Determining the maturity of compost and other organic fertilizers is very important because of possible phytotoxic or phytostimulative effects. The maturity of the compost can be assessed on the basis of chemical analyses, and the germination test with different test plants is most often used to determine phytotoxicity. In this research, using the results of chemical analyses, the maturity of compost produced from plant residues after maintenance of green public areas was assessed. At the same time, a germination test was carried out with 4 test plant species (cucumber, garden cress, triticale, barley) to determine the phytotoxicity of compost (i.e. compost extract in a ratio of 1:2.5 and 1:10) and 3 ammonium N solutions (in concentrations of 200, 400 and 600 mg/L NH4-N). According to the chemical properties of compost, primarily the C/N and NH4-N/NO3-N ratios, as well as the NH4-N concentration, and the germination test with cu-cumber and garden cress, we can conclude that the tested compost was mature and that we do not expect a phytotoxic effect. The choice of the plant is very significant because the germination test with compost extract shows an undoubted phytostimulative effect on garden cress and cu-cumber with more pronounced phytostimulative effect of compost 1:10 than 1:2.5 extract. No such effect was found on the monocotyledonous test plants triticale and barley since the 1:10 ex-tract had no significant effect, and the 1:2.5 extract had a phytotoxic effect, moderate on triticale and high on barley. The conclusion is that garden cress and cucumber are suitable test plants for determining phytostimulative effect of compost, but they are not suitable for determining phytotoxicity for monocotyledonous plants, especially if the cause of phytotoxicity is some non-ammonium component. Barley is the most suitable species for determining non-ammonium phytotoxicity of compost and phytostimulative or phytotoxic effect of ammonium form of nitrogen. It would be very useful to conduct a comparative germination test with compost extracts in the ratio 1:2.5 and 1:10, whereby the 1:2.5 extract is used as a test for phytotoxicity, and the 1:10 extract for testing phytostimulative effect.