Due to its composition and inherent organisms, soil has a fundamental impact on plant growth. For healthy development, seedlings depend on optimal growth conditions provided by soil. In particular intensely used horticultural soils have problems, since they amass many pathogenic organisms and substances.
Practical experiences of applying hot steam have shown that conservative methods of heating soil in general have a positive effect on plant growth. Hot steam has a physical, biological and chemical effect on intensely used soils and solves the majority of issues without chemicals.
Nevertheless until today not all effects of hot steam on each plant type is scientifically clarified in detail due to the complex dependencies between plant types and soil components.
In practice hot steam kills the majority of diseases and releases abundant nutrients, in particular nitrate, which is made available for plants in soluable form through condensation. After steaming plants are healthier: A culture shows more equality in growth and can be planted earlier in temperate zone, since soil is heated up and resting period is shorter in comparison to chemical usage. However there are exceptions where steamed soil can cause growth depressions e.g. with lettuce. The reason for which can not be clarified yet. It is assumed that in some soils the rate of nutrients has been negatively changed by heat. Normally soil born organisms compensate this effect. In steamed soil however it takes time until those organisms have resettled.
Hence it is recommended, in particular for sensitive cultures, to either wait two to four weeks before planting by extending the cooling period or – in order to cut down on the duration of the cooling period – to inject active beneficial micro organisms into the soil in order to facilitate and accelerate the recreation of soil equilibrium. Furthermore those beneficial organisms hinder pathogenic organisms to resettle in particular those coming from deeper soil layers which have not been steamed.
