Energy-Efficient Annuals: Dahlia & Osteospermum

Energy-Efficient Annuals: Dahlia & Osteospermum

Producing spring bedding plants in an energy-efficient manner requires information on how crops respond to average daily temperature and daily light integral (DLI) so bedding plants can be more precisely scheduled. At Michigan State University (MSU), we have performed experiments with numerous seed-propagated annuals to quantify how these environmental factors influence flowering time and plant quality. 

In the ninth article of this series, we present crop timing data on dahlia (Dahlia × hybrida) and osteospermum (Osteospermum ecklonis) and then use that information to estimate greenhouse heating costs at different locations, growing temperatures and finish dates.  

Materials & Methods

Seeds of dahlia ‘Figaro Mix’ and osteospermum ‘Passion Mix’ were sown in 288-cell plug trays by C. Raker & Sons and grown in controlled environmental growth chambers at MSU at a constant 68°F (20 °C). Inside the chambers, the photoperiod was 16 hours and the DLI was 9 to 11 mol∙m¯²âˆ™d¯¹. This DLI is typical of that received in greenhouses in early spring in the Northern United States.
 
When plugs were ready for transplant (26 to 30 days after seed sow), they were thinned to one seedling per plug and transplanted into 4-inch (10-cm) pots and grown in greenhouses with constant temperature set points of 58, 63, 68, 73 and 79°F (14, 17, 20, 23 and 26°C). At each temperature, plants were grown under a 16-hour photoperiod with two different DLIs provided by sunlight, a combination of shade curtains and different supplemental lighting intensities from high-pressure sodium lamps. 
 
Dahlia is typically a facultative short-day plant. Although plants flower under long days, flowering is accelerated under short days. In contrast, osteospermum is typically a facultative long-day plant, meaning plants flower faster under long days. 
 
Our experiments were performed twice to obtain average DLIs that ranged from 4 to 19 mol∙m¯²âˆ™d¯¹. To give perspective, a DLI of 4 mol∙m¯²âˆ™d¯¹ is representative of light conditions received by a northern greenhouse on a cloudy day in the winter; a DLI of 19 mol∙m¯²âˆ™d¯¹ is typical for inside a greenhouse on a mid- to late spring day. We recorded the flowering date when each plant had an inflorescence with one whorl of petals fully reflexed. On that date, plant height and number of inflorescences (flower number) were recorded. 
 
Crop timing data were used to develop mathematical models to predict flowering time and plant quality under different temperature and DLI conditions. The Virtual Grower 2.5 software (available free at VirtualGrower.net) was used to estimate the cost to heat a 21,504-square-foot greenhouse (about half an acre) to produce each crop for different finish dates and at different locations in the U.S.

Results

In both dahlia and osteospermum, time to flower decreased as average daily temperature increased from 58 to 73°F. For example, in dahlia grown under a DLI of 10 mol∙m¯²âˆ™d¯¹, time to flower from a 288-cell plug decreased from 60 days at 58°F to 45 days at 73°F (Figure 1). Our crop model predicted the shortest flowering time in this dahlia variety occurs at an average daily temperature of 72°F, and flowering is delayed at warmer temperatures. The crop timing data for dahlia is for plants grown under long days, and flowering may have been accelerated if short days had been provided. Regardless of day length, we anticipate similar temperature trends on crop development rates. 
 
In osteospermum, plants grown under a DLI of 10 mol∙m¯²âˆ™d¯¹ and at 73°F flowered two weeks earlier than plants grown under the same DLI, but at 58°F (Figure 2). To illustrate the effect of temperature on dahlia and osteospermum crop times, we identified dates 288-cell plugs grown under long days would need to be transplanted for two market dates when finished under long days and a DLI of 10 mol∙m¯²âˆ™d¯¹ (Table 1).
 
As the DLI increased, time to flower in both crops decreased. For example, in plants grown at 63°F, increasing the DLI from 5 to 15 mol∙m¯²âˆ™d¯¹ accelerated flowering of dahlia by 15 days and of osteospermum by three weeks. The estimated saturation DLI for the shortest time to flower was 16.4 mol∙m¯²âˆ™d¯¹ for dahlia and 18.8 mol∙m¯²âˆ™d¯¹ for osteospermum. In other words, increasing the DLI above these values did not shorten crop times. 
 
The influence of DLI on flowering time also illustrates the benefit of using supplemental lighting is greatest when the natural DLI is lowest (during the winter and early spring). For example, our models predict osteospermum grown at 68°F would flower 16 days earlier if the DLI was increased from 5 to 10 mol∙m¯²âˆ™d¯¹, and only three days earlier if the DLI was increased from 10 to 15 mol∙m¯²âˆ™d¯¹.
 
In both crops, flower number increased as average daily temperature decreased and as DLI increased. For example, under a DLI of 10 mol∙m¯²âˆ™d¯¹, as average daily temperature decreased from 79 to 58°F, flower number increased twofold in dahlia and sevenfold in osteospermum (Figure 1 and 2). In both crops, plants grown at 79°F and under 4 mol∙m¯²âˆ™d¯¹ developed only four to six inflorescences before flowering, and plant quality was low. 
 
Plant height at flower decreased as DLI increased and as average daily temperature decreased. Dahlia and osteospermum grown cool and under high light (58°F and DLI of 18 mol∙m¯²âˆ™d¯¹) were 9 inches (23 centimeters) shorter than plants grown warm and under low light (73°F and DLI of 4 mol∙m¯²âˆ™d¯¹). 

Heating Costs

We used this crop timing information and Virtual Grower to predict the amount of energy consumed to produce a flowering crop of dahlia and osteospermum for April 1 or May 15. Our models project the least amount of heating is required on a per-crop basis when grown at 58 or 63°F in all seven locations tested. 
 
For example, osteospermum grown in Charlotte, N.C., at 58°F instead of 73°F would save growers 26 percent on heat if grown for a finish date of April 1. Growers would save 56 percent on heat if grown for a finish date of May 15. Similarly, a greenhouse located in Grand Rapids, Mich., would consume 14 to 28 percent less heat per square foot per crop if grown at 63°F compared with 73°F.
 
For dahlia and osteospermum, it was more energy efficient to transplant earlier in the spring and grow crops at a cool temperature than to transplant later and finish warm. Furthermore, plant quality was considerably higher when crops were grown at these lower temperatures, especially in osteospermum. For many of the other crops we have discussed in this article series, such as seed geranium (see Greenhouse Grower, September 2009), energy consumption was lowest when crops were grown more quickly by using a warmer temperature (at least 68°F). Therefore, energy-efficient production of a variety of bedding plants requires some crops to be grown cool and others to be grown in separate greenhouse sections at warmer temperatures.
 
The cost of energy for heating is just one of the many production expenses for greenhouse crops. Other factors, such as the number of crop turns and labor availability, should also be considered when choosing the most economical growing temperature for each floriculture crop producer. The impact of temperature and DLI on plant quality, and response variability among cultivars, should also be considered. 

Leave a Reply

More From Annuals...

January 16, 2018

Ball Horticultural Company, KeyGene Announce Successful Genome Sequencing of Impatiens

The companies’ breakthrough high-quality genome sequence and assembly of I. walleriana should lead to more efficient breeding and identification of disease resistance markers for important industry solutions.

Read More
Golden-State-Bulb-Begonia-Feature

January 16, 2018

PanAmerican Seed Buys Begonia Product Line From Golden State Bulb Growers

The acquisition of the popular AmeriHybrid and On Top begonia genetics expands PanAmerican Seed’s assortment in this important class.

Read More

January 16, 2018

20 Colorful Foliage and Tropical Plants for Garden Interest

Add a bit of the tropics to your product mix with new foliage and tropical plant varieties that offer bold colors and distinct patterns.

Read More
Latest Stories

January 4, 2018

Stand-Out New Varieties That Keep D.S. Cole Growers Co…

See what new varieties stood out to Doug Cole, owner of D.S. Cole Growers in Loudon, NH, this year.

Read More
Begonias-I’Conia-Series-Dümmen-Orange-Miss-Montreal

December 19, 2017

34 New Flowering Annuals to Brighten Up Your Product Mi…

Consumers will soon have the opportunity to experiment with colorful, big-impact blooms in their containers and landscapes. Here are 31 new introductions to consider that will color-up your product mix.

Read More
Eason-New-Calibrachoa-Hi-Graft

November 14, 2017

Eason Horticultural Resources Introduces New Decorative…

Created by Hishtil Nursery in Israel, the new decorative forms of calibrachoa feature an 8- to 12-inch stem and come in four colors of calibrachoa blooms on top.

Read More
Helianthus Sunfinity (Syngenta Flowers)

September 3, 2017

Growing Tips for Helianthus Sunflower ‘Sunfinity…

This annual sunflower is a profuse bloomer with strong branching that produces multiple flowers per plant from spring to fall.

Read More

August 29, 2017

27 New Impatiens for Spring Color in 2018

Gardeners love impatiens because they are one of the few plants that offer stand-out, splashy blooms for shady areas, and in some cases full sun. There's no shortage of new introductions this year to choose from for your 2018 product mix. Here are 27 new and improved varieties to consider offering to your customers.  

Read More
Candy Tops Snapdragons Series (Sakata Ornamentals)

August 3, 2017

Five Characteristics Breeders Want in Top-Performing Sp…

New spring annuals have to provide something for everyone — longevity, durability, performance, and more — if they want to meet breeders’ high standards for market-worthy plants.

Read More
Petunia 'Headliner Pink Sky" (Selecta)

August 3, 2017

Why Eccentricity is the New Black in Spring Annuals

Consumers judge plants by appearance, color impact, and ease of maintenance, which is why retailers want new spring annuals that are novel standouts.    

Read More
Petunia 'Amore Mio' (Danziger)

June 8, 2017

AmericanHort Update on Genetically Engineered Petunias

AmericanHort is actively assisting affected plant breeders, distributors, growers, and retailers as the genetically modified petunia regulatory response continues. Since the last update, there have been several changes to the list of petunias confirmed or suspected of being genetically engineered and therefore unauthorized to be imported or sold. Also, the list of recognized laboratories for petunia variety confirmation testing has expanded. Most importantly, petunia varieties on the USDA-APHIS Biotechnology Regulatory Services (BRS) list require an APHIS Form 2000 for importation. APHIS also began requiring that any Petunia spp. Shipments, not including regulated GE varieties, must be accompanied by a list of variety names. This resulted in some inspection delays at the USDA-APHIS plant inspection station in Atlanta over the past two weeks. In response, AmericanHort has negotiated a more flexible approach with APHIS, and new guidance has just been posted for importing Petunia plants, cuttings, or seed. The new guidance allows […]

Read More

May 25, 2017

Genetically Modified Petunia Update: Breeders Take Swif…

Now that the initial shock of genetically engineered petunias is wearing off, breeders continue testing for tainted stock and look toward the future. On the consumer side, uncertainties remain.  

Read More

May 23, 2017

USDA-APHIS Bulletin on Unauthorized Distribution of Gen…

On May 2, 2017, USDA-APHIS was informed that an orange petunia variety was potentially genetically engineered and had been imported and moved interstate without required authorization by APHIS. This led to testing of numerous petunia varieties, which confirmed this particular variety and several others are genetically engineered, and meet the regulatory definition of a regulated article under APHIS regulations. APHIS continues to work with the industry to ensure unauthorized GE petunias are not distributed in the United States.

Read More
Petunia F1 African Sunset from American Takii

May 22, 2017

Genetically Modified Petunia Update: Question and Answe…

AmericanHort’s key role interfacing with the USDA on the recall of genetically modified petunias has helped the horticulture industry rapidly address the problem. Senior Vice President Craig Regelbrugge talks about recent updates, the impact on the industry, and where it goes from here.

Read More

April 25, 2017

41 New Vegetative Petunias From California Spring Trial…

With the abundance of new introductions for the 2018 retail season, we’ve made it easier for you to sift through them by separating out the vegetative petunias from the Northern sites, which includes selections from Westhoff Flowers, Sakata Ornamentals, Danziger, Proven Winners, and Syngenta flowers.

Read More
Zinnia Solmar Series (Floranova)

March 17, 2017

Phlox, Zinnias, and More for 2018 From California Sprin…

We asked breeders to share with us pictures and information on some of the great new annuals that you'll see at California Spring Trials 2017. They didn't let you down.

Read More
Cosmos ‘Apollo’ (Floranova)

March 14, 2017

Begonias, Dahlias, and More for 2018 from California Sp…

We asked breeders to share with us pictures and information on some of the great new annuals that you'll see at California Spring Trials 2017. They didn't let you down.

Read More
Limbo GP burgundy picotee

March 7, 2017

New Petunias and Calibrachoas for 2018 from California …

We asked breeders to share with us pictures and information on some of the great new petunias and calibrachoas that you'll see at California Spring Trials 2017. They didn't let you down.

Read More
Sea Breeze Catharanthus combo

December 2, 2016

Four Mixed Container Trends To Watch

Mixed containers are still one of the best-selling SKUs at retail. Pay attention to these four trends that are making their mark on multi-liner mixes and combination containers.

Read More

September 7, 2016

Check Out The Best Annuals For Attracting Bees And Butt…

Public interest in protecting bees and other pollinators has initiated a new market for flowers that are good food plants for pollinators. Here's a list of annuals Michigan State University Extension recommends that are attractive to bees and other pollinators.

Read More

September 6, 2016

10 Colorful Spring Plants For Sales In 2017

Trends with plants come and go, but color always sells. These spring crops for 2017 offer color choices ranging from bold and vibrant hues to understated, softer tones, and they’re versatile enough to be used in baskets, containers, beds, and borders.

Read More