Today, more than two-thirds of new greenhouse construction is covered with film plastic. Besides the obvious advantages of low-cost, low taxes, ease of covering, four year life and additives such as anti-drip and light diffusion, there are other properties that should be considered when purchasing the material.
Manufactures have worked hard to provide a material that will give good service, high light transmission and properties that improve plant production. Most greenhouse polyethylene film is manufactured as a coextrusion of three or more layers with different polymers and additives. Each of these layers contributes to the quality of the film by adding tear and puncture resistance, high light transmission, IR retention, UV blocking, dust control and color pigments.
The following reviews some of these often overlooked properties that could influence your purchase decision.
A plastic film is considered an infrared film (IR) if less than 25% of the heat generated within the greenhouse is allowed to escape. The lower the percentage, the lower the winter heating bill. Regular greenhouse grade polyethylene film allows 30% to 60% of the IR heat to escape.
Plastic manufacturers have found that mineral based additives, such as ethyl vinyl acetate (EVA), calcined kaolin clay or synthetic aluminum silicate can reduce the radiation loss. This material is usually added as one of the inner layers in the copolymer.
These additives may reduce light transmittance slightly but they also diffuse the light spreading it evenly inside the greenhouse reducing shadows and allowing more light to reach lower into the canopy. It also helps to average out leaf temperatures at the top of the plant canopy reducing the amount of shading needed.
Often building officials question a grower applying for a building permit as to the flammability of the film plastic. Section 3102.3 of the International Building Code states that “Plastic less than 20 mil thickness or located less than 30 feet above the floor as used in greenhouses where occupancy by the general public is not authorized is not required to meet the fire propagation performance criteria of NFPA 701 (National Fire Protection Association)”.
Low density polyethylene plastic is an oil-based product with a high heat value of about 20,000 Btu/pound. It will burn if in contact with an external flame but does not maintain a flame by itself for very long. The additives used in copolymers could affect this some so obtaining the test results from the manufacturer may be necessary. Also copolymer film may not get building official approval for retail greenhouses.
These absorb or reflect specific wavelengths of light. They can enhance plant growth, suppress insects and diseases and affect flower development. Red films such as Dupont IR and Smartlite Red film reduce PAR light and create a shading effect. They have also been shown to improve rose yield and quality.
Plastic film manufacturers have developed disease control films that absorb UV radiation in the 340 to 390 nm wavelengths. These have been found to reduce the population of insects such as whiteflies, thrips miners and aphids. The material can also control the spread of certain diseases such as botrytis.
As bees need UV to navigate, if you are using bees to pollinate plants in the greenhouse, purchasing a film that allows some of the UV part of the light energy spectrum to pass through may be important.
Off-gassing from film
Recent research by Dr Sarah-Jeanne Royer at the University of Hawaii in Manoa has found that LDPE film produces methane and ethylene gas when exposed to sunlight. In large poly covered ranges the amount of gas produced may be significant. As these gases can affect plant growth, additional research is needed to determine the level that may have an effect.
John is an agricultural engineer, an emeritus extension professor at the University of Connecticut and a regular contributor to Greenhouse Management. He is an author, consultant and certified technical service provider doing greenhouse energy audits for USDA grant programs in New England. email@example.com
As her last name suggests, Diane Green was destined to end up in the greenhouse industry. Yet, that wasn’t the original plan when she graduated from Kent State University with a degree in vocational home economics, or even when she started working in DeHoff’s flower shop 43 years ago.
Initially, Green was going be a high school home economics teacher, but after a year of looking for jobs while substitute teaching, she decided to apply at DeHoff’s in Alliance, Ohio, where her brother worked. She started out wrapping Easter lilies and transplanting seedlings. By summer, she was making floral arrangements, and before long, she was managing the whole flower shop.
Green focused solely on flowers for about 20 years, until DeHoff’s head grower left the greenhouse division. Seeing an opportunity to improve the production of plants she was selling in the shop, Green took on the added responsibilities of growing. Now, in her dual role as manager of both the flower shop and the greenhouse, Green oversees the entire product lifecycle to produce beautiful plants for DeHoff’s customers.
Striking a balance
Although there is some overlap between her two roles, Green works long hours managing both the flower shop and the greenhouse operation at DeHoff’s.
“One of my biggest challenges is finding time to get everything done,” says Green, who relies on her team for help. In the flower shop, she’s assisted by two retail employees as well as an office manager. In the greenhouse, depending on the season, she has three or four “excellent greenhouse girls who take care of the work,” such as spraying, pinching, watering, and transplanting.
Green spends most of her day in the flower shop, serving customers and designing floral arrangements, but most days begin and end in the greenhouse. First thing in the morning, she meets with her growing team to “get the girls going with what they need to do that day,” she says. Green leaves written instructions to keep her team on track while she’s in the flower shop, and stops in at least three or four times a day to check their progress.
The greenhouse produces plant material to supply DeHoff’s other divisions, which include the flower shop, a garden center, and a full-service landscaping business (hence the official name, DeHoff’s FGL Inc., which stands for Flowers, Greenhouse and Landscaping). With 29,000 square feet of space, Green grows everything from poinsettias and Easter lilies to annuals, perennials, houseplants, and succulents.
“We’re so diverse,” she says, “which means we don’t have a whole greenhouse full of marigolds. I’m raising marigolds with petunias and geraniums, and they all have different growing requirements.”
Striking the balance to successfully grow a diverse crop mix requires some creativity — which, as a floral designer, is one of Green’s defining characteristics.
Creative time savers
To be effective at managing both divisions, Green has to be efficient with her time.
“One of my primary goals when I took over the greenhouse was to figure out how to grow an excellent crop without spending too much time doing it,” she says.
For example, Green doesn’t have time to spray six applications of pesticide on every Easter lily crop. Instead, she looks for time-saving tricks and alternative solutions —using plants and even bugs to her benefit.
“I’m trying to do more with bio-organic controls, so we’ve been using nematodes,” Green says. “That saves me some time, because if I can keep (pest populations) down with a simple release of nematodes, then I don’t have to spray.”
“When I walk out in the evening to close the greenhouse, it’s like going out to my own big garden to relax. It’s like my baby ... I like ... being creative with plants." —Diane green
So far, Green has had “fairly good success” controlling harmful pests with nematodes. Now, she’s also experimenting with some plant-based alternatives for pest control, like “using lemony-scented plants as bug repellants.”
“Last year, I put them down through the middle of my petunias, and I had pretty good success keeping the aphids off,” she says. “One year I tried raising banker plants (which provide supplemental food for beneficial insects) to keep it more natural and save some time. If they’re taking care of it, then I don’t have to work so hard.”
Green believes that her dual role at DeHoff’s puts her in a prime position to meet customers’ needs by focusing on quality throughout the plant’s lifecycle. Since she’s responsible for everything from crop planning and growing decisions to making floral arrangements, the final product is literally in her hands.
“When I walk out there in the evening to close the greenhouse, it’s like going out to my own big garden to relax. It’s like my baby,” Green says. “I like making pretty things and being creative with plants.”
And she doesn’t plan to stop anytime soon. “Maybe someday I’ll retire,” says Green, 68. “And then maybe I can just go back to watering and transplanting, and then I’ll have gone full circle, right back to where I started from.”
The author is a freelance writer based in Cleveland.
The past year has taken many businesses in the green industry to extreme highs and lows. While the pandemic stimulated a huge influx of new customers into the hobby of gardening, COVID strains on supply and freight have hurt many businesses’ ability to meet increased demand. Combine increased demand, labor pressure, and the need to quickly invest in and implement updated technology for online sales, and you have a robust recipe for chaos.
Many retailers have been left wondering how they will satisfy end-consumer needs and still capitalize on the garden surge; and if and how their growers are pivoting to provide alternatives? It is going to be more important than ever that growers and retailers work together closely to provide good plant alternatives and manage customer expectations with proactive marketing.
Setting the stage
We were already facing key plant shortages going into the 2021 spring season. Big trees and large shrub supply have still been lean since the 2008 recession. But the severe storms and record deep freeze events across the South pushed supply concerns and realities into the critical zone.
Never have I ever seen such a brown spring here in Dallas, where I make my home. Many large established foundation shrubs and small trees were either killed or killed back to the snowline or root zone. Damage to larger trees such as live oaks is yet to be fully realized.
While many are heading into the busiest part of the retailer’s spring season in May, the southern half of the country is typically winding down its spring surge. Here, spring usually starts around mid-February. That spring start was delayed a bit by the deep freezes we experienced, but it will not stop intense heat from coming on by May. By Mid-May we begin to emerge from the tail-end of spring and are onto the typically more moderate summer sales season. If you have any industry friends in southern states, who are wrapping up their spring this month, it might not be a bad idea to check in with them for a pulse on plant demand and successful substitutions.
A mixed bag so far
I checked in with one of my clients, Doug Arnold, who owns both Trees USA and Plants of Texas. The grower and re-wholesaler and retail garden center operate out of Lindale and Tyler, Texas, respectively.
In Arnold’s 41 years in the nursery business, he says he has never seen business this good or this bad at the same time. As has already been the case for the last decade, Arnold affirms that large tree and shrub inventory were already stretched in terms of consumer demand. “Fast forward to the spring of 2020 (the COVID year) and everything else kicked in with unprecedented demand in color, tropical foliage, all edibles and trees,” he says.
Consider partnering with nearby businesses to bundle your flowers and plants with other local products.
After being hit with heavy freeze damage in February, customers began pouring into Plants of Texas’ retail outlets to replace all their dead plant material, with shrubs making up a big percentage of replacements.
Arnold notes that many color growers in Texas, not to mention shrub growers, were also hit hard with structural damage from the extreme winter weather. In addition to plant losses, the structural damage left them unable to provide any stock during the first quarter. Many of these growers have now already exhausted their second quarter inventory, further complicating supply issues for plants across many categories.
“With the onset of COVID we saw a dramatic shift in customer demands at the retail level,” Arnold says. “The lockdowns had people shopping in numbers we had not experienced before. The landscape supply portion of our business also continued to hit record high numbers throughout the summer into the fall in 2020.”While business is great right now, Arnold admits limited plant supply is going to start restricting their ability to maintain current levels of business. He says huge increases in freight costs and a limited supply of trucks is an additional problem. All said, they are doing their best to keep up with demand as well as try to catch up on production. Arnold cautions that “this definitely has been one of those years where you needed to have strong relationships with your suppliers.”
A potential solution
So, what do you do when you simply cannot get the plants you need to meet customer demand? Try shifting the marketing to what you do have and better manage your messaging. If you know you are short on commodities, be ready to educate your retailers on what you will have and how to offer substitutes to customers.
Here in Texas, I am advising homeowners to be patient when it comes to replacing shrubs and trees. They may need to get on a waitlist or place an order for future fulfillment. Take the opportunity with some new “holes” in your landscape to make better plant choices and focus on pollinator and habitat health as well as water conservation.
If you have native or better-adapted plants to offer in place of limited-supply commodity cultivars, now’s the perfect time to push them. And of course, if you sell edibles and can maintain good inventory, there is no better time to push stock for vegetable and herb gardening in place of limited seasonal color. A 2021 foodscaping push perhaps?
Most importantly, I will echo Arnold’s advice and say that in times like these, it all comes down to relationships. If you have good ones, you will probably stay better stocked. If not, well, there is no better time than now to turn over a new leaf.
Leslie (CPH) owns Halleck Horticultural, LLC, through which she provides horticultural consulting, business and marketing strategy, product development and branding, and content creation for green industry companies. lesliehalleck.com
Cut flowers were the crop that led to the United States’ greenhouse industry. While cuts were traditionally grown in mineral (“field”) soils in the ground or in ground beds containing field soil under protection, most commercial cut flower production in greenhouses occurs in hydroponic or soilless production systems..
Let’s review some of the hydroponic and soilless systems available for producing cut flowers.
One popular system for growing cut flowers in greenhouses should be familiar to grower producing tomatoes hydroponically. While slabs of rockwool are a popular choice for many vining and fruiting vegetable crops, they are also well-suited for hydroponic cut flower production. Most slabs are around 1-yard (or 1-meter) lengths, different widths and depths available to accommodate the needs of different crops and their root systems. A primary reason why rockwool is so well-suited for long-term cut flower crops (roses, for example) is the long lifespan of the substrate. Since rockwool is an inert, inorganic material, it will maintain its physical integrity for a long time which, in turn, maintains the desirable physical properties for root systems throughout the long cropping cycle characteristic of many cut flower species.
Individual containers filled with loose-fill substrate can also be used to produce cut flower crops. Suspended at heights comfortable for working canopies and harvesting, containers are filled with soilless substrate plants are transplanted into and grown on continuously throughout production. Coconut coir, as seen in Fig. 1, is a popular choice for use as a loose-fill substrate in containers. Unlike rockwool, coir is an organic substrate; but, like rockwool, coir can maintain physical properties longer than other organic components such as sphagnum peat moss. Coconut coir has a high lignin content which, in turn, resists breakdown by microbes and subsequent decomposition. Other substrate components can be amenable to use in container culture, if they are well-matched to the crop time. For instance, sand or perlite can be used in containers as a growing substrate .
Bulb crate & soilless in-ground production
“One person’s trash is another person’s treasure.” That well-worn statement is very fitting for bulb crates. Bulb crates can form the basis for a simple soilless cut flower production system. By filling bulb crates with soilless growing substrate such a traditional peat-perlite mix, planting them, Furthermore, the planted crates can be arranged in the greenhouse in “beds” and supports placed above them.
This simple system also allows for flexibility between different crops. Depending on the length of cropping cycles, the substrate may be able to be pasteurized and reused if the organic material has not broken down too much, thus maintaining its physical properties.
The focus of this article is on hydroponic or soilless methods of cut flower production, so it may seem a bit out-of-place to discuss in-ground production of cut flowers as hydroponic. However, when the “soil” is an inert material such as sand (Fig. 2), the system is functionally a hydroponic one - where the substrate has little-to-no-influence on the chemical properties of the root zone.
Regardless of which of the systems mentioned above are used, they are all similar with respect to irrigation. The vast majority of systems use some type of drip irrigation system, where the nutrient solution is delivered to the surface of the growing substrate. Overhead irrigation is roundly avoided with greenhouse-grown cut flowers for a variety of reasons, from maintaining flower quality to avoiding diseases. For several of the cut flower production systems discussed in this article, micro tubing and drip stakes are used to irrigate plants, while for other systems turbulent twin-wall tubing or “drip tape” can be run down plantings.
Like hydroponic nutrient solutions for food crops, cut flowers commonly have at least two different nutrient stock tanks:the “A” and “B” tanks. This allows high concentrations of nutrients including calcium to be provided to plants, without risking precipitation of calcium with sulfate as insoluble calcium sulfate.
Cut flower production has evolved with the greenhouse technologies they helped spur development of in the U.S. Across the spectrum of production systems available, many cut flowers grown in greenhouses employ hydroponic systems of one type or another, as this article has demonstrated. Perhaps one of these systems, or a variation on it, will prove useful in your greenhouse.
Christopher is an associate professor of horticulture in the Department of Horticulture at Iowa State University. firstname.lastname@example.org