Don’t Use Compost Tea on Seedlings


THE MOST COMMON REASON WHY GARDENERS FAIL with raising seedlings indoors is the dreaded dampening-off. It strikes cruelly in the early stages of plant life causing the stems to shrivel and the young seedling to topple over and die. One morning you wake up and your plants are no longer vertical.

I’ve been told that the cause is a microbial imbalance that allows a plant pathogen, frequently Pythium ultimum, to infect the plant.

After pondering this for a while, a thought occurred to me. What if I could use compost tea to maintain microbial balance? Would this reduce the chance of dampening-off with my seedlings. Typically, gardeners use compost tea to increase the number of good microbes and create a balance between good and evil. So then, why wouldn’t compost tea work to improve overall seedling health and provide protection from pathogens?

Grass is always greener under the compost tumbler

My interest in compost tea first started when I noticed that the grass under my compost tumbler grew lush and green. The rainwater washed through the compost and created a solution that is the ultimate plant elixir.

My wife heard me marvel at my unintended success with growing grass under the compost tumbler and bought me the necessary equipment for a homemade compost tea brewer for my birthday. She got me a small aquarium air pump, cheese cloth and some molasses to go with my 5-gallon bucket and homemade compost. Now there’s a sexy birthday gift!

Brewing tea

Compost tea recipes are very easy to follow. Compost tea is typically made by mixing mature compost with water and incubating for about 24 hours. Air (pumped into the liquid so the little bugs can breathe) and other ingredients are added so that the good microbes exponentially multiply.

Here is a video from organic gardener Howard Garret that shows how it’s done:

A while back I used my new birthday gift to brew up a couple batches of tea and applied it to my plants in the garden, but the funny thing was that I didn’t see much if any improvement. I used it for both foliar feeding and as a soil drench, as the experts recommended. I chalked up the lack of success to the original compost not being “hot” enough with microbial activity.

Although it didn’t much help with my mature plants, it might still help with my seedlings. Right?

Compost tea on seedlings

It turns out that a 2004 study conducted by researchers from Oregon State University and the USDA Agriculture Research Service looked specifically at using compost tea on seedlings. The question they looked at was: Can you use tea to ward off dampening-off.

The researchers conducted the study on cucumber seedlings that had been intentionally infected with Pythium ultimum. They tested a number of types of compost made from a variety of original materials as well as a number of tea additives. Their testing methods used some of the best equipment possible to see if any of the teas would consistently suppress dampening-off.

The study showed that only compost tea made with the additives of kelp and humic acid were shown to consistently reduce dampening-off. None of the other formulations worked consistently.

The more startling conclusion was that tea made with molasses “inconsistently suppressed damping-off.” This probably had to do with the residual molasses that was in the tea, which could have actually feed the pathogens. Another important conclusion from the study was that diluting the compost tea, often recommended for seedlings, reduced any positive impact from any of the formulations.

My conclusion

Although many backyard gardeners can brew compost tea as it is described in so many places on the Internet, few can recreate the exacting methods required for success with dampening-off and seedlings. With this in mind, I would use your compost tea on mature plants and not on seedlings and even with mature plants expect inconsistent results.

1. Do Tumbling Compost Bins Work?
2. Composting Compostable Packaging
3. Seven Eco-friendly Ideas for the Garden

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6 Responses to “Don’t Use Compost Tea on Seedlings”

  1. January 7, 2011 at 11:41 am #

    Thanks for the link! Looks like a great site and I am looking forward to reading your posts. Thank you.

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