The pollen source in a given area depends on the type of vegetation present and the length of their bloom period. What type of vegetation will grow in an area depends on soil texture, soil pH, soil drainage, daily maximum and minimum temperatures, precipitation, extreme minimum winter temperature, and growing degree days. The plants listed below are plants that would grow in USDA Hardiness zone 5. A good predictor for when a plant will bloom and produce pollen is a calculation of the growing degree days.
