Hereditary variation is a vital component in the development of new and improved cultivars of landscape plants. Sources of hereditary variation include naturally occurring variation, recombination due to controlled crosses, artificial mutagenesis, and genetic modification via biotechnology. Here I explore all methods with the exception of genetic modification via biotechnology. In Acer I evaluated naturally occurring cytometric variation. Cytometric variation refers to variation in genome size and ploidy. Genome size and ploidy data can be used in the development of targeted breeding projects including interploidy hybridization. I used flow cytometry and traditional root squashes to measure genome size and determine ploidy. Chemical mutagenesis through the application of ethyl methane sulfonate was utilized to induce hereditary phenotypic variation in Ornithogalum candicans (cape hyacinth). Phenotypic variation was evaluated by collecting field data of mutant seedlings. Interspecific hybridization through controlled crosses was evaluated as a method to increase phenotypic variation in Sections Dasanthera, Saccanthera, and Penstemon of Penstemon.I found that there is indeed natural ploidy and genome size variation in Acer. Genome size and ploidy data collected in this survey will add to the growing body of knowledge relative to angiosperms. Additionally, the identification of natural polyploids will be of use in developing breeding programs focused on sterile cultivar development. Ethyl methanesulfonate is an effective means of inducing phenotypic variation in Ornithogalum candicans and was shown to lead to a reduction in both plant height and fertility. Interspecific hybridization of sections of interest in Penstemon has some challenges. Challenges include identifying the appropriate environment for controlled crosses and ascertaining the fertility and crossability of target species and garden cultivars used in breeding germplasm.