Energy-Efficient Annuals: Perfecting Temps & Light

Energy-Efficient Annuals: Perfecting Temps & Light

Bedding and garden plants are the largest category of floriculture crops in the United States with a wholesale value of $1.76 billion in 2007. Scheduling these crops in flower for specific market dates, at different times of the year, can be a challenge. In addition, most bedding plants are produced when energy for heating a greenhouse is a large production cost, particularly in northern climates. To optimize the greenhouse environment and produce crops as energy efficiently as possible, more information is needed on how bedding plants respond to temperature and light.

 
Figure 1. The effects of average daily temperature on time to flower and
number of flower buds in petunia. Plants were grown under a 16-hour
photoperiod and an average daily light integral of 20 mol∙m−2∙d−1. The
photograph was taken four weeks after transplant from a 288-cell plug tray.

During the past several years, we have performed greenhouse experiments at Michigan State University to study the effects of temperature and light on crop timing and plant quality of many popular seed-propagated annuals. In this 12-part series, we will present research-based information so that these crops can be scheduled in a more energy-efficient, predictive manner. We will also use computer software (Virtual Grower) to predict how different scheduling options influence greenhouse energy consumption. This first article reviews how temperature and light influence crop timing and plant quality

Average Daily Temperature

The rate of plant development (time to flower) is controlled by the 24-hour average daily temperature (ADT). Many greenhouse crops develop a certain number of leaves before flowering. Therefore, how fast or slow a crop develops can be controlled by raising or lowering the ADT. For example, petunia ‘Dreams Red’ grown at 79°F (26°C) flowered 19 days earlier than plants grown at 59°F (15°C) (Figure 1). Some growers have lowered the night temperature in an attempt to lower energy costs for greenhouse heating. However, this practice delays development and increases production time unless the day temperature is increased so that the ADT is the same. The net result can be that plants grown at cool temperatures can use the same or more heating fuel (spread out over more time) and fewer crop turns are possible.

Figure 2. Conceptual diagram of the rate of plant development (such as
leaf unfolding) in relation to the average daily temperature. The
shape of the curve varies from crop to crop.

The rate of plant development stops when the ADT is near the base temperature and increases linearly as temperature increases until some optimum temperature is reached (Figure 2). With further increases in temperature, the rate of plant development begins to decrease and thus delay flowering. The base and optimum temperature vary among species, and until now, little information on bedding plants has been available. In our greenhouse experiments, plants were grown at four or five different ADTs between 57 and 79°F (14 and 26°C) and flowering time was recorded.

Plants grown at cooler temperatures often have more flowers at first flowering than plants grown at warmer temperatures. For example, petunia ‘Dreams Red’ grown at 59 or 64°F had 15 more flower buds at flower than plants grown at 79°F (Figure 1). This is especially a concern under light-limiting conditions. Higher plant quality at a cooler temperature can occur because plants are in the greenhouse longer and have more time to harvest light for photosynthesis. Therefore, there can be a trade-off between producing a high-quality crop and short crop timing. We will present our research information on how individual crops respond to temperature and light, and the impacts on energy consumption, in future articles of this series.

Figure 3. Effects of average daily temperature and daily light integral (DLI)
on time to flower in marigold ‘Moonstruck Orange.’ Plants were grown under a
16-hour photoperiod. Photograph was taken eight weeks after transplant
from a 288-cell plug tray.

Daily Light Integral

Flowering time and plant quality can also be influenced by the total amount of photosynthetic light (daily light integral, or DLI) that a plant receives. DLI is the cumulative amount of light received during a 24-hour period and is expressed as moles per square meter per day (mol∙m¯²âˆ™d¯¹). In the north (above 35°N latitude) and during the winter, the DLI inside a greenhouse without supplemental lighting can be less than 5 mol∙m¯²âˆ™d¯¹. In late spring, the greenhouse DLI can reach 25 to 30 mol∙m¯²âˆ™d¯¹ before shading is used to prevent unwanted high temperatures.

Many crops grown under a high DLI flower faster than those grown under a low DLI. For example, marigold ‘Moonstruck Orange’ grown at 63°F and under 12 mol∙m¯²âˆ™d¯¹ flowered 8 days earlier than plants grown at the same temperature, but under 5 mol∙m¯²âˆ™d¯¹ (Figure 3). The acceleration of flowering under a high DLI can be related to various factors, including: 1) greater photosynthesis; 2) formation of fewer leaves before flower initiation; and 3) warmer plant temperature. Species that produce fewer leaves before flowering when grown under a high DLI are described as having a facultative irradiance response. As with temperature, there is a saturation value at which any further increase in DLI has little or no effect on flowering time.

A higher DLI can also improve crop quality. Plants grown under a high DLI typically have smaller and thicker leaves, thicker stems, shorter internodes, increased rooting and more lateral branches and flowers. This is why plants finished in late spring are generally of higher quality than those produced earlier. Plants in our experiments were grown under DLIs ranging from 4 to 20 mol∙m¯²âˆ™d¯¹ to determine the influence of DLI on flowering. DLI responses for different annual crops will be discussed in future articles.

Photoperiod (day length) can also influence crop timing because many plants flower in response to short days (for example, poinsettia) or long days (for example, petunia). Other plants are day neutral (not affected by photoperiod). For energy-efficient greenhouse production, photoperiod-sensitive plants should be grown under a photoperiod that promotes flowering. In our greenhouse experiments, most of the annuals studied were all long-day crops, so plants were grown under a 16-hour photoperiod.

Leave a Reply

More From Plant Culture...

March 2, 2015

Student Flash Mob At TPIE Has Roots In Floriculture

The local FFA students who entertained TPIE attendees in 2014 and 2015 received industry donations of plants and a greenhouse structure to help expand their horticultural program.

Read More
Rose Rosette on Knockout rose, May 2013. Photo credit: Alan Windham, University of Tennessee

March 2, 2015

Rose Rosette Disease Fight Gets A Boost From Government-Backed Funding

In 2014, $4.6 million was awarded through the Farm Bill to tackle rose rosette disease, a devastating pathogen that affects one of the industry’s most important crops.

Read More
Fig 1 Leafy Gall On Leucanthemum Becky

March 2, 2015

How To Prevent Leafy Gall Before You Lose Plants

Leafy gall is a nasty disease that can go undetected until plant damage is done. Take these steps to protect your crops from infection.

Read More
Latest Stories

February 11, 2015

Infusion Technology Boosts Seed Performance, Study Sugg…

Seven-year-old wheat seed germination can increase by as much as 83 percent, according to a Vital Force Technology Study that looks at the effects of energy infusion technology on plant vitality.

Read More

February 3, 2015

American Floral Endowment Accepting Research Pre-Propos…

If you are pursuing a floriculture research project, now is the time to apply for funding through the American Floral Endowment. Research pre-proposal applications for 2015-2016 funding are due to AFE by June 1, 2015.

Read More

January 27, 2015

Marijuana’s Trajectory And Ascent To Horticultural Cr…

Marijuana growing is poised for change as growers and researchers focus on improving production practices.

Read More

December 9, 2014

Greenhouse Production: Two Years Of Basics & Beyond…

Greenhouse Grower's Basics & Beyond articles cover some of the latest news and research going on in greenhouse production. Here are article links for the last two years.

Read More
GrowIt! App Wins Gold At Design100 2014 US Mobile & App Design Awards

November 24, 2014

GrowIt! App Wins Gold At Design100 2014 US Mobile &…

The social garden app GrowIt! takes the Gold Winner award at the design100 2014 Mobile & App Design Awards.

Read More

November 10, 2014

The Perennial Farm Joins HGTV HOME Plant Collection

The Perennial Farm joins the HGTV HOME Plant Collection growers' network for 2015.

Read More
AmericanHort

November 4, 2014

AmericanHort Publishes Revised American Standard For Nu…

AmericanHort announces the revised American Standard for Nursery Stock (ANSI Z60.1) is now available for industry use. The Standard reflects the consensus of the industry regarding how nursery stock — living plants other than annuals — should be specified and sold within the trade.

Read More

September 26, 2014

Master The Art Of Watering

Watering is elemental to healthy plants, but one of the hardest concepts for new employees to master in the greenhouse. Recommend these tips to start them off right.

Read More

September 16, 2014

Ball FloraPlant’s Las Limas Facility Provides Gro…

Ball FloraPlant’s Las Limas farm in Esteli, Nicaragua, is one year away from full production, but sales and quality from the two-year-old facility are right on track.

Read More
Erysimum 'Cheers' from Darwin Perennials

September 15, 2014

Darwin Perennials Takes Production Offshore In Bogota, …

With its recent purchase of a farm in Colombia, Darwin Perennials is ready to amp up supply of its perennial genetics, to provide growers with tried-and-true varieties and comprehensive production specifications.

Read More

July 23, 2014

Plan Now To Prevent Bract Edge Burn On Poinsettias

Reduce fertilizer and water, and allow your poinsettias to develop slowly during the final four weeks of production to avoid bract edge burn.

Read More

July 11, 2014

Growing Your Crops Above Their Base Temperature

Lowering temperature set points in the greenhouse may help you combat rising heating costs.

Read More

May 1, 2014

Growers Report Nutritional Problems On Geraniums

In recent weeks, several growers have contacted Michigan State University Specialists about leaf discoloration on geraniums, especially the purpling of lower leaves.

Read More

April 22, 2014

How Two Postharvest Care Products Worked On Potted Plan…

What your potted plants look like at retail translates to sales or fails. North Carolina State University researchers report on how two postharvest care products performed.

Read More
Dianthus 'Passion' from Emerald Coast Growers

March 27, 2014

Growing Dianthus Successfully

Here's some advice on transplanting and producing this classic perennial favorite.

Read More
Aquilegia canadensis

March 10, 2014

Tips For Producing Aquilegia

Advice on planting, temperature, vernalization, lighting and more on columbine from Emerald Coast Growers' head grower Josiah Raymer.

Read More
Perennials in hoop house

February 21, 2014

Overwintering Perennials: Plan Ahead To Fungicide Drenc…

Demand for perennials has increased as consumers educate themselves and seek out new and improved varieties. Overwintering perennials can become an important profit center. Here's some advice on how to overwinter successfully.

Read More
Cold damage to ipomoea

February 11, 2014

Chilling Injury On Cuttings: What To Look For

During this young plant production season when many growers receive unrooted cuttings, liners and plugs for spring production. Cuttings shippers are delaying deliveries because the tender cuttings cannot withstand the frigid temperatures.

Read More