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Landscape Prescriptions by MD Ornamental hot peppers (Capsicum sp.) and their exciting use throughout the landscape are finally entering the lexicon of most gardeners. The contributions of colorful fruits in white, cream, yellow, orange, red, purple and black are significant, particularly later in the season as the fruits ripen up over the hot summer months. Many varieties will go through a colorful transition with multiple colors of fruiting on the same plant.

The ornamental impact of these increasingly vivid fruits can rival any bedding plant late in summer. Most ornamental hot peppers have some common traits which include shorter stature, the fruits are frequently staged and held above the foliage and, of course, the colorful fruiting show that is exceptional until the hardest of frost.

Why ornamental peppers?

It is important to note that while “ornamental hot peppers” are edible, they are not bred for culinary value and frequently lack the depth of taste that many traditional hot pepper varieties provide in terms of a flavor profile. Most ornamental hot peppers have muted taste, but a whole lot of heat.

With limited to no culinary history, most of the ornamental hot peppers haven’t been researched for Scoville heat units (SHU) that reflect the heat of these fruits. Be wary of the unknown. Keep in mind that some people have severe allergic reactions in relation to eating, handling or even being near hot peppers in the garden.

It is important to also note that some of our most common hot peppers (i.e. ‘Jalapeno’, ‘Tabasco’, ‘Scotch Bonnet’, etc.) are also beautiful when the fruits transition to more intense color as they ripen.

A feature of merit that is often overlooked in the category of ornamental hot peppers is the contribution of ornamental foliage. As with any type of plant, having multiple features of interest diversifies the ornamental contributions of the plant, adds additional or lengthier interest and in the case of ornamental foliage, may become the primary feature of interest.

With ornamental hot peppers becoming so popular in bedding schemes, container arrangements, later season displays and simply for general use, the contribution of ornamental foliage broadens the opportunity for using these plants in showy and imaginative combinations.

Classification and deployment

Ornamental foliage for these hot peppers falls into some basic categories based on my observations. There are those that have a white to cream variegation on the leaves. Some varieties will have a variegation that includes hints of violet and purple. Some of my personal favorite selections have near black foliage throughout the growing season. The last category are those selections that have foliage that deepens to a black coloration in late summer at the time when the fruiting show is at peak.

We’ll examine some selections in each of those categories further in the article.

In terms of using these plants in the landscape, certainly evaluating the merit of the colorful fruits in the landscape is a primary consideration. While most traditional ornamental hot peppers aren’t offering much interest in terms of fruit coloration until later in the summer, those with colorful foliage are immediate contributors to the composition.

For example, those selections with near black foliage offer a depth of richness even prior to the fruiting which then offers interest while using that same foliage as a backdrop or foil for the ripening fruits. Selections with variegated foliage will attract the eye over the entire growing season and become a nice backdrop for colorful, ripening fruits. Ornamental hot peppers at peak fruit coloration are becoming hot sellers in late summer as they not only provide instant, vivid color but limitless potential as late season “filler” in garden beds and later season container arrangements.

Ornamental hot peppers in general really need full sun locations and will thrive in the bed, border or container. Drainage is vital and they don’t mind rich or amended soils. Some fertilization may be in order, particularly for container specimens and while these peppers all have some degree of drought tolerance and like it hot, don’t let them dry out. Keep up with a watering regime that accommodates a moist and well-drained situation.

Planting any sort of pepper out in the garden shouldn’t occur until the soil temperatures are minimally 70°F and the evening temperatures are nearing 60°F on average. There is danger in planting peppers too early with damp and cool soils offering little incentive for the peppers to actively establish or grow. If sowing seeds of select varieties, target your sowing 10-12 weeks in advance of the last frost date in your area and keep seedlings happy and safe until planting in a warming soil in their final destination.

And keep in mind that peppers of all kinds have a wide range of potential insect and disease issues that can be addressed as needed, although healthy specimens will be the least likely to show evidence of being compromised and needing that additional TLC.

White/cream variegated ornamental hot peppers

I’m personally a big fan of variegation in any type of plant. While we might be selecting certain plants for interesting form, flowers, fall color, etc., having the additional contribution of variegation just adds to the extended show. That’s certainly the case with variegated ornamental hot peppers as well.

Some great selections with the white/cream contribution include Uchu (9 inches), ‘Sparkler’ (18 inches) and the classic selection ‘Fish’ (24 inches). It’s interesting to note that in some instances, the variegation extends to the fruits as well. This is the case with both ‘Sparkler’ and ‘Fish’. This variegation, while varying in prominence, is still visible throughout the color transition of the fruits. All of these selections have a fruiting transition from cream to yellow, orange and finally red with multiple colors on display depending on the maturity of separate fruits.

If you are interested in variegated sweet pepper selections, look for ‘Confetti’ or ‘Candy Cane Red’ which are both mini-bell selections with impressive variegation of foliage and fruits.

Violet/purple variegated ornamental hot peppers

For simply the sheer value of foliage contribution, these selections are excellent. I’ve grown ‘Purple Flash’ ornamental hot pepper for over 20 years and never tire of the reliable, variable, purple variegation seen throughout the foliage with no two leaves being identical.

Reaching 15 inches in height, this is truly a bedding plant known for prominent foliage as the fruits are jet-black, quite small and truly a secondary asset to the foliage.

The variety ‘Tricolor Variegata’ (18 inches) is another classic selection with similar splashes of purple and cream over the foliage. However, the thin, long fruits of this selection become more prominent as they transition from deep purple to bright red.

Dark foliage ornamental hot peppers

My personal favorite ornamental hot pepper is the variety ‘Black Pearl’ which displays near-black foliage in full sun. The fruits emerge a glossy black and age to a bright red late in the season. This 2006 All-America Selections (AAS) winner reaches 24 inches in height and offers a rich, bold color with and without the fruiting contribution.

Additional AAS winners with black foliage and similar impact include ‘Black Olive’ (18 inches), ‘Black Hawk’ (12 inches) and Onyx Red (9 inches). All of these selections have the same colorful fruit transition from glossy black to bright red.

The variety ‘Count Dracula’ (16 inches) was another favorite with a black, matte-finish foliage contribution with short, elongated fruiting that also goes from black to red. Full sun is absolutely necessary to get the deepest black foliage coloration on all of these selections. Emerging foliage, while having hints of green, will all deepen and darken in full sun during the hot summer months.

Ornamental hot peppers with darkening foliage

This might seem like an odd category when considering the topic of ornamental foliage on these hot pepper selections. However, these two varieties in particular have an interesting foliage transformation from dark green with maroon overtones in the summer to a very deep black when the fruits are aging to their best coloration. Seek out both ‘Explosive Ember’ (12 inches) and ‘Midnight Fire’ (14 inches) for this feature along with fruits aging from glossy purple to a deep red with many colors in between that transitioning gradation of coloration. ‘Explosive Ember’ actually has a “cross-over” audience for culinary use with the peppers having decent flavor and heat of a cayenne pepper.

As the lead grower at Hoffman Nursery (Rougemont, North Carolina) – an industry leader and 30-plus year grower of greenhouse ornamental and native grasses (slogan: We Grow Great Grasses!) – Bill Hall knows all-too-well the difficulties that can arise in getting some of the varieties to root prior to shipment.

Hall and his production team typically receive grass varieties in large clumps, which they then break down into smaller plots that they call divisions.

“We’ll pot those divisions into liner pots, and then we’ll typically put them in our houses under our misting systems for about 14 days,” Hall says.

Misting involves lightly applying recycled irrigation water atop of the divisions multiple times throughout the day. The grasses should respond accordingly with vegetative growth increases within about two weeks, according to Hall.

“We should see them start to root in about 10 to 14 days, and typically by day 14 they're off of the mist and they are ready to go,” he adds.

The specific timing around your preferred rooting is another important aspect to consider. If you are hoping to start the production cycle early and overwinter them in cold frames until shipping season hits – which is what Hoffman does – you’ll want to get the cycle going in the late fall or early winter. In that case, you will want these activities to occur inside a heated structure and keep your ambient temperatures above 60° F to encourage root development.

“This time of year, it’s warm enough here in North Carolina that we can do it outside and still have success,” he adds.

Trending varieties, grasses for backup?

Hall confirmed that the rumors this spring are indeed true: greenhouse and nursery operations of all sizes are seeing constrained young plant supplies as we turned the page from early to late-spring.

Many brave prognosticators have forecast that operations will likely be forced to grow something, anything, beyond their usual crop mixes to keep plants available for their customers into mid-to-late-summer. Many thought perhaps ornamental and native grasses would fill the hole left by the expected flower, tree, and shrub shortages.

Not so fast, according to Hall.

“We’re basically sold out across the board right now on everything in our houses,” Hall explains. “That’s across the board for both warm and cold season grasses. We’re just completely sold out.”

The specific ornamental grasses that Hall is seeing increased consumer and landscaper demand on are Carex varieties, which are sedge grasses, and include such notables as Carex Bunny Blue (bit.ly/CarexHobb), Carex Everest (bit.ly/CarexEverest), and Carex ‘Everillo’ (bit.ly/CarexEverillo).

“Unfortunately, the biggest issue right now is the shortage of supply that everyone is encountering on plant material, and that will exist for the grasses as well. Believe me, we know this because we’ve been looking for ourselves, too.”

Photos courtesy of Leider Greenhouses

Supplemental lighting can be as unique as the crops a greenhouse owner grows. Greenhouse Management magazine spoke with Elizabeth Leider, assistant production manager of Leider Greenhouses in Buffalo Grove, Illinois, to get a glimpse into how one greenhouse operation tailors its lighting to achieve better production results.

Greenhouse Management: What crops do you grow and in what type of greenhouses?

Elizabeth Leider (EL): We are a wholesale flower grower. We grow spring and summer annuals, and we also grow a few perennials. Most of the annuals we grow are used for container gardening or as bedding plants. In the summer, we grow hardy mums and we grow poinsettias for the Christmas season. We also grow Easter lilies, hydrangeas, and a few indoor-blooming plants. Our facility was built in 1963 and we’ve expanded onto it multiple times, so we have glass greenhouses, double polycarbonate greenhouses and polyethylene greenhouses.

GM: What types of supplemental lighting do you use and on which crops?

EL: Originally, we only used HPS. I would say in the last eight years we’ve started investing in LED. The HPS lights are primarily still used for our indoor bloomers and for propagation. We use them to either extend the day length or just increase the amount of light in the greenhouses.

The LEDs we primarily use for propagation. We also use them to further speed up some of our crops. For instance, we noticed just this year that the zinnias we put under LED lights were about a week ahead of those that weren’t.

The LED lights are newer toplighting. I believe the color spectrum is a red spectrum, but they’ve really improved it recently, so it’s not as harsh on your eyes. It’s got a white quality to it. So, we have some older lights and we have some newer ones as well. Our older lights are definitely pinker, harsher, and the newer ones are a lot easier to work under.

GM: Do you have different lighting setups based on the type of greenhouse?

EL: In general, glass lets in more UV light, whereas the polycarbonate filters it out a little bit more. We don’t have any LEDs in our glass houses. Those are very traditional-style houses, and we just use them for specific crops. Easter lilies, for example, really like the glass houses and won’t get enough light if you put them in a polycarbonate house.

Our propagation houses are, I believe, double polycarbonate. All of our greenhouses were built to grow indoor-blooming plants. They weren’t built to grow annuals, so we really need the supplemental light to help the annuals beef up.

GM: Can you talk more about why you use supplemental lighting and how important it is to the success of your crops?

EL: In regard to propagation, it definitely increases the rooting speed for a lot of the unrooted cuttings that we propagate for most crops. And supplemental lighting in general, it’s a more uniform distribution of light because some of our houses are kind of old and they’re not very tall. There are certain places that get shadows. In the past, that shadow would really impact the uniformity of the crop. Especially when we’re just beginning to propagate. Being able to have a toplighting makes the lighting way more uniform.

We also need supplemental lights for certain crops because of short days. We’re in Chicago, so there can be periods of time when we have very low light that goes on for a week on end.

GM: Are you planning to expand your supplemental lighting?

EL: We’re probably going to put more lights in some of our outside poly houses that we tend to grow cold crops in. We grow some early spring crops that are grown cold, but they like high light. This last year we did an anemone trial and anemones really like a lot of high light, so they did really well grown cold in these poly houses with the supplemental light. We did full LED and HPS light for those.

We’re also trying to transform some existing space that we used to cool bulbs. We don’t grow nearly as many bulbs as we once did, so we have a lot of cooler spaces essentially sitting empty. I’m working on a project to convert that vertical space into an LED-lit vertical operative type system.

Answers were edited for length and clarity.

Recent advances in LED technology have reignited an interest in plant lighting research because of four key advantages: reduced energy consumption, increased lamp life, options to manipulate the spectral output, and dimming capabilities. Most of these advantages are of special interest for assimilation lighting strategies that typically require high(er) light intensities.

Some LED lamps are capable of producing radiation outside the photosynthetically active radiation (PAR; with wavelengths between 400 and 700 nm) waveband, including ultraviolet (UV-B and UV-A; 280-314 and 315-399 nm, respectively) and far-red (FR; 700-800 nm) radiation. One nanometer (nm) equals a billionth of a meter. Note that visible light covers the 380-780 nm waveband and includes wavelengths associated with the colors of the rainbow (ROYGBIV).

Of late, research conducted using LEDs that combine PAR with UV and/or FR radiation has revealed new insights into plant growth and development and, in some cases, has opened up new market opportunities for crops that are sold for their enhanced appearance (e.g., leaf color).

All about PAR

Plant scientists commonly divide the PAR waveband into three distinct ranges: blue (400-500 nm), green (500-600 nm), and red (600-700 nm). While convenient, this approach causes a couple challenges: the wavebands overlap (e.g., 500 nm is considered both blue and green light), and it ignores some color wavebands used to describe visible light (e.g., indigo, yellow and orange).

McCree (1972) reported that single plant leaves that were acclimated to relatively low light intensities exhibited the highest rate of photosynthesis when exposed to blue (with peak sensitivity at 430 nm) and red (with peak sensitivity at 610 nm) light.

While these findings do not necessarily apply to the sensitivity of whole plants grown under a variety of light conditions, McCree’s results have long been used as the standard description of a plant’s sensitivity to light. This explains why the 3-way (blue, green and red) division of PAR has worked well and why many LED lamps used for assimilation lighting are designed with some ratio of blue and red LEDs corresponding to the peak plant sensitivities (resulting in an output consisting of variations of the color magenta/purple).

Overcoming waveband overlap

To prevent the issue of waveband overlap, we used the following waveband intervals to define the various (color) ranges: UV = 280-399 nm (including both UV-B and UV-A), Blue = 400-499 nm, Green = 500-599 nm, Red = 600-699, Far-red = 700-800 nm. Using this approach, the PAR waveband (400-700) is slightly different from the combined B-G-R waveband in that the PAR waveband also includes the 700 nm wavelength.

While some scientists only report the peak wavelength when describing the specific light color(s) they used, we believe that this is insufficient to fully characterize the light output from lamps. Some LEDs emit specific colors over a relatively narrow waveband, while others that deliver a spectrum with peaks at the same wavelength can emit light over a much wider waveband. When evaluating color (waveband) ratios, it is important to know how wide each waveband is so as to avoid any overlap from impacting the calculations.

Therefore, we suggest that in addition to the identification of the peak wavelength, the so-called full width at half max or peak (FWHM) of each narrow-band LED type be determined and reported (Fig. 1). Using both the peak wavelength and the FWHM of the spectral peaks more accurately describes the light output and its potential impact on plant growth and development.

Occasionally, scientists report lamp output ratios by counting the number of LEDs that emit across a specific waveband. For example, based on such assessment, a lamp composed of 80 red LEDs and 20 blue LEDs would emit radiation with a R:B ratio of 4 (80/20). This determination is incorrect since it does not include an accounting of the number of red and blue photons emitted by such a lamp. Thus, we strongly encourage the use of a spectroradiometer for all light ratio calculations.

Study methods detailed

We mounted a variety of lamps including incandescent (INC), compact fluorescent (CFL), ceramic metal halide (CMH), high-pressure sodium (HPS; both mogul base and double ended), and several LED fixtures (with different color output and wattage) in a 3-by3 meter darkroom. All lamps were mounted 2 feet above the sensor head of a calibrated spectroradiometer.

The sensor head was placed directly below the center of each lamp and several spectral scans were collected after each lamp had stabilized (i.e., warmed up sufficiently). The scans were averaged and the data were used to determine the spectral output across the various wavebands of interest, as well as the ratios of various waveband combinations (Tables 1 and 2).

The results of the lamp scans were compared to an outdoor scan of sunlight that was collected at solar noon on a clear day that occurred within three days of the summer solstice (June 21) in New Brunswick, NJ, USA.

Take home results

Table 1 shows the total light output (photon flux) across the 280-800 nm waveband (expressed in the units µmol m-2 s-1) for each of the light sources evaluated and for sunlight. The 280-800 nm waveband is sometimes referred to as the biologically active radiation. The INC and CFL lamp were included for comparison only since their low output will make it unlikely that they will be used for assimilation lighting.

For each of the wavebands shown, the table includes the amount of radiation as a percentage of the total radiation across the 280-800 nm waveband. In addition to the efficacy (number of photons emitted per unit of electric power consumed) of the light sources evaluated, Table 2 shows several ratios of the light (photons) emitted in each of the wavebands: R:B, R:G, G:B, R:FR and UV:B.

Obviously, other ratios can be calculated and, most importantly, it should be clear that the outcome of the ratio calculations is dependent on how the various wavebands are defined (i.e., what specific interval each waveband covers). Using different ranges for the wavebands (e.g., using the ROYGBIV wavebands as is common for visible light) will result in different ratios, and may therefore result in different interpretations about how the various lamps compare. This issue highlights the importance of standardization of the waveband ranges so that all researchers interpret their data based on widely accepted definitions.

As Table 2 clearly shows, the calculated ratios for each of the lamps varies substantially. Using sunlight as the benchmark, HPS lamps (and one of the LED lamps) have substantially higher R:B ratios. Similarly, the HPS lamps have much higher G:B ratios compared to sunlight. Not surprisingly, the magenta-colored output of two of the LED lamps has a much higher R:G ratio because their spectrum contains almost no green. Except for the INC lamp, the R:FR ratio for all other lamps is generally (much) higher compared to sunlight. While it is not clear at what point a much-increased R:FR ratio starts to substantially impact typical plant growth and development, these higher ratios resulted from the (very) small amount of FR light produced by most of the lamps.

The recent increased interest in the impact of UV radiation on plant growth and development prompted us to include data on the UV:B ratio. The data show that these ratios can be substantially smaller compared to sunlight. Especially the large amount of UV-A radiation in sunlight contributed to a higher UV:B ratio for sunlight compared to the lamps. Crops that can benefit from (some) UV radiation may need to be radiated with lamps that produce more UV radiation than the ones we tested. Obviously, working with UV radiation can be hazardous to biological tissue, so proper precautions are needed for both humans and plants exposed to such conditions.

While published literature on LED lighting applications is expanding, few reports include accurate information about light ratios across the biologically active radiation spectrum. And when ratios are described, they typically are the R:FR and the R:B ratios. Our results indicate that there can be substantial differences among the calculated ratios for sunlight and electric lamps, and not only for the R:FR and R:B ratios.

Of all the wavebands important to plants, outside the PAR waveband, the FR waveband has probably been studied the most. FR radiation has been reported to increase the rate of photosynthesis in some plant species. The most common peak wavelength associated with this effect is around 735 nm. Therefore, defining the 700-800 nm waveband as representing FR radiation, as was done here, includes perhaps too wide of a waveband. Researchers have suggested that it may be sufficient to use a narrower range centered around the peak wavelength. Ranges of 735 ± 25 nm, or even 735 ± 10 nm may adequately represent the impact of FR radiation on photosynthesis. Obviously, using narrower ranges compared to the 700-800 nm waveband we used will result in different ratio values depending on the specific spectral output of the light source.

While rather coarse, the division of the PAR waveband into blue (400-499 nm), green (500-599 nm), and red (600-699 nm) seems to work for plant lighting applications. However, this division seems arbitrary from the plant’s perspective and may need to be refined if, and when, research shows that more narrowly defined wavebands have specific and important impacts on plant growth and development. We encourage the scientific community to develop standardized definitions for important wavebands and adjust these definitions as warranted by new research findings.

Research has shown that LEDs designed to produce different colors can depreciate at different rates. That is, their output characteristics (intensity and spectral composition) change at different rates while the LEDs are operated for extended time periods. Therefore, the radiation ratios produced by lamps that contain such LEDs can also change over time. Users of LED lamps should be aware of this, and periodic testing should be performed to ensure that the desired radiation ratios are still provided by the lamps.

The bottom line

We strongly recommend using spectroradiometer data for all radiation ratio calculations.

We report substantial differences in radiation ratios among sunlight and a variety of common lamps used for plant lighting.

Standardization of the definitions of waveband ranges seems appropriate and desirable for plant growth applications.

Lamp efficacy values are but one of several performance characteristics that should be considered when deciding on the best lighting system for a particular application.

A.J. Both is a professor and extension specialist in controlled environment engineering in the Department of Environmental Sciences in the School of Environmental and Biological Sciences at Rutgers University–New Brunswick. Timothy Shelford is a part-time research specialist at Rutgers who also works at Cornell University. Claude Wallace is a Rutgers graduate and part-time employee.