Long-term potentiation (LTP) is thought to be a key plasticity mechanism underlying the formation and maintenance of hippocampal place codes. It is unclear, however, which properties of these neural codes are inherited from upstream processing and which are learned through plasticity. To disentangle these influences on place codes, we utilized a method for abolishing LTP specifically in hippocampal region CA1 of the adult mouse without affecting basal synaptic processing: conditional genetic deletion of a necessary component of the postsynaptic membrane fusion machinery, Syntaxin3 (Stx3). Surprisingly, most hippocampal dependent behaviors were spared by Stx3 deletion. However, mice lacking CA1 LTP did not express typical novel environment preferences. By imaging calcium activity of CA1 neurons during a novel environment virtual reality behavior, we find that LTP is not required to form stable neural representations of context and space. This result is accounted for by a simple computational model that predicts stable CA1 codes can be passively inherited from upstream CA3 inputs. This model also correctly predicts differences in place field properties between mice with and without LTP such as place field width and the number of place fields per cell. Expanding on this hypothesis, LTP is necessary for endowing population codes with the properties that are unique to CA1 but not present in CA3. First, LTP is required for the overrepresentation of reward locations. Second, LTP is necessary for the experience dependent backward shift of place fields in novel environments. Third, LTP is essential for the increased population activity in novel environments. Collectively, these results suggest that LTP in CA1 serves a unique role in processing reward and novelty, but its role in spatial coding may most often be to augment existing biases in presynaptic connectivity.