Energy-Efficient Annuals: Petunias

Energy-Efficient Annuals: Petunias Images

Escalating fuel costs have made it important for greenhouse growers to improve production efficiency and schedule crops more efficiently. At Michigan State University (MSU), we have performed experiments with many seed-propagated annuals to quantify how temperature and daily light integral (DLI) influence flowering time and plant quality. In the sixth article of this series, we present crop timing data on petunias and then use this information to estimate greenhouse heating costs at different locations, growing temperatures and finish dates.

Petunias are among the top 10 bedding plants produced in the United States. In 2008, the 15 largest floriculture-producing states collectively sold 34.5 million flats, pots and hanging baskets at a total wholesale value of $120 million. Among the different species and hybrids of petunias available, our studies have included grandiflora petunia ‘Dreams Neon Rose,’ milliflora petunia ‘Fantasy Blue,’ and spreading petunias ‘Easy Wave Coral Reef’ and ‘Wave Purple.’

Materials and Methods

Seeds of each petunia variety were sown in 288-cell plug trays by C. Raker & Sons, then grown in controlled environmental growth chambers at MSU at 68°F (20°C). Inside the chambers, the photoperiod was 16 hours (an inductive long day) and the DLI was 9 to 11 mol∙m¯²âˆ™d¯¹.

When plugs were ready for transplant (27 to 35 days after seed sow), they were thinned to one seedling per plug and transplanted into 4-inch pots and grown in greenhouses with constant temperature set points of 57, 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 a combination of shade curtains and different supplemental lighting intensities from high-pressure sodium lamps.

Some petunia varieties such as ‘Dreams Neon Rose’ do not require long days for flowering, but flower faster if grown under long days. Other petunia varieties such as ‘Wave Purple’ are obligate long-day plants and must be grown under long days for flowering. Therefore, when producing petunias under naturally short day lengths (less than 13 to 14 hours), photoperiodic lighting will accelerate flowering and shorten cropping time.

Our experiments were performed twice to obtain average DLIs that ranged from 4 to 20 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 20 mol∙m¯²âˆ™d¯¹ is typical for a mid- to late spring day. The flowering date was recorded for each plant when the first flower opened, and at that time, plant height, number of leaves and number of flowers and flower buds 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 scheduling models were validated by growing petunias at three different constant temperatures to compare predicted flowering times with actual times. The Virtual Grower 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 United States.

Results

In all petunia varieties, time to flower decreased as average daily temperature increased. For example, in ‘Dreams Neon Rose’ grown under a DLI of 10 mol∙m¯²âˆ™d¯¹, time to flower from a 288-cell plug decreased from 40 days at 58°F to 20 days at 73°F (Figure 1). At the same DLI, ‘Wave Purple’ flowered almost five weeks later at 58°F versus 73°F (Figure 2). Petunia ‘Fantasy Blue’ grown under 10 mol∙m¯²âˆ™d¯¹ and at 58, 63, 68, 73 or 79°F flowered in 27, 22, 19, 17 and 15 days, respectively. Petunia ‘Easy Wave Coral Reef’ grown under 10 mol∙m¯²âˆ™d¯¹ and at 58, 63, 68 or 73°F flowered in 46, 35, 28, 23 and 19 days, respectively.

An increase in DLI also accelerated flowering of petunia. For example, for plants grown at 63°F, time to flower decreased by four days in ‘Dreams Neon Rose,’ 13 days in ‘Fantasy Blue,’ and 11 days in ‘Easy Wave Coral Reef’ and ‘Wave Purple’ when DLI increased from 4 to 10 mol∙m¯²âˆ™d¯¹. The estimated saturation DLI for the shortest time to flower was 10.5 mol∙m¯²âˆ™d¯¹ for ‘Dreams Neon Rose,’ 16 mol∙m¯²âˆ™d¯¹ for ‘Easy Wave Coral Reef,’ and 14 mol∙m¯²âˆ™d¯¹ for ‘Wave Purple.’ In other words, increasing the DLI above these values did not shorten crop time. Flowering time continued to decrease as DLI increased for ‘Fantasy Blue’ and thus, the saturation DLI is greater than 20 mol∙m¯²âˆ™d¯¹. Using this research data, we identified dates that 288-cell plugs grown under long days need to be transplanted for two market dates when grown at different temperatures under long days (Table 1).

The number of flower buds at first flowering increased as average daily temperature decreased and as DLI increased. For example, in petunia ‘Wave Purple’, the number of flower buds increased by 75 percent as DLI increased from 5 to 15 mol∙m¯²âˆ™d¯¹. In all petunias, plants had the fewest flowers when grown at the warmest temperature (79°F) and under the lowest DLI (4 mol∙m¯²âˆ™d¯¹). Plant height at flower increased as DLI decreased.

As most growers already know, crop timing varies significantly among petunia varieties. In the four petunias we studied, crop timing at 68°F varied from 19 to 37 days even when light conditions were nearly identical during the plug and finish stages. Similarly, increasing the DLI had different promotive effects on the varieties studied. However, all crops flowered faster, and plants were of higher quality, when the DLI was increased to at least 10 mol∙m¯²âˆ™d¯¹.

Heating Costs

This crop timing information can be used with Virtual Grower to identify the most energy-efficient production temperature for different dates and locations. According to our predictions, heating costs for a crop of petunia ‘Dreams Neon Rose’ grown for April 1 in San Francisco, Calif., Tallahasee, Fla., Charlotte, N.C., or Fort Worth, Texas, would be 13 to 38 percent lower at a constant 58°F versus 73°F (Table 2). To produce the same crop in northern locations such as Grand Rapids, Mich., New York, N.Y., or Cleveland, Ohio, heating costs per square foot would be 22 to 29 percent higher at 58°F versus 73°F. In other words, it is more energy-efficient for growers in the north to start spring production later and grow at a warmer temperature.

Petunia ‘Wave Purple’ grown under 10 mol∙m¯²âˆ™d¯¹ for April 1 in Grand Rapids, Mich., New York, N.Y., or Cleveland, Ohio would cost 9 to 21 cents less per square foot if grown at 68 or 73°F versus 58°F. Therefore, a grower with a half-acre greenhouse would save $1,960 to $4,574 on heating costs per crop by transplanting later and growing warm. In addition, ‘Wave Purple’ grown at 68 or 73°F would flower four to five weeks earlier than at 58°F, which would make production space available for additional crops.

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 overhead costs, should also be considered when choosing the most economical growing temperature for each floriculture crop producer.

Leave a Reply

More From Annuals...
Gaillardia x grandiflora 'Arizona Apricot'

February 25, 2015

National Garden Bureau Designates 2015 As Year Of The Gaillardia

Gaillardia, also known as the blanket flower, is a member of the sunflower family (Asteraceae) and a long-blooming pollinator plant. It is fitting that the National Garden Bureau has specified 2015 as The Year of the Gaillardia.

Read More
IPPS Sharing Plant Production Knowledge Globally Logo

February 25, 2015

International Plant Propagators Western Region Sets Annual Meeting Date

The annual meet for the International Plant Propagators' Society (IPPS) Western Region has been set for this September. It will take place September 23 to 26 in Modesto, Calif., and will include learning sessions, tours to local nurseries, a research poster display and poster presentations, various networking opportunities and an awards banquet to close the event.

Read More
Evolvulus Blue My Mind

February 24, 2015

Blue Ribbon Bloomers For Greenhouse Production

Grow what consumers want! Surveys show that blue is one of the top preferred colors of today’s consumers. Here are twelve top recommended blue-flowering Proven Winners annuals and perennials to suit your spring production cycle.

Read More
Latest Stories

February 18, 2015

California Spring Trials Sneak Peek: New Annuals For 20…

If you're like us and you can't wait until the 2015 California Spring Trials to see some of the new genetics that will be hitting the market in 2016, never fear. We contacted the breeders who will be displaying their new varieties in California in April, and they gave us a sneak peek. Check out our slideshow to see some of the new annuals making their debut to the trade this spring.

Read More

November 14, 2014

First Vegetatively Propagated All-America Selections (A…

All-America Selections (AAS) honors two vegetatively propagated impatiens with AAS winner status.

Read More

October 13, 2014

Growing Tips For Verbena

Rich Schoellhorn, product manager at Proven Winners, shares some tips for growing verbenas successfully.

Read More

October 13, 2014

Greenhouse Grower 2014 New Varieties Guide: Petunias [S…

Greenhouse Grower asked more than 40 breeders to send photos of new introductions they think are worth your attention. The result is the 2014 New Varieties Guide. See what petunias made the cut.

Read More

June 12, 2014

New Begonia Variety And Coleus Series, Plus Two Lobelia…

Terra Nova Nurseries introduces seven new varieties and one new series.

Read More

May 27, 2014

Two New Salvias Added To Southern Living Plant Collecti…

Two new salvia varieties are now available exclusively to growers from the Southern Living Plant Collection and Sunset Western Garden Collection.

Read More

May 9, 2014

New Petunias Making Their Debut In 2015

Take a look at the new petunia varieties that will be making their appearance in 2015.

Read More

April 23, 2014

Foliage Begonias May Be A Big 2015 Trend [Spring Trials…

A number of breeders debuted their rex begonia and begonia hybrid lines at 2014 Spring Trials.

Read More
Petunia 'Success Violet' from Benary

April 11, 2014

What’s New With Petunias For 2014? [Slideshow]

Breeders are rolling out great new petunia introductions for 2014. Take a look at the variety of petunias they have to offer.

Read More
Verbena 'Superbena Royale Whitecap' from Proven Winners

November 11, 2013

Three New Verbena Superbena Introductions From Proven W…

Three new varieties have joined the verbena Superbena line-up this year: 'Superbena Royale Plum Wine,' 'Superbena Royale Whitecap' and 'Superbena Violet Ice.'

Read More
Calibrachoa 'Mini Famous Double Blue' from Selecta

October 17, 2013

6 New Calibrachoa For 2013

Check out these lovely new introductions in calibrachoa.

Read More

October 10, 2013

Begonia ‘Silhouette Lemon Rose’ Doubles The Bloo…

Begonia ‘Silhouette Lemon Rose’ is a striking begonia hybrid with phenomenal basal and lateral branching. Plant sterility gives maximum continual flowering throughout the season with double the bloom number of a traditional non-stop begonia. Dark mahogany foliage with contrasting emerald green veining provides a dramatic contrast to the soft lemon yellow 1.5- to 2-inch diameter blooms that blush apple blossom pink in high light. This easy-care beauty is ideal for mixed pots and containers, hanging baskets or the summer border. For more information, visit PlantHaven.com

Read More
Petunia 'Flash Mob Bluerific' Burpee Home Gardens

October 7, 2013

18 New Petunias To Add For 2014

Tried and true, petunias are a garden staple. Here are some new introductions breeders are rolling out for your consideration in 2014.  

Read More
Verbena 'Hurricane Hot Pink' from Westflowers

October 7, 2013

New Verbena For 2014

Check out these eight new verbena varieties and consider them for your 2014 greenhouse production.  

Read More
Dahlia Dalaya Shari from Selecta

September 25, 2013

4 New Dahlias For Your 2014 Season

Looking for new dahlia varieties to incorporate in your crop mix? Here are 4 beauties your customers will love.  

Read More
'Wall Street' Coleus from Dummen/Red Fox

September 25, 2013

4 Colorful New Coleus For 2014

Gorgeous foliage makes these new introductions must-haves for next year.  

Read More

September 16, 2013

9 Geraniums For Your 2014 Spring Season

Check out these 9 new introductions featured in Greenhouse Grower's 2013 New Varieties Guide to consider for your spring production.

Read More
Begonia 'Breezy Pink'

September 16, 2013

13 New Begonias For 2013

Looking for something new in begonias? Check out these 13 new variety introductions for this popular genus.

Read More