowers, however, there is very little production and flower induction information available. These crops have the potential to be high-value fillers as their morphology complements and is distinct from traditional cut flowers. Our research with bluebeard and Billy button has determined the critical daylengths for floral initiation. Additionally, we have determined the daylength(s) that will hasten flower induction and lead to a consistent supply of high-quality stems. 

Persian Buttercup (Ranunculus asiaticus) is a staple and high-value cut flower; however, few growers are able to schedule this cool season crop to meet specific market dates. As this crop becomes increasingly popular with consumers, growers are looking to hasten flowering, and increase yield and stem consistency between successive plantings. Although field and high tunnel ranunculus production research has been previously conducted, there are contradictions and gaps in knowledge regarding environmental triggers for flower initiation and induction and vegetative growth prior to induction to increase yield and stem length. In addition to photoperiod, this research has also determined how vernalization temperature and duration of rehydrated ranunculus corms after transplant hastens flowering and stem quality. 

Summary of research conducted:

Figure 1. Caryopteris ‘Pagoda Logoon’ were grown under a 9-, 10-, 11-, 12-, 13-, 14-,16-h photoperiod or a 4-h night interruption (NI). Photograph was taken 5 weeks after plants were placed under treatments.

1. Caryopteris and Pycnosorus

The first replication of our bluebeard and Billy button photoperiod research has been completed.

Cuttings of Bluebeard ‘Pagoda Lagoon’ and Billy button PaintballTM ‘Globe’ were received and rooted. The rooted young plants were subsequently transplanted into bulb crates filled with a peat and perlite-based substrate. Crates were placed under eight different lighting treatments, including a 9-, 10-, 11-, 12-, 13-, 14-, 16h photoperiod, or a 4-h night interruption (NI) from 10 pm to 2 am.  

Plants were monitored daily for the presence of visible buds (VB) and open flowers (OF). The number of nodes below the VB and the date was recorded. Stems were also monitored until they reached a marketable stage when they were harvested. Stem length, caliper, and inflorescence diameter were measured, and the number of branches was recorded.  

We determined that flowering of bluebeard was hastened under a 9- and 10-h photoperiod (Figure 1). However, these stems were not considered marketable as the majority were shorter than 40 cm in length and internodes between flower buds were very short. Plants grown under 11-, 12-, 13-, and 14-h photoperiods produced marketable stems >40 cm. While plants under the 16-h photoperiod and 4-h NI initiated flower buds, buds did not ever fully develop over the duration of the study (Figure 1). For Billy button, flower bud initiation and induction were similar across all photoperiods (Figure 2). Billy button stem length was greatest under 11-, 12-, 13-, and 14-h photoperiods. Additionally, plants grown under the shorter daylengths exhibited more branching.  

This research is beneficial to growers interested in introducing new cut flowers into their product line. We are classifying bluebeard as a day-neutral plant for flower induction and a short-day plant for flower development as only plants under ≤14-h flowered and Billy button as a day neutral plant for both induction and initiation.

Figure 2. Pycnosorus PaintballTM ‘Globe’ were grown under a 9-, 10-, 11-, 12-, 13-, 14-, 16-h photoperiod or a 4-h night interruption (NI). Photograph was taken 8 weeks after plants were placed under treatments.

2. Ranunculus 

The first replication of our ranunculus photoperiod and vernalization study has been recently completed. Ranunculus corms ‘La Belle White’, ‘Tecolote Salmon’, and ‘Butterfly Artemis’ were received and rehydrated in running 20 °C (68 °F) water for 8 h before being planted into trays. The trays were then placed in a 4.5 °C (40 °F) cooler for a 4-week pre-sprout period. Trays were then placed in vernalization treatments of 3.5, 5.0, or 7.5 °C (38, 41, or 45.5 °F) for 0, 2 or 3 weeks. Sprouted corms were then transplanted into crates and placed under 12-h, 14-h, or 16-h photoperiods. 

Ranunculus plants were monitored for VB and OF, when the stem was harvested and considered marketable. Stem length and caliper were measured and the number of lateral branches with flower buds was recorded. The total number of marketable stems per plant was also recorded. It was observed that time to OF was hastened under the 16-h photoperiod, while those under the 12-h photoperiod were delayed. However, plants grown under the 12-h photoperiod were larger and more vegetative than plants grown under the 14- and 16-h photoperiods. The larger plants produced flowers with generally more and longer stems. We are currently analyzing our data to determine the influence of vernalization duration and temperature.

This information is valuable for ranunculus growers because it will provide recommendations for vernalization temperature and duration and photoperiod for flower initiation and induction. Growers will directly benefit from optimized production and an increased yield. 

Objectives for the upcoming year: 

  1. To replicate the blue beard, Billy button, and ranunculus photoperiod studies and include additional series and cultivars to ensure that different series and varieties respond similarly.
  2. To quantify if vernalized ranunculus plants should be grown under a 9-h short-day prior to inductive long-days to encourage vegetative growth and the production of more and longer stems.
  3. To quantify the minimum number of short-days required to hasten flowering of dahlia grown under long-day conditions.

Significance to Industry

This research will provide information for growers seeking to schedule cut flowers that either have a short-day (SD) or long-day (LD) flowering response for year-round production. It will also emphasize the importance and utility of supplemental and photoperiodic lighting for the cultivation of high-quality cut flowers during the winter and early spring. With this information readily available, growers will be able to successfully schedule and grow consistent and high-quality new and current cut flowers year-round, and subsequently satisfy consumer demand.

By Jessica Brown and Dr. Roberto Lopez, Department of Horticulture, Michigan State University