Accessible, reliable and diverse sources of climate information are needed to inform anticipatory responses to climate change at all levels of society, particularly for vulnerable sectors such as smallholder farming. Globally, many communities use Indigenous knowledge (IK) and local knowledge (LK) to provide contextually calibrated and trusted forecasting information to guide livelihood choices, including on-farm decisions by smallholder farmers. Here, we examined the role of IK and LK in seasonal forecasting, preparedness, and broader climate adaptation decision-making of smallholder farmers in Chiredzi, Zimbabwe. Data was collected from 100 smallholder farmers through face-to-face semi-structured interviews in the month before the rainy season onset when preparatory decisions about planting were being made. Seventy-three percent (73%) of the interviewed farmers are using IK and LK-based climate forecasts, and 32% (of 73%) farmers rely on IK and LK only for climate risk preparedness decision-making. Binary logistic regression found the use of IK and LK climate forecasts by farmers was strongly predicted by farmers’ age and farm size with p = 0.009 and 0.017 respectively at p < 0.05 significance level. Farmers using IK and LK forecasts are implementing, on average triple, the number of adaptation measures compared to farmers not using IK and LK. These findings emphasise the accessibility and reliability of IK and LK for seasonal forecasts and demonstrate the close link between use of IK and LK and the implementation of adaptation actions. Recognition, inclusion and preservation of IK and LK are important to ensure its potential role in informed responses to climate change.