Season extension via row covers and high tunnels as well as year-round controlled environment production in greenhouses, and indoor vertical farms has allowed culinary herbs to be available out of season, thus meeting demands of market goers and chefs alike. Even with indoor production, during the winter the majority of fresh culinary herbs sold in the U.S. are produced in other countries.

Culinary herbs can be produced from seed and increasingly from shoot-tip cuttings, the former of which can have slow or poor germination and may be difficult to produce. In addition, vegetative cuttings allow growers to produce true-to-type plants which are more desirable and reduce young plant production time.

Daily Light Integral (DLI) learnings

Previous MSU research has determined that maintaining a DLI of 8 to 12 mol·m–2·d–1 during herbaceous floriculture crop young plant production produces high-quality plugs and liners, and reduces production time by 2 to 3 weeks depending on the genera.

However, little research-based information is available on the DLI requirements for rooting culinary herbs from shoot-tip cuttings. Subsequently, many growers produce culinary herb young plant under a range of DLIs up to 20 mol·m–2·d–1.

Taking the limited production information into consideration, we wanted to establish environmental protocols for producing culinary herb liners. We wanted to determine the daily light integral (DLI) range that would lead to uniform, complete rooting and high-quality liners of five economically important culinary herbs. In this first article, of the five-part series, we will show you how the DLI can be used to reduce rooting time and produce high-quality culinary herb liners.

Experimental protocol

Shoot-tip cuttings of Greek oregano (Origanum vulgare), rosemary ‘Arp’ (Rosmarinus officinalis), sage ‘Extrakta’ (Salvia officinalis), spearmint ‘Spanish’ (Mentha spicata), and thyme ‘German Winter’ (Thymus vulgaris) were stuck into 72-cell (28-mL individual cell volume) trays filled with a 50:50 (volume to volume) ratio of soilless substrate and coarse perlite.

Trays were placed on a bench with a root-zone heating set point of 73 ºF (23 ºC) in a glass-glazed greenhouse with an air average daily temperature set point of 73 ºF (23 ºC) and a vapor pressure deficit of 0.3 kPa. A 56% aluminum shade cloth was used to reduce the DLI to ˜5 mol·m^–2·d^–1 for 5 days to induce callus. A 16-h photoperiod was created by natural daylight and supplemental lighting from high-pressure sodium (HPS) lamps which provided light from 6-8 AM and 5-10 PM and turned on from 8-5 PM when the photosynthetic photon flux density was below ˜440 µmol·m^–2·s^–1. Overhead mist containing reverse osmosis water with a water-soluble fertilizer that provided 60 ppm nitrogen misted cuttings as necessary.

After callusing, trays were dispersed among DLI treatments of ~3 to ~16 mol·m^–2·d^–1 that were created with the use of no shade or shade cloth ranging from 36 to 76%. After 2 or 3 weeks, cuttings were harvested and morphological data was quantified to determine liner quality.

The following four plant characteristics exhibited the most significant variances when DLI was either increased or decreased:

Results

As the DLI during rooting increased from ~3 to ~16 mol·m^–2·d^–1, the stem length of oregano and thyme decreased by 36%, and 27%, respectively (Fig. 1). Stem length of spearmint decreased by 12% as DLI increased from ~3 to ~12 mol·m–2·d–1, (Fig. 1 and 2) while DLI did not influence stem length of rosemary or sage (Fig. 2).

The stem caliper of thyme and sage increased by 49% and 23% as DLI increased from ~3 to ~11 and ~15 mol·m^–2·d^–1, respectively (Fig. 2). As the DLI increased to ~16 mol·m^–2·d^–1, stem caliper of sage and thyme decreased. The stem caliper of oregano, rosemary, and spearmint increased by 26%, 28%, and 30% as DLI increased from ~3 to ~16 mol·m–2·d–1 (Fig. 1 and 2).

As the DLI increased from ~3 to ~16 mol·m–2·d–1, the root dry mass of sage increased linearly by 421% (Fig. 2). Additionally, the root dry mass of spearmint and rosemary curvilinearly increased by 328% and 449%, respectively, as DLI increased from ~3 to ~16 mol·m^–2·d^–1 (Fig. 1 and 2). The root dry mass of oregano and thyme increased by 106% and 436% as DLI increased to ~12 and ~14 mol·m^–2·d^–1, respectively (Fig. 1 and 2). Further increases in DLI did not increase root dry mass for oregano and thyme (Fig. 1 and 2).

The shoot dry mass of oregano and spearmint linearly increased by 117% and 125%, as DLI increased from ~3 to ~16 mol·m^–2·d^–1(Fig. 1). At a DLI of ~14 mol·m–2·d–1, the shoot dry mass of rosemary increased up to 53% and at a DLI of ~13 mol·m^–2·d^–1, shoot dry mass of sage and thyme was 104% and 142% greater, compared to a DLI of ~3 mol·m^–2·d^–1(Fig. 2). As DLI increased to ~16 mol·m–2·d–1, the shoot dry mass of sage and thyme decreased by 8% and 5%. (Fig. 2).

Take-home message

High-quality liners of oregano, sage, spearmint, rosemary, and thyme were produced under DLIs between ~11 and ~16 mol·m^–2·d^–1, which is higher than propagation protocols for rooting floriculture crops.

Whereas, a DLI of ~11 to ~12 mol·m^–2·d^–1 was best for thyme. Spearmint liners produced under the highest DLI of ~16 mol·m^–2·d^–1 were of exceptional quality as they were compact, had higher root, shoot, and total dry masses, and a greater stem caliper.

However, necrotic lesions developed on leaves (Fig. 3) as a result of the high DLI. From the overall rooting results, desirable characteristics, and aesthetics of liners from this experiment, we suggest propagating fast-rooting herbs such as spearmint and oregano cuttings under a DLI of 11 to =15 mol·m^–2·d^–1 for 9 to 11 days after callusing. Slow-rooting culinary herbs such as rosemary and sage will require at least 3 weeks under a DLI of 11 to =15 mol·m^–2·d^–1 after callusing, and thyme cuttings should be propagated under a DLI of ~11 to ~12 mol·m^–2·d^–1 for at least three weeks after callusing for best liner quality. We would also like to note that higher DLIs (=12 mol·m–2·d–1) may result in leaf chlorosis and/or necrosis (Fig. 3) but this does not affect the final product once moved into a common growing environment and fertilized with higher nitrogen rates.

In August, San Francisco-based vertical farm Plenty announced that its products will be sold in 430 Albertson’s stores in the U.S. According to Plenty CEO Matt Barnard, the company’s deal with Albertson’s stemmed from Plenty’s ability to deliver product amid the pandemic. “Through all of that, we continued to deliver week-to-week and increasing our weekly shipments by three times and still delivering with around a 99% fulfillment rate,” he says. “That really highlighted the power of our farms.”

Produce Grower: How did the deal with Albertson’s come about?

Matt Barnard: We had been building our presence in retail. We first entered the grocery market back in 2018 and then in 2019, we set about building that presence. And Albertson’s execs came out for a farm visit and a taste earlier this year. During the farm tour, they were blown away and we started working to get us on their shelves quickly. We were on the shelves in some stores in a matter of weeks and it started flying off of their shelves in a category lead. And shortly after, COVID hit and the power, speed and resilience of our platform and our farm really shined through as there were extreme demand surges and food chain shocks.

PG: What does the opportunity for an in-person visit offer that a Zoom call cannot?

MB: It really does matter. When someone hears about our farm, it can be interesting [to them]. But when they show up at our farm, I think it’s breathtaking. And you see all of the growing, thriving lettuce. You can smell it. And once you taste the plants we’re growing, it’s unusual and uncommon and flavorful that people are taken [by the farm]. Any skepticism tends to melt away

PG: How are the details of the deal hashed out?

MB: It’s all about how far people want to go in each stage, as well as the constraints of their footprints and the service radius of our farms. Take Albertson’s, for example. They have their California footprint, and we have our farm where we prefer to keep our service radius as low as we can because we very much prefer a local and even hyperlocal model. So when you toss that all into a tumbler and it all shakes out, we’re targeting over 400 locations in California to start off with. They have a national footprint beyond that, but our first step is our Compton farm and serving California from there. ... The Los Angeles market is extremely important because of the way the Los Angeles community generally has shown that leafy greens are a big part of their diet.

This year has certainly been a year like no other. For more than five years, Produce Grower magazine has surveyed the industry by reaching out to growers across North America to see how their operations are faring and we're seeing some new developments. This year, we analyze the impacts of COVID-19 on the market, especially when it comes to e-commerce and staffing issues.

There’s good news in there, too. Direct-to-consumer sales of finished produce hit a five-year high in 2020, and sales of both edible transplant crops and finished produce at independent garden centers rose.

Crop diversity seems to be increasing, with tomatoes and lettuce taking the top two spots, but by a much smaller margin than we’ve witnessed in previous years. Herb production continues to increase, moving into the third spot for the first time this year.

The data seems to indicate that growers are branching out into new territory with many varieties seeing higher numbers like hot peppers, melons, pumpkins, zucchini and spinach.

Read on for more insights into the rapidly changing CEA market. – Kate Spirgen

As traditional outlets for CEA produce struggle in the midst of the coronavirus outbreak in the U.S., growers are looking at new ways to deliver their fruits and vegetables to consumers. In this year’s State of the Industry report, we found a myriad of changes not only in the way growers are selling, but in what they’re selling as well.

While some are seeing great opportunities in the increasing demand for local produce, others are struggling to find workers and fill the gaps left by their once-steady restaurant customers, who are on the front line of COVID-19’s impacts.

Berry production is on the rise and growers are diversifying their crops more than we’ve seen in the past five years. While lettuce, tomatoes and cucumbers still top the charts, they no longer dominate the way they have in years past. Herbs are having their day in the sun, taking over as the third most popular edible crop.

Some of this change in demand, such as more people cooking at home, can be attributed to the coronavirus, but other shifts, like an increasing market for berries, is a trend we’ve seen coming before the pandemic.

The future may be cloudy right now, but one thing is for sure: Consumers are buying online. A full 15% of growers started selling online for the first time this year and direct-to-consumer sales are soaring. It’s a trend floriculture greenhouses and independent garden centers are seeing as well. The ease and simplicity of shopping online are huge draws and will continue to attract customers once the COVID pandemic is under control.

The good news is that it’s not too late to hop on the direct-to-consumer trend. While the coronavirus is pushing it to the forefront, it’s an outlet that consumers have wanted, and it looks like they’ll continue to buy straight from the grower in the coming years. Whether it’s CEA sign-ups, direct-to-door deliveries, subscription programs or the traditional farmers market, today’s consumers prefer to go directly to the source for products they can trust.

Building that trust and creating a lasting connection is something CEA growers can work on now, and for years to come no matter when the pandemic ends.