When To Light and When To Shade: Ready Research Results

When To Light and When To Shade: Ready Research Results

Plants increase in mass, or dry weight, through photosynthesis. Photosynthesis is the process that harvests light energy to drive critical processes resulting in plant growth. Why is increasing photosynthesis important? Increased photosynthesis is associated with increased flowering, increased plant quality and increased post-harvest life. How much, or how fast, a plant can photosynthesize depends on light intensity, carbon dioxide and temperature.

Although much work was done during the 1960s and ’70s, there is little recent research on how changing light intensity, carbon dioxide and/or temperature affect photosynthesis of commonly grown greenhouse crops today. For this reason, we started a research project at the University of Minnesota with support from the Floriculture and Nursery Research Initiative and the American Floral Endowment to provide growers with answers to questions such as: How much supplemental light should I add to maximize photosynthesis? What is the impact on photosynthesis of adding supplemental carbon dioxide? When light levels decrease, should I reduce temperature? When should I close a light reduction curtain so it does not reduce photosynthesis and plant quality?

In this article, we will briefly go over preliminary results that answer these questions: How does increasing light intensity affect photosynthesis of some common greenhouse crops, and do optimal light intensities change in a plant canopy? We will also translate that data into recommendations on how you can use this new information in your facility. We believe growers can use this new information to help 1) increase crop quality, 2) decrease energy input costs and 3) minimize unnecessary plant stress that could decrease flowering.

What We Learned

In all cases, photosynthesis increased as light intensity increased up to some maximum light level. As light intensity increased further, photosynthesis did not increase further (i.e. it is light-saturated).

What differs between species is the light intensity at which photosynthesis saturates. There are plants in which photosynthesis saturates at low light intensities, such as 200 umol m¯² s¯¹ (approximately 1,000 footcandles). In other plants, photosynthesis saturates at intermediate light levels, such as 400 umol m¯² s¯¹ (2,000 footcandles). Lastly, there are plants in which photosynthesis saturates at high light levels (600 um¯² s¯¹, 3,000 footcandles). Examples of approximate light levels when photosynthesis saturates are shown in Table 1.

Light Intensities In Canopies

The maximum light intensities for photosynthesis in Table 1 are for an unshaded, completely exposed leaf. As our crops grow, the canopy closes if plants are not regularly spaced. This means you will have to provide higher light levels at the top of the canopy in order to achieve optimal light levels and maximum photosynthesis in the middle of the crop canopy. How much a canopy reduces light transmission through shading depends on many things, including species, spacing and leaf number.

For instance, we looked at how leaves of different species reduce light to lower leaves. Table 2, online at GreenhouseGrower.com, shows how much photosynthetically active radiation (PAR) different greenhouse crops transmit–half an inch to 1 inch below a fully expanded leaf on a clear day at noon outdoors. Note that light transmission varies from 5 to 12 percent (i.e. some species filter twice as much light as others). Those species that filter more light will require increased light intensity as a canopy closes compared to those that transmit more PAR.

We also measured how light intensity is reduced as you move down through a canopy of two species: coleus and Panicum virgatum (switchgrass). You can see that coleus filters light more than the grass as you move down through the canopy. This means you will need more light at the top of a coleus canopy than at the top of a panicum canopy to achieve 2,000 footcandles at mid- or lower leaves in a canopy.

Do Your Own Tests

Interested in doing similar tests at your operation? Let’s get you started:

1) Buy a light meter that can measure light in micromoles (umol m¯² s¯¹). Micromoles are the units that are associated with photosynthesis. Units commonly used in greenhouse control systems that measure light in joules, watts or footcandles do not accurately measure only light that plants use for photosynthesis. Photosynthetic light is the only light that we should be concerned with for supplemental lighting for photosynthesis in greenhouse crops!

2) Install light meters/sensors that control supplemental lighting and/or automated light reduction curtains at plant level inside the greenhouse. The standard procedure of mounting light meters outdoors above a greenhouse is effectively useless for growing crops indoors.

3) Group crops by how much light they can use (low, medium, high light-saturating crops, see Table 1) and provide supplemental lighting based on this.

4) See how much your light intensity decreases as you go down through your crop canopy. Increase light intensity at the top of the plant as a canopy closes to achieve maximum photosynthesis levels in the middle of the canopy. Again, this can be done automatically if light meters are placed in a canopy indoors in the middle of a canopy!

5) Use of greenhouse coverings (removal, shading, etc.) should be based on light effects on crop photosynthesis (i.e. high light requiring crops may need to be in greenhouses with high light transmission, have coverings replaced more often or shading sprayed on greenhouses later than low light requiring crops). In contrast, low light requiring crops could stay in darker, older greenhouses.

Leave a Reply

More From Disease Control...
Coleus 'Colorblaze Velveteen' (2015 University of Tennessee Field Trials)

November 28, 2015

2015 University of Tennessee Gardens (Knoxville and Jackson, Tenn.) Field Trials Results

See the 2015 field trials results (includes photo gallery) for University of Tennessee Gardens in Knoxville and Jackson, Tenn.

Read More
Feature Image Cob 700 (NewLux)

November 28, 2015

16 LED Lighting Solutions For Your Greenhouse

Narrowing in on the right LED lighting product often comes down to considering your specific crop needs and growing requirements to see what works best for your application. Here are 15 LED products to take into account when choosing the right fit for your greenhouse.

Read More
Begonia 'BabyWing Red' (2015 Louisiana State University Field Trials)

November 27, 2015

2015 Louisiana State University (Hammond, La.) Field Trials Results

See the 2015 field trials results (includes photo gallery) for Louisiana State University in Hammond, La.

Read More
Latest Stories
Phytophthora On Poinsettia

November 19, 2015

Florida Researchers Help Ornamental Growers Reduce Fung…

A team of scientists at the University of Florida have found a way to help growers reduce pesticide use and potentially save millions for the ornamental industry.

Read More
Nemasys And Millenium Beneficial Nematodes from BASFm_Nematodes

October 7, 2015

How BASF’s UK Biological Production Facility Expa…

BASF has expanded its biologicals production facility in Littlehampton, UK. The new capacity increases the company’s ability to double the production of beneficial nematodes and inoculants.

Read More

September 23, 2015

New Crop Protection Products And Label Updates

Here are some of the most recent products released and label updates for crop protection agents in the greenhouse and nursery market. Fame Fungicides (FMC Corp.) FMC Corp. has introduce Fame fungicides, a family of FRAC 11 group (Strobilurin) products that delivers fast-acting, patented fluoxastrobin protection against major soil and foliar diseases. Rainfast in 15 minutes, Fame fungicides can be used on most greenhouse and nursery plants and provide fast foliar and root uptake. “Proven by university research, Fame fungicides offer fluoxastrobin action, which ensures a high degree of systemic activity to provide very rapid disease protection and stop further growth of established disease,” says Naimur Rahman, strategy and fungicide marketing product manager for FMC. The Fame fungicide family includes: • Fame SC: a suspension concentrate fungicide containing fluoxastrobin that controls major diseases, including anthracnose, downy mildew, powdery mildew, scab and leaf spot. It provides rapid foliar and root uptake […]

Read More
Offshore farm profiles Dummen Orange Las Mercedes Solanaceas GH

September 8, 2015

Dümmen Orange Implementing Consistent Standards On All …

Owning and operating several locations can be a challenge in maintaining consistent quality and cleanliness across the board. This is true of both breeders and growers. But those who do it right have invested in technology and practices that ensure that plant quality matches, no matter where their plants are shipped from. That’s the goal for Dümmen Orange. Now the world’s largest producer of unrooted cuttings, the company has a combined 150 hectares or 370 acres of production space worldwide, dedicated to cuttings production. Recent acquisitions of product portfolios, both this year and in the past few, has raised the company’s cuttings production expectation to more than 1.4 billion, including 350 million in North America. It has farms all over the world (see the 2015 Top Cuttings Producers ranking to see where), and produces cuttings for its own genetics, as well as collaborating with more than 30 third-party breeders across all […]

Read More
r3bv2 disease

May 20, 2015

SAF And AmericanHort Ask Government To Take Ralstonia O…

The Society of American Florists (SAF) and AmericanHort want Ralstonia solanacearum, Race 3, Biovar 2 (R3Bv2) taken off a list of animal and plant diseases that the federal government has determined could be misused as terrorist weapons. SAF and AmericanHort submitted formal comments together on the horticulture industry’s science-backed position on the matter. According to Lin Schmale, SAF’s senior director of government relations, extensive research has proven R3Bv2 does not belong on the government’s list of animal and plant diseases that can be misused as terrorist weapons. Every two years, USDA’s Animal and Plant Health Inspection Service (APHIS) requests a public review of the Select Agent list, asking for comments on whether plant or animal diseases should be taken off the current list or added to it. In the floral industry, R3Bv2 can have a devastating impact on geranium (pelargonium) crops, Schmale says, and both the potato and tomato industries also could be adversely affected by introduction […]

Read More

May 13, 2015

BASF’s Empress Intrinsic Fungicide Is Approved Fo…

BASF’s Empress Intrinsic brand fungicide received supplemental labeling, providing California growers with an effective drench fungicide for disease control and plant health. The supplemental labeling is for use on herbaceous and woody plants in greenhouse, nursery container and field production in California. Empress Intrinsic fungicide provides protection against the four major root and crown disease pathogens: fusarium, phytophthora, pythium and rhizoctonia. Research shows Intrinsic fungicides control the broadest range of ornamental diseases while improving plant resilience to quality and reducing stresses that commonly occur during commercial production, handling and transportation. “More and more growers across the country are discovering the benefits of Empress Intrinisic brand fungicide treatments at propagation for rooted plugs, cuttings and seedlings, and in drench applications on transplants during the production cycle to protect against the major root diseases,“ says Joe Lara, senior product manager for BASF ornamentals. “A BASF fungicide program utilizing Pageant Intrinsic and Empress Intrinsic […]

Read More

April 20, 2015

Three Michigan State University On-Demand Webinars Offe…

The first rule of effective insect and disease control for vegetables is to take action to prevent problems before they occur. But in order to do that, you need to have an effective pest and disease management strategy in place that incorporates best practices to ensure a successful outcome. Michigan State University offers three pest and disease management on-demand webinars that will get you started and keep you on the right track.

Read More

April 15, 2015

BASF’s Pageant Intrinsic Fungicide Registration A…

The state of California has approved the supplemental label registration of Pageant Intrinsic brand fungicide for disease control in the commercial production of greenhouse-grown tomatoes and tomato transplants for the home consumer market.

Read More

March 23, 2015

BioSafe Makes Label Changes To OxiPhos And ZeroTol 2.0

There have been some recent label changes made to the BioSafe Systems product OxiPhos, a systemic bactericide/fungicide that reduces downy mildew spores when tank mixed with ZeroTol 2.0.

Read More

March 23, 2015

Nufarm Fungicides Now Registered For Use On Edible Crop…

Nufarm Americas announced label expansions for two of its fungicides that will provide more pest management options for the ornamental industry. The Cleary 3336 F and EG fungicides are now registered for use across a wider range of edible crops, including select greenhouse vegetables and transplants, herbs and backyard fruit.

Read More

March 11, 2015

Research Gives Clues For Preventing Coleus Downy Mildew

Maintaining awareness of coleus downy mildew is more important than ever to safeguard these attractive plants for reliable garden performance.

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…

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

October 6, 2014

EPA Registration Granted To Stockton’s Timorex Go…

Timorex Gold, a broad spectrum fungicide, has received EPA registration in the U.S. for disease control on organic and conventional crops.

Read More

August 5, 2014

Prevention Measures For Impatiens Downy Mildew Start At…

Impatiens downy mildew is a fast-moving disease that can quickly go from bad to worse if conditions are right. In case you missed it, here are some of the highlights from Ann Chase's (Agricultural Consulting) downy mildew update at Cultivate'14.

Read More

July 22, 2014

Spray Coverage Key To Uniform Pest And Disease Control …

Greenhouse growers need to understand proper spray application coverage when applying pesticides and growth regulators to ensure successful treatment results.

Read More
Jeff Rich

July 18, 2014

Removing The Mask Of Phytophthora

Phytophthora is the number one disease of floriculture and nursery crops nationwide. Here are some effective measures growers can take to reduce the occurance of this pathogen, known as "the plant destroyer."

Read More

June 27, 2014

Biocontrols Can Be Highly Effective With Serious Commit…

Biocontrols can be very effective when the greenhouse operator makes a serious commitment to using them for integrated pest control. See how Parkway Gardens has successfully used biocontrols for the last nine years.

Read More
[gravityform id="35" title="false" description="false"]