Investigating iceberg lettuce in the hydroponic greenhouse – 2013 Trial, Part 1

Why isn’t there hydroponic greenhouse iceberg lettuce?

Lettuce is the 2nd most popular vegetable in the US (second only to potato), and head lettuce is certainly the most recognizable type. So, it is not uncommon for us to hear the question “Why don’t you produce iceberg lettuce in the greenhouse?” There are, in fact, several key reasons iceberg lettuce is not commonly grown in vegetable greenhouses in the United States. They are listed below and loosely ranked by importance, but these reasons may vary depending on production area and market.

1) Market potential and price

One of the most important reasons that we do not see head lettuce in the greenhouse is because the economics of the market are not always encouraging. Nearly all of US head lettuce is produced in California (spring through fall) and Arizona (winter). Huge expanses of open field production are dedicated to lettuce production in some of the most productive cropping areas in the world. Soil and climate factors make these regions quite appropriate for head lettuce production and the scale of production also contributes to competitive advantages. For example, recent terminal market data reported that head lettuce cartons (approximately two dozen 2 lb. heads of lettuce) are selling for $11.00 to $17.00. These prices illustrate that greenhouse producers are unlikely and unwilling to produce head lettuce at prices that could be competitive with field production. An additional facet to this topic of markets is that recent per capita consumption of head lettuce has been flat or on the slight decline as other leafy vegetables have become more popular.

Iceberg lettuce typical in California open field production. Specific cultivars are slotted in specific times of year for production regions of CA and AZ across the entire year.


2) Production time

Typically in the open field, head lettuce matures in 70 to 80 days in the summer and up to 130 days in winter or lower light and temperature seasons. Of course one of the benefits of greenhouse production is the potential for faster growth rates and reduced production times. To date, in summer greenhouse production in OH, we have harvested our iceberg lettuce approximately 55 to 60 days after seeding. However, the total weight of our lettuce may not equal field packed cartons. This production time contrasts with a bibb production schedule in the greenhouse which might produce a crop in 40 to 50 days.

3) Nutrition

As consumers become conscious of the nutrient and antioxidant levels in their food, they continue to become more discerning in food purchases. Due to underlying genetics, plant growth form and a few other factors, iceberg lettuce is not the most nutrient dense leafy green vegetable. The table below (From USDA National Nutrient Database for Standard Reference Release 24 ) gives average nutrient information for the most common types of lettuce. Remember that these are averages from primarily soil grown crops from around the country, so they do not represent the exact profile of product from individual greenhouses or cultivars. Nevertheless, this table does support the generally held perception that iceberg lettuce contains fewer nutrients per serving that other lettuces and certainly other leafy greens. However, keep in mind that iceberg lettuce from greenhouses has been less often evaluated than that from the open field.

4) Customer Preference and Perception

This potential reason for the lack of iceberg lettuce in US greenhouses is linked with the nutrition topic discussed above. Most greenhouse lettuce producers are growing and marketing their crop as a premium product. This means that the quality of the crop is crucial, but the perception of the crop is also important. Iceberg lettuce is often viewed by many discerning consumers as inferior in taste, visual appeal, and nutrition to the bibb, romaine and leaf lettuces. There is also little attraction based on novelty or distinctiveness. These views mean that many of the most profitable potential customers for hydroponic greenhouse producers may be less interested in iceberg than other leafy crops. However, if greenhouse producers were able to market a product with comparable attributes (crisp, multiple servings per head, etc) and improved taste, freshness, or nutrition, these perceptions and preferences could change.

5) Adaptability of cultivars and environments

Much of greenhouse lettuce production (especially bibb) utilizes cultivars that were specifically bred and developed for greenhouse environments. These cultivars can generally be depended upon to perform consistently across seasons and even geographic areas. When investigating types of lettuce, like iceberg, that are less often produced in greenhouses, preferable cultivars and knowledge of how they may perform is limited.

Additionally, iceberg lettuce often requires specific environmental conditions to produce the tight head consumers are accustomed to- without bolting or becoming bitter. So, even though we can control temperatures closely in greenhouses, producers may not be able to exactly emulate conditions that are common in field iceberg production. There may be more seasonal constraints of light and temperature on iceberg production in many US greenhouses than we experience in producing other types of lettuce.

So, why would we be interested?

After spending the time to try and elucidate why iceberg is rarely produced in hydroponic greenhouses, you are probably asking what would possibly be the attraction. While I will be the first to admit that greenhouse iceberg is unlikely to become a US market force in the near future, there are some reasons for investigation.

First, familiarity is not always a negative. Some consumers will always be attracted to what they know best and producers should always be ready to fill small market niches if they are possible and profitable- especially if they can provide a product with superior quality.

Secondly, we at CropKing deal with producers not only in the US, but also internationally. Market demands and dynamics may differ considerably in these areas. For instance, in the Caribbean islands where imports are expensive and often of poor quality, iceberg may be both desired by consumers and potentially profitable for greenhouse growers.

Thirdly, it is always important to investigate potential crops and understand both the benefits and drawbacks to their cultivation to assist current and future producers- essentially, we need to have solid backing to the answers that we give growers.

Goals and Early Observations

Main Objectives

  • Produce 5 iceberg cultivars in spring and summer greenhouse environments in OH
  • Evaluate yield as well as broad metrics of internal and external quality
  • Evaluate production timing and suitability for the CropKing NFT system

After one run, we observed

  • Head lettuce production was possible
  • Head weight and density may not be the same as field iceberg
  • Not all cultivars appeared to be well suited to our conditions because some bolting and tipburn occurred
  • Anecdotally, the taste of the produce was encouraging
Lettuce research Greenhouse greenhouses hydroponics