Dr Forest
EM-1 Effective Microorganisms
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Effective microorganisms (EM-1) — a live soil probiotic you activate and feed
This is a soil and compost biostimulant for plants. It is not a food, drink or human supplement, and is not tested to food-grade or supplement standards. Keep it for the garden.
Effective microorganisms (EM) are a live culture of lactic acid bacteria, yeasts and phototrophic bacteria, kept dormant in a mildly acidic liquid and woken with molasses and water. Add them to soil, compost or a kitchen caddy and you are topping up the working microbial life that drives decomposition, nutrient cycling and a healthy root zone. Dr Forest EM-1 is a 1-litre concentrate, brewed in small batches in Stockport.
One bottle is a concentrate, not a ready-to-use spray. Mix it with Dr Forest Unsulphured Molasses and water, ferment it for a week or so, and a single litre becomes 20 litres or more of activated culture. You control the freshness, you control the cost per litre, and there is nothing in it derived from animals.
What gardeners use it for
- Soil drench — water diluted culture into beds, borders and pots to build soil biology over a season.
- Compost accelerator — speeds the breakdown of a heap and keeps it sweeter-smelling.
- Bokashi fermentation — the microbial engine behind kitchen food-waste fermenting (pairs with bokashi bran).
- Compost-tea and microbial brews — a live starter culture for a living-soil routine.
- Seed & seedling soak — a weak solution before sowing or potting on.
- Foliar mist — well diluted, over leaves as part of a microbial programme.
- Animal housing & coops — a dilute spray to manage odour in runs, sheds and bedding.
- Wormeries & drains — supports breakdown and keeps things from turning foul.
Concentrate you activate vs ready-to-use sprays
Dr Forest EM-1 concentrate
- One litre activates to 20 litres or more with molasses and water.
- You brew it fresh, so the microbes are live when they reach the soil.
- Far lower cost per applied litre than pre-diluted products.
- Non-GMO cultures, no animal by-products.
Pre-diluted microbial sprays
- Already watered down, so you pay to ship mostly water.
- Shorter useful life once the culture has been sitting on a shelf.
- No control over the activation or freshness.
From Dr Forest — a grower-run brand based in Stockport.
What effective microorganisms are, and what the evidence actually shows
A consortium, not a single bug
The effective microorganisms approach was developed by Professor Teruo Higa at the University of the Ryukyus, Okinawa, in the 1980s. The idea is simple: rather than one isolated strain, you culture a stable community of compatible microbes that get along in the same acidic, low-oxygen liquid. The three groups in EM-1 are lactic acid bacteria, yeasts and phototrophic (photosynthetic) bacteria.
They sit dormant until molasses gives them a sugar source and water rouses them. Once active, they ferment rather than rot, which is why an EM-treated heap or caddy smells sweet and sour instead of putrid.
The honest evidence picture
The literature on EM is genuinely mixed, and it is worth being straight about that. A review of vegetable trials found a positive effect on growth in roughly 70% of published studies, with no significant effect in the rest (Olle & Williams, 2013). Long-term field work in China recorded higher wheat yields and better nutrition where EM was applied alongside compost over many seasons (Hu & Qi, 2013). Against that, a careful four-year temperate field study found no reliable effect on yield or soil quality, and concluded that much of any benefit tends to come from the organic matter EM is carried in rather than the microbes alone (Mayer et al., 2010).
The practical reading: EM is most dependable as a fermentation and composting aid, and as part of a soil programme built around organic matter — not as a stand-alone yield booster. Treat it as one input in a living-soil approach, not a silver bullet.
How the microbes earn their place
Lactic acid bacteria
Ferment sugars into lactic acid, dropping the pH. That acidic, fermentative environment is what keeps spoilage and putrefaction in check in a compost heap or bokashi bin, and is the basis of the same lactic fermentation used in silage and food preservation.
Yeasts
Produce enzymes, organic acids and growth substrates as they work through sugars. These by-products feed the other microbes in the culture and contribute to the breakdown of organic matter.
Phototrophic bacteria
Use organic compounds and root exudates and release amino acids and other simple compounds. Reviews describe these substrates supporting other beneficial soil organisms, including mycorrhizal associations in the root zone (Olle & Williams, 2013).
Fermentation over putrefaction
By steering organic matter down an anaerobic fermentation route, EM reduces the odorous compounds produced when material simply rots. This is why it is widely used in bokashi composting and for odour in animal housing.
Best alongside organic matter
Trials consistently show EM performing better with compost, manure or molasses than on its own — controlled work in beans found EM maintained leaf photosynthetic efficiency and lifted seed yield when applied to organically amended substrates (Iriti et al., 2019). Feed the soil and the microbes together.
Scientific references
- Higa, T. & Parr, J.F. (1994). Beneficial and Effective Microorganisms for a Sustainable Agriculture and Environment. International Nature Farming Research Center, Atami, Japan.
- Olle, M. & Williams, I.H. (2013). Effective microorganisms and their influence on vegetable production – a review. Journal of Horticultural Science & Biotechnology, 88(4), 380–386.
- Hu, C. & Qi, Y. (2013). Long-term effective microorganisms application promote growth and increase yields and nutrition of wheat in China. European Journal of Agronomy, 46, 63–67.
- Iriti, M., Scarafoni, A., Pierce, S., Castorina, G. & Vitalini, S. (2019). Soil application of effective microorganisms (EM) maintains leaf photosynthetic efficiency, increases seed yield and quality traits of bean (Phaseolus vulgaris L.) plants. International Journal of Molecular Sciences, 20(9), 2327.
- Mayer, J., Scheid, S., Widmer, F., Fließbach, A. & Oberholzer, H.-R. (2010). How effective are 'Effective microorganisms (EM)'? Results from a field study in temperate climate. Applied Soil Ecology, 46(2), 230–239.
How to activate and apply EM-1
Chlorine in mains tap water kills the cultures. Use rainwater, or stand tap water uncovered for 24 hours so the chlorine gasses off, before activating or diluting.
Step 1 — activate it with molasses
EM-1 is a concentrate. To get the most from it, brew a batch of activated culture first. The molasses is the food source that wakes and multiplies the microbes.
Activation needs Dr Forest Unsulphured Molasses. Use unsulphured only — the sulphur dioxide in sulphured molasses inhibits the microbes. (See your basket cross-sells, or search "Dr Forest Unsulphured Molasses" in our shop.)
- Mix. Combine in the ratio 1 part EM-1 : 1 part molasses : 20 parts warm dechlorinated water (for example 50 ml EM-1 + 50 ml molasses + 1 litre water). Stir the molasses until fully dissolved.
- Seal. Pour into a clean airtight container, filled near the top to limit air. Keep it warm, ideally 20–35°C.
- Burp. For the first few days, briefly release the gas that builds up, then reseal.
- Wait. Ferment for 7–10 days. It is ready when it smells sweet and sour and the pH has dropped below about 3.5.
- Use. Use your activated culture within about 30 days. Refrigeration extends it. A white film on top is normal; black, blue or foul-smelling growth means the batch has spoiled — start again.
Application rates
The dilutions below follow the product's standard guidance. EM is forgiving — err toward weaker rather than stronger, and apply little and often.
Soil & seedbeds
Water or spray a 1% solution onto the soil 2–3 weeks ahead of sowing, repeat just before planting out, and continue roughly every two weeks. Suits beds, borders, vegetables, soft fruit and ornamentals.
General garden & foliar
Apply as a soil drench or a well-diluted leaf mist as part of a regular microbial routine. Best on a dull day or in the evening, not in strong sun.
Animal housing & coops
Spray a 2% solution in runs, sheds, stables and on bedding to help manage odour, and onto slurry or muck heaps.
Allotment & plot scale
At land scale, apply 1–10 litres of EM per hectare depending on the crop and the condition of the soil, diluted into your watering volume.
Five common mistakes
- Using chlorinated tap water. It kills the culture before it can do anything. Rainwater or stood water only.
- Sulphured molasses. The sulphur dioxide inhibits the microbes — unsulphured is essential.
- Applying neat, or far too strong. EM works diluted and regular, not concentrated and occasional.
- Mixing it with chemicals. Pesticides, fungicides and strong feeds can wipe out the live cultures (see FAQ).
- Brewing too cold. Below ~20°C the ferment stalls and risks spoiling. Keep it warm.
Dr Forest Unsulphured Molasses for activation; Dr Forest Bokashi Bran for fermenting kitchen food waste; and our Liquid Veg & Bloom Boosters, which are already EM-fermented feeds if you would rather skip the brewing. New to fermenting soil microbes? Read our guide, what effective microorganisms are and how to use them, on the Dr Forest journal.
Keep the concentrate sealed, cool and out of direct sunlight; it stays viable for around a year. Do not freeze. Use activated batches within about 30 days, sooner if kept warm.
Effective microorganisms — your questions answered
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