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The soil in the garden is contaminated with viruses, fungi or bacteria, the compost needs to be germ-free or potting soil is needed for new plants. Here it is helpful to heat the compost soil used accordingly and to kill anything harmful that is in it. Buying an earth damper is not cheap and often not necessary if only a small amount of material is to be dampened. But there are other types and one or the other self-made earth damper if it does not have to be used all the time.

Steam compost, why?

As a fertilizer, compost soil is supposed to help the plants to grow well and produce a lot of yields. If it is mixed under the soil, it should therefore be germ-free so as not to infect the garden soil with bacteria, fungi, pests or viruses. Because when composting, all sorts of plant parts from the garden come together that could well be covered with fungal spores or bacteria. Pests, on the other hand, such as grubs, are spread by the beetles that lay their eggs here in the compost heap. If the fertilizer is then mixed under the garden soil in the beds, the plants can quickly be threatened with extinction. These pathogens can be killed by moist heat, heating the soil and compost to around 80 °C in conjunction with moisture in the form of steam is completely sufficient here. There are the following possibilities to build earth dampers or to use other devices for this, which are also not expensive at all:

  • Grill and aluminum pot
  • Use the microwave (for small quantities)
  • Use the oven (also small amounts)
  • Steel drum or drum with lid

notice: A commercially available earth damper, for example a steam wheelbarrow, consists of a wheelbarrow with a built-in electric steam generator, grid, thermometer, filter and lid. However, these devices are very expensive with a purchase price of 1,600.00 euros.

Grill and aluminum pot

If large amounts of compost are not to be steamed every day, purchasing a soil steamer from a specialist dealer is usually too expensive and not worth it. If you want to steam a little compost before mixing it in with the garden soil, then the conventional grill is suitable for this, regardless of whether it is electric, gas or charcoal, as well as a suitable pot. The instructions for self-construction are very simple and can also be quickly dismantled and stowed away afterwards. The following materials are required for the barbecue earth steamer:

  • grill
  • Gas bottle, socket or charcoal
  • Aluminum pot with lid
  • suitable steam insert
  • cloth
  • possibly a thermometer

For example, the large steam juicers, which already consist of four parts, are suitable for the aluminum pot. The water is poured into the bottom pot, the steam escapes via the collecting pot for the juice, the compost to be steamed is in the top pot and the lid is placed on top. The old preserving pots, which usually have a thermometer in the lid, are also suitable.

tip: It used to be common to use a pot for juicing. These old pots are often still in the grandparents' basement, and you could also find them here for little money at a flea market or an Internet second-hand goods site.

Instructions for building your own

If you want to build the earth damper yourself, you should follow these instructions for self-construction. If the above materials have been procured, then the earth damper can be assembled as follows:

  • Fill the lower part of the aluminum pot with water
  • Place a cloth on the steamer grid
  • this is followed by the compost
  • can be slightly moistened
  • put the lid loosely on the pot
  • Plug in the thermometer
  • put everything on the fired grill

If the pot has warmed up to 80° Celsius according to the plugged-in thermometer, it stays on the grill for about 30 minutes. However, if the temperature rises significantly, the lid should be aired in between. Because at higher temperatures, the nutrients in the compost soil can also be damaged.

tip: As an alternative to the grill, if you don't have one, you can also heat the pot on a stove and put it under steam.


The microwave is only suitable for very small portions, but it also serves its purpose well as an earth steamer. The steaming time can also be shorter with the microwave. When using the microwave for sterilization, you can proceed as follows:

  • use a microwaveable dish
  • do not use them later in the kitchen
  • Fill in desired small amount of compost
  • moisten them well
  • give up the lid
  • Steam on high for ten minutes
  • let it cool down well

tip: The advantage that also occurs when steaming the soil is that the trace elements and nutrients in the compost are released immediately and not only after a few weeks, so the plants benefit immediately.


The oven is also suitable for sterilizing small amounts of composted soil, for example if you only want to fill individual pots or a balcony box. To do this, proceed as follows:

  • fireproof bowl that is no longer needed in the kitchen
  • Fill about ten inches high
  • Lay aluminum foil loosely on top
  • alternatively poke a few holes
  • Steam must be able to reach the earth
  • Fill the drip tray with enough water
  • Set the oven to 80°C
  • Note the heating time
  • then leave in the oven for 30 minutes
  • Turn off the oven, open it and let it cool down

notice: If the smell bothers you, you can also use a roasting bag to fill with the soil. Then you have to moisten the composted soil well beforehand, otherwise there will be no germicidal steam in the well-sealed hose.

Steel drum or drum with lid

The advantage of the steel bin is its size, because a large amount of compost can be sterilized in it at once. In order to be able to use the steel barrel on a fireplace, you must take safety precautions:

  • find a safe place
  • no trees or shrubs in the immediate vicinity
  • put stones on the ground
  • build a small stone wall around it
  • in this fireplace the fire can burn safely
  • use a stable grid as a cover
  • the heavy barrel will stand on this later

tip: If the fireplace is securely set up, it can be used at any time for steaming the compost, but also for other purposes. So you can build seats around the spot and sit comfortably around the campfire in the evening.

Steaming in steel barrel

If you want to steam the compost in the steel bin, you should always work in pairs. Because the barrel alone is already heavy and you have to put it on the grid on the fireplace. After that you can fill in the soil. The advantage here is the large amount that can be sterilized in a single operation. You must first moisten the filled soil with a hose. Then proceed as follows:

  • ignite a fire
  • Put the lid on the bin
  • Plug in the thermometer
  • If the temperature gets too high, remove the lid
  • so steam can be let off
  • leave for 30 minutes at a temperature of 80 °C
  • then put out the fire
  • let the earth cool down
  • then remove from bin and recycle

A preserving thermometer that is big enough to put in the top of the bin can also be used as a thermometer. Alternatively, you can drill a sufficiently large hole in the lid into which the thermometer can be inserted.

notice: So-called thermal composters are also commercially available. However, these are not recommended for soil decontamination. Because the steam required for this cannot form here due to the lack of ventilation slots and therefore the cutting waste decomposes faster with this composter, but bacteria, pests, viruses and fungi remain present.

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