Fortunately and unfortunately there are so many ways to manage pathogens in a hydroponic nutrient solution. Having options is great but these options can be difficult to navigate for new growers. Hopefully this overview comparing three popular management styles makes it easier to understand the tradeoffs between each.

Pictured above: Rhizoctonia and other root rot pathogens can spread through a recirculating hydroponic nutrient solution infecting all susceptible crops. Sterilization methods can help reduce the spread of spores in the nutrient solution while microbial inoculants can help reduce the chance of infection in individual plants.

Nutrient Solution Disease Management

There are many more decisions to make after selecting a general management style. For biological or hybrid technique, what inoculant and where should it be applied? For sterilization or hybrid, what is the best sterilization method for the specific farm design and what constraints can inform that decision? 

For more information on the many options for managing pathogens in a recirculating nutrient solution I recommend reading “Disinfestation of recirculating nutrient solutions in greenhouse horticulture” by David Ehret, Beatrix Alsanius, Walter Wohanka, James Menzies and Raj Utkhede. For more information on the many other considerations when designing a hydroponic farm for leafy greens production I recommend reading “Roadmap to Growing Leafy Greens and Herbs” by Tyler Baras (that’s me!).

To continue the conversation, email us and schedule some time with either Chris Higgins or our newest grower consultant Tyler Baras (aka The Farmer Tyler.)

Voluntary USDA grade standards designate different levels of quality in agricultural products. The USDA has official standards used to grade a lot of different crops including leafy greens like Greenhouse Leaf Lettuce, Field Grown Leaf Lettuce, Kale, Beet Greens, Collard Greens, Dandelion Greens and Mustard Greens. The standards for butterhead lettuce currently fall under the same standards used for Iceberg lettuce. Although the U.S. Standards for Grades of Lettuce do acknowledge the significant differences between the two types of lettuce, they are still grouped under the same standards. And there is no mention of living lettuce in the U.S. Standards for Grades of Lettuce, while living lettuce is one of the primary crops grown by hydroponic leafy greens growers. If the hydroponic lettuce industry is to grow beyond the premium product niche and enter the ‘real world’ of lettuce production, it would be helpful if hydroponic growers decided upon grading standards appropriate for hydroponically grown lettuce.

When hydroponic lettuce growers try to compete against field growers they almost never win in the battle for price per pound. Field growers can sell heads of lettuce wholesale under $0.75. Large hydroponic lettuce growers (3+ acres) can get their price per head close to $0.90. Field lettuce is generally packed in a 24 count box that will weigh 50+ pounds. The heads are easily 1 to 2 pounds. Hydroponic lettuce is often packed in a 6 or 12 count box and the heads rarely weigh over 10 ounces (0.625 pounds).

While hydroponic crops have a lot of external benefits like water savings and food safety, those benefits are not shown when a hydroponic butterhead is graded with the U.S. Standards for Grades of Lettuce. To preserve the narrative around hydroponic lettuce, it may be necessary to have USDA grading standards specifically for hydroponic lettuce so the crop does not lose some of its value when it enters the larger lettuce market that puts it ‘head-to-head’ with field grown crops.

USDA grade standards are helpful in international trade. The U.S. has one of the biggest lettuce importers on the northern border… Canada! (See Stats). Currently most hydroponic lettuce growers sell to local markets or if they are one of the larger hydroponic lettuce growers they might sell to a grocery store chain or produce broker that distributes their product in multiple states. I have seen living butterhead lettuce from Canada in the U.S. but I’m not aware of any U.S. hydroponic leafy greens growers shipping internationally. I would think that the increased shelf-life of living lettuce would be an advantage in international trade since lettuce is highly perishable.

The Standards for Butterhead Lettuce Quality

What should a USDA Grade A butterhead lettuce look like? How big should it be?

I’ve seen a wide range of targets from growers across the US and internationally. The majority of US hydroponic butterhead growers target a head that is between 5 oz. and 8 oz. (with roots attached). Many aquaponic and indoor vertical farms sell heads closer to 5 ounces. Many of the larger hydroponic lettuce growers (1+ acre greenhouses) target heads between 6-8 ounces. I’ve seen some greenhouse lettuce growers target 10 ounce heads. In Europe, it is common to see butterhead lettuce over 1 pound. In Japan, it is common to see living lettuce sold at less than 5 ounces. The market standards for hydroponic butterhead lettuce minimum weight vary but generally the bottom line is the head should not bobble around when packaged in a clamshell. Most living lettuce labels do not even state a minimum weight, instead the label might have “1 Count” or “1 Head”. Beyond weight there’s the more qualitative traits like leaf texture, leaf color and head formation. Check out these unofficial visual aids provided by the USDA to help grade romaine and lettuce. What would a visual aid for hydroponic butterhead lettuce look like?

Here are some of my favorite butterhead lettuces I’ve grown over the years, which do you think looks most like a ‘standard’ butterhead?

This article is property of Urban Ag News and was written in cooperation with Tyler Baras.