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Biochar, a carbon-rich material resulting from pyrolysation, is one of the proposed alternatives as a substrate component to peat. The aim of this study was to investigate the effect of different ratios of peat substitution with a locally available hardwood biochar on the chemical characteristics of growing media, seed germination, plant morphological and nutritional parameters of Tagetes patula. Experimental results show that biochar can be used as a partial peat replacement, showing a complementary liming effect, rising the initial pH of peat (2.8) to values of 4.5 and 7.3 in mixtures with 50% and 75% substitution of peat by biochar, respectively. The mixture with a 50% biochar rate exhibited the strongest change between initial and final pH, rising from 4.5 to 5.7. Increasing content of biochar in the mixtures corresponded to increasing content of total K, Ca, Mg, available K and decreasing level of available Mg. The highest germination percentage was observed in the mixtures with biochar rates from 50% to 100%. Among all substrates, the greatest plant diameter, true leaf area and total root length were measured in the 50% peat substitution mixture, where the highest contents of P, K and Ca in plant shoots were found.

The objective of the research was to investigate the effects of pine bark, fresh grass and peat mulch on the ornamental value of Petunia × atkinsiana, Impatiens walleriana and Tagetes patula cultivars during the short growing period, and soil chemical properties (electrical conductivity, pH, organic matter, total N, P, K, Ca, Mg) and soil moisture in the second year in a temperate climate. Results show that fresh grass and peat mulch increased plant height of Petunia and Impatiens from 40 days after planting until the end of experiment. During the same period plant diameter of Impatiens and Tagetes was enhanced in all studied mulches, but plant diameter of Petunia was enlarged only with peat mulch. Impatiens number of flowers enhanced in all mulches, but in case of Tagetes the number was higher with pine bark. In comparison with unmulched treatment, soil moisture, electrical conductivity and pH increased in fresh grass and pine bark treatments. Soil Mg content was higher up to 15% in plots with fresh grass mulch. Plant diameter of all species was positively correlated with soil electrical conductivity.