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The semi-dominant mutant alleleOy1-N1989encodes a dominant-negative subunit I of Mg-Chelatase that catalyzes the first committed step of chlorophyll biosynthesis. Analyses of mutant F1 hybrids from crosses ofOy1-N1989to diverse maize lines identified a natural variant atoil yellow1as major modifier of chlorophyll content. Chlorophyll reduction increased the time to reproductive maturity, decreased stalk width, and had complex effects on plant height. We explored these effects by genome wide association studies of F1 hybrids crosses ofOy1-N1989to a maize diversity panel. The delay in reproductive maturity inOy1-N1989/+ mutants neither altered the vegetative-to-adult phase change nor total leaf number but did slow the rate of organ emergence from the whorl. In addition to the allele atoy1, analysis of tetrapyrrole, heme, and chlorophyll biosynthesis pathway genes identified multiple modifiers of mutant traits. Consistent with organ emergence, rather than a developmental delay, affecting the reproductive delay ofOy1-N1989/+ mutants, known flowering time regulators did not affect variation in the reproductive delay affected by chlorophyll loss. Plant height showed a complex relationship with chlorophyll. TheOy1-N1989/+ mutant F1 plants with a modest reduction in chlorophyll were taller than their wildtype siblings, but F1 plants with dramatically decreased chlorophyll were shorter than their wildtype siblings. Perturbations in the biosynthesis of the phytochrome chromophore increased plant height in wild-type plants but dramatically reduced plant height and chlorophyll contents ofOy1-N1989/+ mutants. The mechanism by which the interaction between chlorophyll and bilin affects height and chlorophyll remains to be explored.One sentence summaryChlorophyll reduction in maize delays reproductive maturity by altering growth and not development, and depending on the reduction can either increase or decrease plant height.