Image courtesy of PL Light Systems

Greenhouse growers, especially those in northern latitudes, often use supplemental (also known as photosynthetic or assimilation) lighting to produce uniform, consistent and high-quality crops year-round.

Light-emitting diode (LED) fixtures are now about 40% more energy-efficient than the double-ended high-pressure sodium (HPS) fixtures [bulb (or lamp), reflector (or luminaire), and ballast], but per photosynthetic photon, the initial cost of LED fixtures, is approximately 3 to 10 times more than HPS fixtures.

Recent surveys indicated that only 2% to 5% of growers have installed LED fixtures for supplemental lighting. Therefore, most greenhouses that utilize supplemental lighting still rely on HPS fixtures (Figure 1).

In this article, I will focus on the use and maintenance of HPS fixtures.

Where HPS lighting stands today

Traditionally, high-intensity discharge (HID) fixtures including HPS and metal halide (MH) were used for supplemental lighting as they were 25% to 30% efficient at converting electrical energy into photosynthetically active radiation (PAR).

The mogul-base HPS fixtures had electromagnetic ballasts and bulbs were single-ended (lamp attach to a single socket). About 13 years ago, electronic ballasts became available. These fixtures are typically smaller, cooler, quieter, lighter and best of all, they are 10% to 15% more energy-efficient then their magnetic ballast counter parts. Additionally, the efficiency degrades at a slower rate than with magnetic ballasts.

The efficacy of HPS lamps increased considerably (by >65%) about nine years ago with the introduction of 1,000-watt double-ended (attached to the socket at both ends) fixtures.

Research by Bruce Bugbee at Utah State University has reported that the slow start and steady output of electronic ballasts likely contributes to the increased longevity of double-ended HPS fixtures. These fixtures emit a photosynthetic photon flux (PPF) of around 1,840 µmol·s–1 and have an efficacy between 1.7 and 1.8 J·s^–1.

According to manufacturers, the life expectancy of double-ended HPS bulbs is 10,000 to 15,000 hours to 90% initial light output. Therefore, if your fixtures run 2,000 hours per year, the lamps would need to be replaced in 5 to 7.5 years.

Research findings

In 2008 the Light Research Center (LRC) at the Rensselaer Polytechnic Institute (RPI) reported that most LED horticultural fixtures could not replace HPS fixtures on a one-for-one basis while still maintaining the original PPF. Therefore, approximately three times as many LED fixtures would be needed to provide the same PPF as one HPS fixture.

It is important to remember that each year, the efficacy of LED fixtures increases, and now some light manufacturers do offer LED fixtures that are 650 watts and are a one-for-one replacement for an HPS fixture.

The LRC also found an increase in shading from some LED fixtures compared with HPS due to the size and quantity of the luminaires needed to provide the same PPFD in a greenhouse as an HPS installation. Across the fixtures tested at RPI-LRC, the shading from LEDs reduced sun light in the greenhouse by 13% to 55% compared with a 5% reduction from HPS fixtures.

When to use HPS lamps

Installing, maintaining and operating HPS lamps are a major investment for greenhouse operations. However, most of the up-front costs associated with the fixtures can be calculated and weighed against the potential benefits (ie. yield gains for vegetables or shorter crop turns for young plants).

Even though you have made a large capital investment in these fixtures, there is typically a four-to-six-month period (April to September) depending on your location when the benefit provided by supplemental lighting is minimal and they should be turned off (this is also a great time for maintenance and replacement).

From October until March, the total quantity of light received per day, the daily light integral (DLI), can be a limiting factor in the production of greenhouse crops in northern latitudes. Therefore, the greatest benefit from supplemental lighting occurs at night or during cloudy days from this time period in the north and November to February in the south.

Keep in mind that supplemental lighting requires much higher light intensities than photoperiodic lighting, which needs 2 to 3 µmol·m^–2·s^–1 (10 to 20 foot-candles) and is usually delivered as a night break of four hours from 10 p.m. to 2 a.m. For example, most young plant growers provide supplemental light intensities of 70 to 90 µmol·m^–2·s^–1 at plant height. Much higher intensities of 120 to 200 µmol·m–2·s–1 are recommended for vegetables (Figure 1).

During peak season, young plant production of ornamentals (January and February), DLIs in the greenhouse can range from 2 to 8 mol·m^–2·d^–1 in the north and 6 to 14 mol·m^–2·d^–1 in the south.

Research at Michigan State University indicates that not only do you produce high-quality young plant with supplemental lighting, but more importantly crop timing can be reduced by up to 50% depending on the species when the DLI is maintained between 10 to 12 mol·m^–2·d^–1 for ornamentals and 12 to 15 mol·m^–2·d^–1 for vegetables.

How many hours should an HPS lamp be on in order to achieve the target DLI of 12 to 15 mol·m^–2·d^–1? The amount of time the bulbs are on is just as important as the amount of supplemental instantaneous light they provide. Table 1 gives some examples of how supplemental DLIs ranging from 3 to 19 mol·m^–2·d^–1 may be achieved.

Photo 4b courtesy of PL Light Systems

HPS fixture and lamp maintenance

What is the life expectancy of an HPS bulb? As stated before, under normal operating conditions, replacing bulbs is recommended after 10,000 hours for mogul-base fixtures and 10,000 to 15,000 hours for double-ended fixtures. The number of times that a lamp is turned on or off will also affect the life of the bulb.

In order to get the highest output form your HPS ballast, reflector, and bulbs, routine maintenance and replacement is essential. Some HPS fixture manufacturers recommend cleaning reflectors (luminaries), while other recommend a complete replacement. All recommend replacing bulbs once they have reached their maximum operating life (Figures 2a and 2b).

However, let’s be honest with ourselves: most growers do not do this. I was pleasantly surprised to see an operation in New York that was cleaning all of their HPS reflectors and bulbs (Figure 4). I often see reflectors that are dusty, have water spots or finger prints (Figure 3), or lamps that have burned out or are dim. It is estimated that light output can be reduced by 8 to 15% due to dirty reflectors alone. Therefore, I asked several HPS manufactures for their recommendations on reflector maintenance.

P.L. Light Systems says that if the HPS installation is in a clean environment, or if the reflectors are 1 to 3 years of age, it is possible to clean them with a solution of vinegar and water mixed at a ratio of 1:100. They also advise cleaning your bulbs and reflectors annually for best performance. (Please note that not all manufactures recommend cleaning reflectors. Therefore, you should contact the manufacture of your HPS fixtures for their specific recommendations. Most manufacture can test your reflectors and tell you if it is time to replace them.)

P.L Light System HPS maintenance and cleaning checklist

1. When cleaning reflectors or replacing bulbs, wear eye and hand protection, unplug the HPS fixture from the main power source and allow it to cool for at least 30 minutes to prevent serious burns or injury (Figure 2).
2. While you wait, check cords for damage and replace damaged cords according to the manufacturer’s instruction.
3. Always use cotton gloves to install or remove bulbs as the oils on your hands can create dark spots and reduce lamp efficiency (Figure 2).
4. Carefully remove the reflector. Flush the reflector with distilled water inside and out to remove environmental contaminates (dust, dirt or water spots) (Figure 3).
5. Fill a bucket with a 1:100 vinegar:distilled water solution. Submerge only the reflector for a few seconds (Figure 4).
6. If necessary, carefully use a very soft brush such as a fine finger nail brush to rub off environmental contaminates on the bulb itself. Do not submerge bulbs.
7. Rinse the reflector in a second bucket filled with distilled water to remove cleaning solution (Figure 4).
8. Rinse reflector in third bucket of distilled water to remove any remaining residue. Otherwise hard water spots may remain. If residue is still present repeat steps 5 to 8. If this does not work, it is time to replace the reflector.
9. Allow the reflectors to air dry before reinstalling them on the fixture.
10. For your safety, when cleaning reflectors always maintain the correct ratio and never add other chemicals to the cleaning solution. For more information on correcting problems with HPS Lamps, click here.

The author is an associate professor and controlled environment/floriculture extension specialist in the Department of Horticulture at Michigan State University.

Photos courtesy of AppHarvest

Just a couple of hours outside Louisville, Kentucky, in the small city of Morehead, one of the biggest and most ambitious vertical farm companies in the U.S. is reaping what it sowed four years ago. Morehead only has about 7,000 residents but it’s home to hundreds of thousands of tomato plants that are thriving in a very unique vertical farm at AppHarvest’s first growing facility.

The 60-acre operation, which opened in October, is currently growing beefsteak tomatoes and will soon also be harvesting tomatoes on the vine.

The company’s goal is to provide fresher, healthier, tastier food to Americans while also maintaining high standards of environmental stewardship, employee care and sustainable growth. And in January, AppHarvest’s first crop of beefsteak tomatoes hit retail shelves in stores like Kroger, Publix, Walmart, Food City and Meijer, where they are co-branded with Sunset Grown.

“I’ve long known that the consumer is ready and if you could just give the consumer a better product … the consumer will determine the future for the better,” says David Lee, board member and president.

The flagship AppHarvest facility is expected to produce about 45 million pounds of tomatoes each year from about 720,000 beefsteak and vine tomato plants. “We look forward to every American having the ability to access fresh, healthy, affordable fruits and vegetables,” says Jonathan Webb, founder and CEO.

The Morehead location is ideal for the company’s first facility thanks to abundant rainfall and the fact that shipments can reach 70% of the U.S. in one day’s drive, Webb says. “So to build these facilities in an area where we can collect all that rain water, package it up into a fruit vegetable and send it out to the consumers is critically important in the long-term resiliency of this company.”

The Kentucky location is also important as the company is focused on building “operations and large-scale indoor farms in economically disadvantaged areas of Appalachia,” says Travis Parman, chief communications officer.

Eastern Kentucky was once coal country, but AppHarvest is hoping to transform it into an area known for feeding the U.S. with healthy produce. “Those same men and women that powered the country in the coal mines are working with us here in this facility,” Webb says.

AppHarvest’s crops are grown from naturally bred seeds that were optimized for both flavor and nutrients, which Webb says sets them apart from most tomatoes you’ll find at the grocery store. “Most produce is bred for transportation, so you don’t get the nutrient density that you get with our tomatoes.”

And harvesting produce at peak ripeness and shipping it out quickly means less overall wear and tear on the crops, says Jackie Roberts, chief sustainability officer, noting that 30% to 40% of what we grow never makes it to the grocery store shelves due to supply chain issues.

Roberts predicts there are only 50 to 70 years worth of quality topsoil left for human agriculture. “We need new approaches to growing food that are most resource efficient,” she says. “One other aspect of being resource efficient is the challenge of food waste. When you grow and ship a long way, there’s a lot of loss along that system. Being in Appalachia, being close to 70% of the U.S. population within a day’s drive means less travel time.”

The operation’s tomatoes will be comparable in price to traditionally grown tomatoes, which board member Martha Stewart says is part of what’s exciting about the crops. “I think we all want better for us, for our families, for our friends. We want food that is sustainable, free of chemicals. We want food that tastes really good and that we can afford. Organic food nowadays is so expensive.”

“People can vote with their dollars and vote at the grocery store and decide what [they] want to put on the table,” Webb adds.

Sustainable growing practices

“Our world has a long way to go to rebuilding our food systems,” Webb says. “COVID has highlighted that in many ways but the good things is … the private sector can lead in many of these problems facing our world and we can have a good, tasty product that we can get to every consumer, but we have to use technology quickly to rebuild American farming and the global food system.”

AppHarvest's plants are grown in the soilless substrate rockwool, which consists of fine, granular calcium carbonate. This gives the roots room to grow and absorb water and nutrients efficiently. They then grow about 45 feet high and crews wrap them as they grow. Each day, the produce is harvested and shipped out to grocery store shelves.

The company’s growing practices use 90% less water than traditional field-grown crops and yield 30% more per acre, Webb says. The non-GMO, chemical pesticide-free crops are also grown with 100% recycled rainwater.

To achieve a chemical pesticide-free crop, AppHarvest uses an integrated pest management and biological pest control. “I like to call it integrated pest management 2.0, where we really are focused on using different types of artificial intelligence, the skills of workers and training them to spot pests and disease early,” Roberts says.

She hopes that in addition to being efficient with resources, AppHarvest will reduce the runoff of fertilizers and pesticides into local waterways. “It’s really difficult to prevent,” she says.

Technological advances

AppHarvest prides itself on its high-tech, eco-friendly growing practices. Some of the technology at the Morehead facility includes machine learning, artificial intelligence, robotics and more data-driven agriculture. From industrial software to sensors and lighting and humidity controls, the operation is leveraging tech developments.

“There are a lot of different technologies that are converging right now that will continue to evolve over the next decade,” Webb says.

It all starts with the water, Roberts says, noting that agriculture is consuming 70% to 80% of our ground and surface water. “So we need better solutions. How do we grow more food with less water?”

AppHarvest uses a closed loop system that captures rain water on the roof and stores it in a retention pond the size of 70 Olympic swimming pools. The water is then filtered through sand and UV light treatments before it heads into the greenhouse for irrigation.

The water is constantly monitored for the nutrients vital to plant growth and nano bubbles are added to increase oxygen to the water. This allows the plants to better absorb nutrients in the water. “That makes a stronger plant that’s more disease resistant and it’s also one where we can build up nutrition,” Roberts says.

Unlike most greenhouse operations, AppHarvest has undergone an aggressive series of fundraising and financing to raise capital for its Morehead location and other planned facilities. It all began in 2019, when the company raised $520,000 through investment platform Harvest Returns.

On Feb. 1, the company completed its business combination with Novus Capital Corp., a publicly traded special purpose acquisition company, and started trading on the Nasdaq under new ticker symbols APPH and APPHW. The company's stock opened at $35.69 and by the afternoon, shares soared 44%. As a result, the Nasdaq temporarily halted trading due to the volatility. Trading resumed soon after and closed the day at $35.85. As of Feb. 15, the stock was trading at $33.26.

The company announced in September 2020 that it would combine with Novus Capital in order to go public. It initially sold for $10 a share with a $1 billion pro forma equity value.

As a result of the initial public offering, AppHarvest received about $475 million of gross proceeds, including $375 million from the common stock PIPE anchored by investors including Fidelity, Inclusive Capital and Novus Capital. The company says this provides $435 million in unrestricted cash, which will be used to fund operations, including building additional farms, supporting growth and other general corporate purposes.

Webb hopes that the private sector will help lead the charge to solve the world’s food issues. The company is not only publicly traded, but it’s one of few public Certified B Corporations listed. As a Certified B Corp, AppHarvest is legally required to consider the impact of their decisions on their workers, customers, suppliers, the community and the environment.

“Our take is over the next decade, every company — Fortune 500 to startups — every company in the world needs to be working toward these same goals that we’re talking about,” Webb says. “And if you’re not, you as a CEO should no longer be looking for quarterly earning calls and that’s it.”

As Webb says, it’s all a part of creating value among everyone, including the broader stakeholders, the environment, the community, the consumers — everyone the company impacts. “It’s harder on us as a company, but it’s the right thing to do. And at the end, for the investor, it’s a better return in the long run because you’re making sure your company is viable, relevant and resilient for decades to come.”

What’s next?

While the company is focused on its Morehead location, it is also planning aggressive growth, building a 60-acre facility outside of Richmond, Kentucky, and a 15-acre leafy greens operation in Berea, Kentucky.

The company hopes to have a total of 12 farms in the central Appalachian region by the end of 2025. “And that means investment for important, long-term oriented investors. It means supply chain sophistication. It means looking eventually globally to solve the global problem, but today we’re focused on Appalachia,” Lee says.

Stewart believes the tomatoes from AppHarvest could go beyond fresh produce to have a place in prepared foods like sauces and soups as well. “We need to be making our prepared foods with this kind of produce as well as serving this kind of fresh produce to the customer,” she says.

With spring coming, greenhouses are bustling as they fill with annual and perennial landscape plants for the coming summer. While flowering bedding and garden plants are the most valuable sector of the U.S. greenhouse industry, there are also opportunities for producing these flowering plants — as an edible!

Edible flowers are increasing in popularity as they add not only a colorful appearance, but also a range in flavors from sweet to tart, to a finished dish. Though there is a lack of information regarding hydroponic production of edible flowers, this month’s column will review some of the most important points to consider.

What you need to know to get started

First and foremost, start by selecting the edible flower species you would like to grow.

Some of the most popular edible flower species include familiar annuals such as pansy (Viola × wittrockiana), viola (Viola cornuta), snapdragon (Antirrhinum majus), nasturtium (Tropaeolum majus), wax (Begonia × semperflorens-cultorum) and tuberous (Begonia × tuberhybrida) begonias, African (Tagetes erecta) and French (Tagetes patula) marigolds, and dianthus (Dianthus chinensis). There are also perennial plants with edible flowers, such as hibiscus (Hibiscus rosa-sinensis), peony (Paeonia lactiflora), rose (Rosa spp.), and lilac (Syringa vulgaris).

When comparing the production of flowering plants for food as opposed to flowers, one of the most noticeable differences you will likely encounter is in pest control. Flowering plants grown for ornamental use are able to be treated with wide array of pesticides for controlling insects, mites, fungi and bacteria.

However, when grown for human consumption, the vast majority of the same pesticides used for ornamental production are unsuitable and not labeled for use on edible crops. Often the best way to make sure your crops are safe (i.e. not containing pesticide residues over the allowable thresholds) is to grow your own transplants as opposed to buying them. This will ensure you are using plant material that has never been treated with pesticides and will be safe for human consumption.

Additionally, nearly all commercial plugs are going to be grown in plug trays filled with a loose peat-based germination mix. For hydroponic production, you will want your seedlings grown in an inorganic substrate suited for hydroponic production (rockwool or phenolic foam), or an organic substrate (peat or coconut coir) with a binder that holds together loose substrate. This will help ensure your success.

Which hydroponic system is right for me?

The most suitable hydroponic systems for edible flowers are those that are used for the leafy green and culinary herb production — most notably nutrient-film technique (NFT) and deep-flow technique (DFT) or raft systems.

While both NFT and DFT can be successfully used to grow flowering plants, NFT systems are usually well-suited to the recurrent harvest of flowers compared to DFT, as NFT channels are typically placed at waist height and flowers can be harvested without bending over, in contrast to DFT systems which are usually installed at ground level. The systems favored for growing fruiting vines, like slab/bag culture or Dutch buckets, should be avoided.

Manage the environment as always

The greenhouse environment — light, temperature and carbon dioxide — for hydroponic edible flower production is one area where producers can draw from existing production literature for flower crop production in containers with substrate.

Simply because flowers are grown hydroponically does not in any way fundamentally change environmental production requirements. For example, cool-growing annuals such as pansy, viola and snapdragon should still be grown using cool air temperatures.

Fertilization will change, too

Unlike the greenhouse environment, switching from a soilless substrate to hydroponic water-culture systems will require a bit of grower trial-and-error with respect to formulating a mineral nutrient plan.

While you can find fertilizer requirements for most edible flower species, they are going to be for soilless substrate and not for hydroponic systems. However, recommended electrical conductivities (EC) for substrate culture, as well as the classification of various crop varieties by their fertilizer requirements (i.e. light, moderate, and heavy-feeding plants), gives a grower new to growing in water a good indication of nutrient requirements. Similarly, substrate pH recommendations can be used as guidelines for determining the optimal nutrient solution pH. A good range to start is a nutrient solution with a pH of 5.5 to 6.0 and an EC around 1.5 mS/cm, with further refinements made based on crop response. My takeaway for new edible flower hydroponic growers? Jump in 2 feet first and take the plunge.

Growing edible flowers hydroponically provides an opportunity for any produce grower to add an exciting new crop and expand their product portfolio, which is exactly what growers should be looking at to accomplish in the post-pandemic world. And, although there are currently few resources specifically catered to hydroponic edible flower production, the existing body of knowledge for growing the same species in containers with substrate can be used to get your crop off to a great start.

The author is an associate professor of horticulture at Iowa State University. Reach him at ccurrey@iastate.edu

PHOTO © smspsy | ADOBE STOCK

I heard a rumor that chefs have gotten a bit tired of microgreens and are dialing back on their orders from growers. But that is not what my chef friends here in Dallas, Texas, are telling me. Additionally, I certainly do not see interest in microgreens declining with home gardeners. As far as they are all concerned, microgreens are in — way in.

The massive surge in pandemic gardening, in fact, has brought microgreens back front and center in the minds of home growers. Every day I see another article pop up about microgreens from a bevy of health and wellness websites to gardening blogs and social media channels.

In fact, I must admit that all the exposure to microgreens marketing lately has pushed me back into the growing game. It has been a couple of years since I constantly grew microgreens, but repeated exposure lately has me back at it. No doubt, the consciousness around growing microgreens at home will no doubt influence increased demand at the grocery store and when dining or taking out.

Grow healthy

Health and wellness will be at the forefront of consumer consciousness in an even bigger way in 2021 and beyond. The pandemic has made healthy eating and immune system support a top priority for many of us right now. Additionally, combating the effects of too much screen time and home computer work are at the top of everyone’s to-do list.

With immense stressors on both our bodies and minds, easily incorporating more healthy fresh vegetables into our diets is a must.

In fact, I would say that most Americans have gotten a big wakeup call when it comes to how we are — or are not — taking care of ourselves when it comes to what we put in our mouths. We are all looking for simple and easy ways to improve our diets and nutrition. What could be easier than throwing a handful of microgreens into our soup or on our sandwich?

Big nutrition that stacks up in such a tiny package is a powerful tool both for the home consumer and growers. With microgreens of veggies such as cilantro, red cabbage and radish containing up to 40 times higher levels of nutrients than their mature counterparts, there is no denying a little goes a long way with microgreens.

Beyond touting the benefits of microgreens as a boost of color and flavor for diners, growers and chefs alike should capitalize on the real authentic health benefits these tiny veggies can add to every plate.

Elevated dining

As far as trends go, creating an “elevated” home dining experience is also big with consumers right now. Home cooks are looking for ways they can elevate not only the nutrition of the food they make, but also their dishes sensory experience. That is where the added boosts of color and flavor provided by microgreens come in handy.

When I checked in with some of my go-to culinary experts, they assured me microgreens are still on the menu. Fresh Origins Micro Fines Herbs Mix and Micro Intensity Mix are a couple of popular favorites, specifically for each product’s bright color value.

I’m told there’s also been a shift in which microgreens culinary professionals favor, from standard clamshells of mixed microgreens to a single species of microgreen with a more monochromatic look.

Beyond mixes, red veined sorrel, cilantro and arugula microgreens top the list of popular species. There are also a few more interesting microgreens that are favored, including sweet alyssum, micro nasturtium, Mexican marigold and pea tendrils. Check out “The Art of Plating” website for some visual inspiration (here).

Grow local

When I asked my local Dallas chef friends where they are getting their specialty microgreens, the focus was on local sourcing. The fresher and more local the microgreens, the better. I was pointed to Profound Foods, a Dallas-Fort Worth “food hub” that provides an online marketplace for locally grown and produced foods. They have a seasonally rotating selection of microgreens in addition to many other foods (here).

Profound Foods works to connect local farmers with local chefs to meet the growing demand for sustainable food. They also allow home consumers to order their produce and other fresh foods for home delivery. You must leave a cooler on your doorstep and your fresh produce is dropped off in the cooler. Unfortunately, it does not look like my zip code has made it into their home delivery zone yet, but anyone can register to be a pick-up customer at specified locations around the Metroplex.

I think this is an excellent model that combines aspects of conventional wholesale produce sourcing for local chefs and restaurants, and the farmers market platform for home consumers. The hub is a solution to both connecting chefs and consumers to fresh local produce, while at the same time addressing the strains of in-person shopping created by the pandemic. It’s a great opportunity for local farmers to deepen their community reach.

Ultimately, I would say the outlook for microgreens in 2021 is pretty tasty. Make sure you are leveraging the big boom in consumer consciousness when it comes to the health benefits of your microgreens, and do not forget to show consumers how they can use microgreens to enhance and elevate their at-home eating experiences.