EM in the vegetable garden: doses, calendar, and bokashi mulch for living soil

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Watering your vegetable garden with effective microorganisms and spreading bokashi mulch around your plants: more and more gardeners are embracing these practices. But you still need to know the right doses and the right timing, and what you can reasonably expect from them.

Here are the manufacturers' guidelines, cross-checked against independent trials, along with a simple method for judging for yourself.

What you can reasonably expect

Let's be honest: the trials give mixed results.

• A four-year trial in Switzerland compared live EM with the same EM sterilized. It found no effect attributable to the microorganisms themselves on either yields or soil life. The small effects observed came from the material applied with them (bran, molasses).
• A review of 39 publications concluded there was a slight positive effect on average, but it varied widely between crops and was sometimes zero or negative.
• In Germany, one trial measured about 8% more wheat in one year, with no significant effect on the other crops or on profitability.
• A recent experiment found no measurable effect, at the recommended dose, on the decomposition of crop residues.
• On the other hand, long-term trials in Asia report better yields with compost made with EM than with conventional compost.

Our view: EM support the organic matter you add to the soil, especially when it has been fermented, but they can't work miracles on poor, bare soil. Our guide What the science says about effective microorganisms covers these studies in detail.

Key takeaways

What feeds soil life is, first and foremost, organic matter: compost, mulch, cover crops, crop residues. Think of EM as a complement to these inputs, never as a substitute.

Watering the soil with EM: dilution and frequency

Dilution

For watering the soil, the basic dilution is 1:100: 1.3 fl oz of EM-A per gallon of water (10 ml per liter), or 3.4 fl oz (100 ml) in a 2.6-gallon (10-liter) watering can. This is the dose given by the manufacturer of EM-A Microferm activated solution, and it also applies to the EM-A you make yourself from EM-1 mother solution (see our guide Activating EM-1). Other instructions call for a weaker dilution (1:250 to 1:1,000) but more frequent watering. Over the year, the quantities work out about the same.

Quantity and frequency

The manufacturer of Microferm recommends 1 to 2 quarts (1–2 liters) of product per 1,076 sq ft (100 m²) per year, spread out from spring to fall. In practice, a 2.6-gallon (10-liter) watering can diluted at 1:100 covers about 320–540 sq ft (30–50 m²), and you go over the area again every 2 to 4 weeks during the season, or 5 to 6 times a year. Several small doses are better than one large one.

The right conditions

• On moist soil, preferably in overcast weather or in the evening. Avoid full sun.
• With unchlorinated water: rainwater, or tap water left to stand for 24 hours.
• At the base of plants, using the watering can's rose, on the soil and the mulch.
• Never mixed with a fungicide, Bordeaux mixture, or any other copper-based product: these destroy the microorganisms. Leave at least a few days between such a treatment and an EM application. One manufacturer's instructions specify a minimum of 4 days.

Emy's tip

In dry weather, water first with plain water, then go over the area with your EM watering can an hour later. The microorganisms settle in far better in soil that is already moist.

The year-round calendar in the vegetable garden

• Late winter (February–March): as soon as the soil has dried out a little, prepare your beds. Add your compost (our guideline doses are in the guide Using your compost in the garden), spread the bokashi mulch, then give a first watering with EM. Allow two to three weeks before sowing.
• Spring (April–May): sowing, transplanting, and planting. The specific doses for young plants are in the guide Seeds, seedlings, and potting up with EM. Water the soil with EM every 2 to 4 weeks.
• Summer: keep the soil covered. Water with EM in the evening, never on parched soil.
• Fall (September–October): after harvest, leave the crop residues on the surface or sow a cover crop, spray diluted EM over the residues and bare soil, then cover with fallen leaves. This is also a good time to spread bokashi mulch on beds that are resting.
• Winter: nothing on frozen ground.

EM bokashi mulch

What is it?

Our EM Bokashi mulch for soil is a coarse organic material made from straw meal and apple pulp fermented with EM. Don't confuse it with kitchen bokashi, which is a highly acidic pre-compost of food scraps that must be buried 8–12 in (20–30 cm) deep and mixed into the soil (see our guide Burying your bokashi in the garden). The mulch, by contrast, is spread on the surface.

Doses

• Maintaining beds, flower beds, and the base of shrubs: 0.1–0.2 lb per sq ft (0.5–1 kg per m²) per year, according to the manufacturer. A 55 lb (25 kg) bag therefore covers 270–540 sq ft (25–50 m²).
• Planting: about 4% of the volume of soil in the planting hole, or roughly 1 quart (1 liter) of mulch per 6.6-gallon (25-liter) bucket of soil, well mixed.

How to apply it

1. Weed and moisten the soil.
2. Spread the mulch in an even layer, then lightly rake it into the top inch or so of soil.
3. Water, ideally with EM diluted at 1:100.
4. If possible, cover with your usual mulch (straw, leaves, dry grass clippings): it keeps everything moist and alive.

Precautions

• When freshly fermented, this mulch is slightly acidic at first. Keep it away from direct-sown seeds and very young plants.
• On a bed meant for fine seeds (carrots, radishes, lettuce), spread it at least two weeks before sowing.
• Its coarse texture is not suitable for seed-starting mix.

The bokashi juice from your kitchen bucket can also be used to water the vegetable garden, diluted at least 1:100 and applied at the base of plants. Our guide Bokashi juice: dilution, uses, and limits tells you everything.

EM, compost, and other inputs: what does what?

EM don't feed plants: they support the breakdown of organic matter. In fact, the clearest effects appear when they accompany compost or fermented material, and almost never when they are applied on their own to poor soil.

A few good combinations: water with EM right after spreading compost or mulch, spray it on a cover crop when you cut it down, or add it to the compost pile, which we explain in the guide Speeding up your compost with EM. The rock dusts and clays offered by some manufacturers follow a different logic, that of correcting the soil: have your soil tested first.

Orchards, berries, and large areas

• Fruit trees and berries: the same 1:100 dilution applies, under the whole canopy, in spring and after harvest. Bokashi mulch is spread at the same rate as on beds.
• Large areas: manufacturers allow a few gallons per acre (a few dozen liters per hectare) per year, in 4 to 6 applications. Follow the label and the supplier's advice. On a garden hose, a dosing spray nozzle such as our Aquamix, set to 1%, saves you trips back and forth with the watering can.
• Grapevines: some winegrowers are trying it, but we have only found anecdotal reports, with no published results.

Did you know?

To find out whether the effect comes from the microorganisms or from the molasses and bran that come with them, researchers compared live EM in the field with the same EM heat-sterilized. The result: most of the effect came from the material applied, not from the microbes.

Running your own trial with a control bed

The best way to find out whether EM make a difference for you is to compare, in your own garden:

1. Choose two neighboring beds of the same size, with the same soil and the same sun exposure.
2. Grow the same variety in both, sown on the same day, with the same compost and the same mulch.
3. Water one with diluted EM and the other with the same amount of plain water, on the same dates.
4. Record everything in a notebook: dates, germination, vigor, harvest weight.
5. Repeat the following year, switching the beds: a single season isn't enough to draw conclusions.

If you see no difference, you will still have learned something useful about your garden.

In summary

In the vegetable garden, EM are used diluted at 1:100, on moist soil, in overcast weather or in the evening, every 2 to 4 weeks from spring to fall, which comes to about 1 to 2 quarts (1–2 liters) of product per 1,076 sq ft (100 m²) per year. EM bokashi mulch is spread at 0.1–0.2 lb per sq ft (0.5–1 kg per m²) per year, or at about 4% of the soil volume in planting holes, away from seeds and very young plants. Trials show variable effects, often due to the organic matter rather than the microorganisms: always combine EM with compost and mulch, and judge the results with a control bed.

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Other topics in the guide

Vermicomposting30 fact sheets →Composting25 fact sheets →Bokashi24 fact sheets →