Understanding events is fundamental to remembering them later, but it remains unclear how incoming information is linked to prior knowledge. We investigated whether episodic memory encoding depends on semantic control processes that allow people to use their knowledge in a flexible and task-relevant manner. We manipulated semantic control type and demand at encoding to compare the contributions of two key processes: controlled semantic retrieval and semantic selection. In two preregistered experiments, young adults studied object images in two semantic encoding tasks. They matched the object either to the word most related in meaning out of three (controlled retrieval) or the word most similar in size (semantic selection). We then tested participants’ memory to see whether these semantic control processes affected concept-level item recognition, specific old-lure discrimination (Experiment 1, N = 78), and source memory (Experiment 2, N = 64). The results revealed that controlled semantic retrieval at encoding improved concept-level recognition compared with semantic selection but did not impact specific memory. Although encoding judgements were slower under greater control demand (image-word semantic similarity indexed by word2vec), demand did not significantly impact later memory on any measure. We then used a hierarchical Bayesian multinomial processing tree model to estimate source memory parameters. This revealed better source memory detection following encoding with controlled retrieval compared to semantic selection. Together, the results show that memory representations are shaped by the semantic control processes engaged at encoding and suggest that controlled semantic retrieval may be a key contributor to elaborative semantic encoding.