The suggested application rates for EM to soil and plants in our gardens vary widely. The 2 main manufacturers in North America suggest a rate of 1 gallon per 1000 sq ft per year, split into regular applications such as monthly, at a dilution rate of 1:1000, or as low as 1:100 for certain uses such as lawns. This translates to perhaps 1/2 L per 1000 sq ft once a month for 8 months of the year, mixed with as much as 500 L of water. They say this is based on many years of experience and research.
This is the advice I have always given, but I proposed that a lower dilution rate such as 1:100 for foliar applications would be acceptable, simply because applying 500 L of water to the 1000 square feet is an awful lot of water. It may be feasible with a hose-end sprayer, but certainly not with a 15L backpack sprayer.
Also, I have always been confused as to why the suggestion application rate is generally 10-40 times less for agriculture. I decided to delve into the research and see how much EM they are using, how much they are diluting it, and what results they are getting. It proved rather difficult to find the exact data I was hoping for, but I did learn a few things. All of the research comes from agriculture. I even found a couple of trials by Ana Primavesi.
One research trial by Ana Primavesi looked at the importance of focusing on organic matter in the soil while using EM. She found that the amount of EM applied must correspond to the organic matter content of the soil. If too much EM is applied, it can lead to rapid OM breakdown and loss of soil structure, i.e. compaction. The EM use is often very beneficial for the first 2 or 3 years in a temperate climate such as ours, but problems can occasionally be seen after that. The study didn't come up with any data that was very useful to me in terms of how much organic matter to add (12 to 14kg of fresh OM or 3.5 to 4kg of dry OM for each ml of EM, but how much OM are we starting with?), but it was interesting to note that they were only using 10 ml per 1000 sq ft, at a dilution of 1:200.
Another Primavesi study tested to see how much EM should be applied to a soil with 3% organic matter. Our soils can easily be that low or lower. She found that lower amounts of EM are better on low OM soils. The best was again, 10 ml per 1000 sq ft, and it was done 4 times (so 40 ml). The dilution rate was not given.
On a vineyard in Yugoslovia, powdery mildew was largely controlled with EM at both a 1:200 ratio and a 1:5000 ratio. I can't quite figure out the appliation rate, but it seems that it was about 50 ml per 1000 sq ft and 2ml per 1000 sq ft, respectively. This was done 7 times throughout the growing season.
An organic farmer in Colorado uses EM for many purposes. He saw big yield increases in his peas when applying 85 ml per 1000 sq ft 7 times over the course of one month, diluted 1:400. He saved a lettuce crop from Botrytis with regular applications at a dilution of 1:333. He controlled alfalfa weevil with a dilution of 1:300. It is interesting to note that he sprayed both fields with liquid fish, liquid kelp, and molasses, but he also needed the EM for control of the weevil. His yields were also 50% higher in the EM-treated field.
Rice was sprayed with 110 ml per 1000 sq ft, 3 times, diluted 1:100, with favourable results.
Corn was sprayed weekly at a dilution of 1:1000. Both city waste and pig pens were sprayed 1:100. All had favourable results.
Frenchbeans were sprayed with dilutions of 1:100 and 1:500. Both performed well, but the most beneficial was at 1:500. More is not always better.
In Vinny Pinto's book on agricultural EM use, he suggests ratios of anywhere from 1:100 to 1:1000, but he says not to apply to tender leaves below 1:300. He generally suggests 85 ml per 1000 sq ft, at least 3 times a year and preferable more like once a month for the first couple of years.
These are just some of the many research trials that have been done over the past couple of decades. There truly is a lot of information out there on EM use in agriculture, but I'm not sure why the lower agricultural applications have not been applied to urban garden applications. Is it purely marketing and profit motives? Is it because these are more "high-value" landscapes? Or is more really better? It is certainly apparent that this is not an exact science.
The many researchers use widely varying application rates and dilutions in agriculture with much success. I believe we should begin experimenting with using less EM and higher dilutions (more water). It seems to me that 1/3 cup (85 ml) per thousand square feet would be a good place to start. This would make it easier to have higher dilutions. I think that 1:100 should perhaps be a minimum for foliar and crop applications. If you can't use that much water, try using less EM until you have that 1:100 ratio. If you can use more water, do so. Remember how 1:500 outperformed 1:100 in the one trial and how 10 ml per 1000 sq ft was better than higher amounts in the other?
Another trend is that regular applications are important, particularly in the first couple of years. This is not new information, but important to remember. In the research, the EM is often applied with an equal amount of blackstrap molasses to give the microbes some nutrients and carbohydrates, and to help the EM stick to the leaf surface.
Also, it is apparent that it is important to also increase the organic matter content of the soil while using EM. If the OM content is low, EM can cause some problems over time. Keep the leaves and grass clippings in the yard.
So, in summary:
- let's try some lower application rates, perhaps starting with 1/3 cup EM per 1000 sq ft
- it should be diluted at least 1:100
- it should be done regularly, perhaps once a month or more
- it is a good idea to apply it with an equal amount of blackstrap molasses, as well as biostimulants like sea minerals, liquid kelp, and liquid fish
- we also need to increase the organic matter content of the soil
I hope to find more studies on this, but it's actually a lot of work! If you find any good research on application rates and dilutions, send it my way.