Currently, biochars are produced from a wide range of feedstocks with a broad diversity in physicochemical characteristics. Therefore, a diverse agronomic response of crop plants to biochars application was expected. A preliminary ecotoxicological assessment is necessary before application of biochar to soil, even though biochar is a recalcitrant carbon considered as a promising soil amendment because of its ability to climate change mitigation by sequestration of carbon in the soil. Thus, a Petri dish germination test was conducted to assess the effects of six walnut shell biochar rates (i.e., 0, 10, 20, 40, 80, and 120 Mg ha−1) on seed germination and early growth of seedlings of fodder crops (Triticale cultivar X Triticasecale Wittmack and Pisum sativum sp. arvense L. varieties Taşkent and Özkaynak). A simple Petri dish bioassay method used to determine the effect of biochar rates on seed germination. Germination rate decreased with both higher and lower rate of biochar application. Results showed that the germination rate and growth indices were dependent on plant species. The seed germination rate of all three species was stimulated at the 40 Mg ha−1 rate, but Taşkent mung bean occurred at the highest rate of 120 Mg ha−1. Significantly higher germination rate and growth indices observed with the 40 and 80 Mg ha−1 biochar rates, respectively. Biochar application generally increased seed germination at rates ≤ 40 Mg ha−1 and seedling growth indices at rates ≤ 80 Mg ha−1. This rapid test can be used as the first indicator of biochar effects on seed germination rate and early growth of seedlings. Farmers could use this test before investing in biochar application.