New plants are created via plant propagation of which there are two types: sexual and asexual.
With sexual propagation, there are two sources of parental DNA resulting in the creation of a third living organism. Sexual propagation involves the floral components of the plant and is the result of the pollination of megagametophyte (egg). There are two types of sexual reproduction.
The first is open pollination, in which the seed produced will be identical to the genetically identical parent plants. Such plants have been inbred (see also the purpose of plant breeding and selection and why it is a never-ending story) to propagate the best qualities of a given variety. All heirloom plants are open-pollinated.
The second form of sexual production is hybridization which occurs when two plant varieties are crossed to produce offspring with the best genetic traits of each parent plant (ex. one variety has powdery mildew resistance and one is drought tolerant). The F1 (first) generation plant will exhibit the positive effects of the inter-breeding. However, the following generations (F2, etc.) will produce unpredictable offspring.
Success in sexual propagation is not guaranteed and largely dependent on appropriate temperature, water, light, and oxygen levels. For example, if the temperature is too high, it is likely that the blossoms will drop preventing fertilization and ultimately reproduction. Sexual propagation is considered the more cost-effective form of propagation. Likewise, it is a way of preventing the transference of disease from the parent plant to offspring.
Asexual propagation occurs when a piece of a parent plant is removed from the parent plant and regenerates to create a new plant that is genetically identical to the parental plant. Such a form of propagation can be considered cloning. Common methods include grafts, separation, dividing, layering, and cuttings.