Growing Soil

A couple of weeks ago, I overheard a conversation at Hayes Valley Farm containing the words “Lactobacillus” and “compost”. As I am a fan of both of these things, I felt it was my duty to butt in and see if I could provide any bacteria-themed facts. The result of this action lead Margaretha and I on something of a microbial scavenger hunt. The quest: to produce, well, a Lactobacillus compost.

If you have ever read a yogurt container or taken a pre or probiotic you have heard of Lactobacillus bacteria. These are the guys that eat lactose and poop out the lactic acid that gives yogurt its lovely sour taste. As a result, even if you are lactose intolerant, or can’t digest lactose high up in your digestive system, you can eat yogurt and not have the uncomfortable, lactose-induced side effects.

The “how” of producing the compost was really very easy (though a bit smelly). The recipe consists of a bit of old milk, some water that has been used to rinse white rice, and tap water. Friendly coffee shop people from down the street, who asked to remain anonymous, provided the milk and a good excuse to drink more coffee. A sushi restaurant close to the farm provided the rice wash. The water is courtesy of the city of San Francisco. The three ingredients were mixed together and left to sit to grow a lactobacillus-rich bacterial culture for about a week. The compost is ready to be sprayed on soil that could use amending as you read this. At the end of the article is the recipe for you to try on your plants at home.

“Why” (not to be confused with “whey”) one would want to make Lactobacillus compost remained a bit of mystery. Sour milk and rice? Lactobacillus? Why put it on soil. Was it even going on soil? The goal seemed to have something to do with creating an EM (or effective microorganism) culture. What do you do with a concoction of sour liquids and microorganisms after a week? The simple answer is soil building.

Soil improvement

The berms on Hayes Valley farm consist mostly of cardboard and wood mulch. In some places, the nascent soil has been amended with horse poop, compost, and chopped and dropped fava plants. None of it has been around for very long. What makes a soil good for plants is the same thing that makes any ecosystem a healthy and functional ecosystem: biodiversity.

Good soil is alive. It contains a huge variety of bacteria and fungi playing overlapping roles. Microorganisms living around plants in the phyllosphere (aka “the area around plants”) make nutrients like nitrogen, phosphorous and potassium available to plants. Without a microbially diverse soil, plants can’t get enough of the materials they need to thrive. Thus, you can add some NPK (or, nitrogen-phosphorus-potassium) fertilizer, which can be some fairly expensive and caustic stuff manufactured in large scale industrial processes. Or, you can gather some free microorganisms from the air or mature soil, give them stuff they like to eat (like sour milk and rice water) and introduce them to their new homes around plants that you want to make happy. You do not have to continuously apply the bacteria, but you do have to reapply NPK when the levels get to low. In fact, controlled studies have demonstrated that plants grown in the presence of Lactobacillus inoculum have lower production costs and higher net yields higher than those grown with conventional, chemical-based farming systems.


It is important to have a microbially diverse soil. Mature soil acts as an immune system for ecosystems. The more diverse the microbial populations are, the less likely single pathogens will be able to gain a stronghold and kill off plants. Luckily, it is pretty easy to encourage biological diversity in soil. The “founder” of soil science, M.W. Beijerinck stated, “Everything is everywhere” and his compatriot G. M. Baas Becking added, “but the environment selects.” This means, pretty much any bacteria can be encouraged to grow where every you want them, as long as you give them the right “environment” (food, temperature, etc.) to make them happy.

So, the microbial scavenger hunt is ongoing, and the Lactobacillus compost remains, for now, in big containers. This week we will be enriching the soil with the fancy new bacteria from this batch. In the future, we will be encouraging the growth of microorganisms obtained from mature soils from other areas around San Francisco. All of the microbial additions will hopefully lead to a microbially “mature” soil and, in turn, healthy plants.

Photos by Aimee Hill & Margaretha Haughwout, June 2010


Lactobaccilus Recipe

(Note: this method does not need to be followed exactly. You should be generally creating conditions which favor the bacteria you want to grow. The conditions should remain fairly warm and aerobic.)

  • “rice wash” (preferably 1 part rice, 2 parts water)
  • milk

Let the rice wash and milk sit in separate containers for about a week. Head space of about 50% or more should be left in each container and air should be allowed to get in. The resulting milk and rice should be somewhat sour. Mix 1 part aged rice wash to 10 parts milk. Add 20 parts water to this mixture. Make sure the container is only about 50% full and let sit for 5-8 days. Add to soil.

We shared our microbial adventure at last Tuesday night’s Kitchen Garden Workshop. For the latest updates and photos, please see: “The Lactobacillus Project with Aimee & Margaretha”