Is Your Organic “Compost Tea” Causing a Problem?

A recent article in American Fruit Grower written by Dr. Trevor Suslow – UC Davis, has been showing up in many publications and it certainly caught my eye. As we think about summer; market gardens and farms; vegetable and fruit harvests; farmers markets and roadside stands; we have to consider what might happen with our harvests once they leave the farm. Organic producers are part of the solution to healthy food but not if we are lax in how we treat and handle the food we sell!

Organic vegetable producers face an uphill battle trying to produce a fast growing vegetable crop that demands high soil fertility, especially nitrogen, and most of our natural organic sources are low in nitrogen and that nitrogen is only slowly available. If you have been growing organically for several years you may have built up your soil N reserves through good crop rotations, use of legumes and compost but there are times when we need a biofertilizer and/or a biostimulant. Especially as you near harvest when plant requirements are at their peak it is only natural to see a plant show physical signs of nutrient stress and you know you need to do something!

Fortunately, we do have some tools in organic agriculture that are approved for use in these periods but (back to that article) Dr. Suslow’s interesting article discusses the downside to applying these tools that may surprise you. On farm experimentation with the making of “compost teas” may be the closest example of a potential problem on the small to mid-sized organic vegetable farm. There is a right way and wrong way to make compost tea. In his article he talks about this formulation being a great source of nutrients for bad bacteria and fungi. Foodborne pathogens like salmonella can be introduced into these formulations very easily and then they use the nutrients in the mix to grow to very high populations. When a grower then sprays this “compost tea” on their crop there is a real danger that these pathogens are on the produce.

How do the bad bugs get into “compost teas?” Most of the organic producers I know love to harvest rainwater and then use that rainwater in a variety of ways. One of those ways is making compost tea. Certainly the rainwater has some nitrogen in it from the rainwater and it is usually a lower pH, another benefit to microbes. But, this rainwater off a roof, can have Salmonella, E. coli and Listeria from birds or other wildlife on the roof. In general they won’t grow too much without a food source but adding your compost may be that food source.

Let me stop here and give you a link to the article. His explanation is much better than mine! https://www.growingproduce.com/farm-management/a-wake-up-call-for-growers-on-biostimulants-and-biofertilizers/?e=bob.whitney@ag.tamu.edu&utm_source=omail&utm_medium=newsletter&utm_campaign=afgenews06162021

Author: Bob Whitney, Regents Fellow & Extension Organic Specialist

Agriculturalist, extension educator and researcher, organic agriculture enthusiast and promoter, international program developer, Christian, husband, father and friend.

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