The growing period during which the mycelium grows throughout the compost and the casing layer is known as the vegetative phase and must precede a feeding process. The vegetative growth refers to the colonization and enzymatic degradation of the substrate inhabited by a mushroom. The colonization occurs from the moment during which the mycelium contacts its surroundings, and ends when the colonized environment is fully overgrown. First, available environment structures i.e. compost and casing layer get covered by mushroom mycelium. This period is relatively short and usually takes about 3-5 days. The colonization rate depends mostly on the ratio of mycelium volume to the volume of the occupied environment, as well as the availability of usable carbohydrates, moisture, structure and temperature.  During colonization a gray mycelium develops covering substrate or casing layer and subsequently changing microflora within feeding environment.  The changes happen in two independent courses of action, the biosupression that is an elimination of unwanted microorganism, particularly antagonistic microorganism and the commensalism, which is a process favoring development of useful microorganisms, mainly Scytalidium thermophilum – in the substrate, and Pseudomonas putida – in casing. The entire process is dependent upon carbon dioxide content and the amount of hydrogen peroxide production. A feeding process begins when enzymes become active.  At the beginning of the process obtained nutrient ingredients are used to continue mycelium growth in order to control environment. Subsequently, nutrient ingredients that are obtained from enzymatic degradation and their transport to fruiting bodies cumulate in rhizomorphic mycelium (white, thick strings). This phase is considered complete with a transition into generative phase, and forming fruiting bodies stage begins.

The producers address the important question in regards to the duration of the time required for compost colonization that would provide the highest yields at well-balanced feeding conditions.

To achieve the best results the following conditions should be provided.

1. The colonization period should be short. Only fully colonized compost can be an effective source of substrate nutrients in enzymatic feeding. The duration of compost colonization by mycelium is a very important feature, which allows evaluation its selectivity. Quick colonization protects the compost against the development of unwanted, competitive organisms. Based on the conducted tests it has been concluded that the presence of soluble carbohydrates and the amount and form of used mycelium are the most significant factors. Shorter colonization time results in extended enzymatic feeding at the constant mycelium growing period. At the same time, loose and pliable straw creates a larger surface, which increases mushroom enzymatic activity.
2. Potential yield of fruiting bodies is determined by the mycelium mass developed in the compost. Consecutively the mycelium mass depends on a length of carbohydrate chains, that need to be degraded, amount of decay fungi in the compost and size of mycelium surface contacting compost. Cellulose, the main component in straw, is the most difficult element in enzymatic degradation. The process of starch degradation is much slower.  The increase in mass of rhizomorphic mycelium depends on the compost structure as well.
3. The temperature range of 23 – 27^oC and high CO₂ concentration support the quick compost overgrowth by mycelium.
4. The duration of the compost overgrowth process under production conditions is 12-18 days. Regardless of the unchanged length of overgrowing stage, this process can affect the yield level. In principle, a period that is too short will cause destruction in the process of biosuppresion and commensalism and there is a risk that none of them will complete. Therefore, the competing organisms will develop sooner and the temperature effect will occur. If the ingredients contained in the substrate are difficult to assimilate, the overgrowth period should be longer. Can this period be too long? A decision regarding when to end a digestion process and unwanted energy usage is difficult to make. Under the laboratory conditions mycelium mass has been growing up to 45 days.

Recolonization

It might be worthy to consider the introduction of a new term – recolonization, it is second growth of mycelium after breaking the compost removed from a tunnel or after mixing the compost on a shelf – at overgrowth phase II in production hall. This period is relatively short, 2 – 4 days and it depends on the existing temperature, water application and CO₂ concentration. Compost density is also very important. Excessive compaction of the substrate makes it difficult to increase its volume while too poor – makes it difficult to control the temperature in the substrate during shock (aeration).  Regarding further feeding, especially when introducing feeders, the control of the course of aeration is very important. Throughout this period, water is applied to the compost, and the thermal effect is controlled. Improperly applied water, along with air, low concentration of carbon dioxide in the compost and the absence or late reaction to the start of the thermal effect results in high substrate temperature increases. This causes a disturbance in feeding or in extreme cases leads to the overheating of compost.

Casing colonization

When fulfilled feeding is provided and water is well balanced in the compost, mycelium develops better and does not continue vegetative growth despite starting a shock. Thus pinning is easier. The colonization of casing and its role in feeding, particularly in cultivation without compost, and application of two layers will be examined after the establishment of a substrate content and an evaluation of substrate conditions without compost, based on fixed feeders.