The baobab fruit shells were evaluated for their suitability as a substrate for growing oyster mushrooms and compared to three base substrates (wheat straw, maize cobs, and sawdust) of 1 kg dry weight. The duration of developmental stages, mycelium vigor, yield, and biological efficiency of the oyster mushroom from the four different substrates were recorded. Yields from the first 3 harvests (flushes) were considered, as they were the most productive ones. Wheat straw demonstrated significantly ( p < 0.05 ) higher mycelial colonization rate taking an average of 23 days to complete full spawn run followed by baobab fruit shells, sawdust, and maize cobs which took averages of 25.8, 27.2, and 29.5 days, respectively. Baobab fruit shells had the longest number of days taken between full spawn run and first pinhead formation with an average of 14.4 days which was significantly different ( p < 0.05 ) to the wheat straw, sawdust, and maize cobs which had 7.4, 9.4, and 10.5 days. The highest yield was observed on the sawdust which had an average of 682 g followed by wheat straw with 594 g. Maize cobs and baobab fruit shells had the least yield of 518 g and 482 g, respectively. The results showed that baobab fruit shells could be used as a substrate for the cultivation of oyster mushrooms and it can be recommended for commercial cultivation of oyster mushrooms.

Disposal of spent mushroom substrate (SMS) generated after mushroom cultivation is a subject of great concern. Unplanned disposal causes land, water, and air pollution together with the nuisance in the surroundings. During recent years, environmental legislation has forced mushroom growers to think about more amicable ways of SMS disposal. Hence, farmers in different corners of the country are using SMS as manure for various field crops and horticulture but without any support of the recommended rates from scientific data and therefore may not be getting the optimum benefits. This study sought to evaluate the effects of spent mushroom substrate on the yield and quality of baby spinach. The experiment was conducted in Mazowe, Zimbabwe, with 5 treatments (10 t ha−1, 20 t ha−1, 30 t ha−1 of SMS, and two controls) arranged in a CRBD and replicated 3 times. Biomass production (fresh mass, dry mass, root length, fresh root mass, and dry root mass) and sensory evaluation were determined 35 days after planting. Results showed that increasing rates of spent mushroom substrate significantly ( p  < 0.05) increased the fresh yield and quality of baby spinach. Application of spent mushroom substrate beyond 30 t ha−1, however, increased the bitterness of baby spinach. The results of the study present the potential of the spent mushroom substrate as an organic fertilizer for the production of quality baby spinach.