According to Wikipedia, "Phenology is the study of periodic plant and animal life cycle events and how these are influenced by seasonal and interannual variations in climate, as well as habitat factors." In English, phenology studies the way plants and animals interact with seasonal changes in the environment.
Nothing exists in isolation. Our skin is covered with a thousand different types of bacteria, with a population close to a trillion. These critters help protect us against pests and diseases. Plants exist in the same way. There are microbes whose very existence relies upon the presence of a single plant variety's stamen. There are other bacteria that allow plant roots to absorb nitrogen.
As with all other living things, these microbes and bacteria are prey to larger, more complex beings. If these predators arrive too soon, or too late, they will starve, as will their predators, and so on.
Plant DNA contains a series of instructions on how to create the various parts of the plant and how to accomplish specific processes within the plant. As each plant part is developed, it is subject to external conditions: soil composition, temperature, humidity, sun exposure, rainfall, the presence of pollinators, and countless other variables that we have yet to identify.
One simple way to learn more about your local phenology is to collect the first fall leaf from your yard and record the date. As years pass, you will see trends and changes as other factors are altered.
You can learn more about Phenology here.
I hope this information inspires you to grow more of your own food. You can ask your garden questions on my Home page.