The natural capacity of peatland ecosystems to regenerate after a disturbance by peat mining is often a long-lasting process. However, some plants have an ability to colonize, stabilize the peat surface and cope with harsh environmental conditions. Here, we studied ecological factors helping to explain niche separation of two grass species Holcus mollis and Deschampsia flexuosa, which have colonized peat deposits soon after the peat extraction ended in a post-mined peatland (South Bohemia, Czech Republic). While H. mollis, a creeping growth-like plant, formed lawns in dry parts of deposits, D. flexuosa, a tussock forming plant, colonized wetter parts. This implies that microhabitat conditions, most importantly soil moisture, may influence niche separation. The diversity of other less abundant vascular plants was the highest in lawns of H. mollis and low in an open vegetation dominated by D. flexuosa. The roots of the two studied grasses were colonized by arbuscular mycorrhizal fungi in a similar rate which suggests that positive associations are essential for plants to set up in harsh conditions of post-mined peatlands.