Competition is one of the more important forces shaping biological communities in nature. Although much research has investigated how traits influence competition, uncertainty remains concerning the importance of competitor trait similarity on competition. An experiment was conducted using Arabidopsis thaliana natural accessions expressing varying degrees of similarity in several traits to investigate the influences of trait similarity, intra- vs. inter-accession interactions, and nutrient availability on competition. Results showed that more similar competitors did not experience more intense competition. Additionally, intra-accession competition was not consistently stronger than inter-accession competition. I found that trait differences in size and growth rate among accessions were better predictors of competitive outcome than competitor trait similarity. I also found that increasing soil nutrients had little effect on competition beyond increasing overall plant size and fruit production. This study highlights the capacity for ecological systems to deviate away from what might be predicted by generalized theory.