In the Northeast, hop harvest generally begins in mid-August and continues through mid-September. Harvest date is primarily dependent on the hop variety but weather can delay or hasten maturation and impact when harvest will occur. In addition to weather, various pests, such as spider mites and downy mildew, can similarly impact harvest timing. The time at which you harvest hops can affect the various qualities of your finished product. Alpha and beta acid content peaks before many essential oils have fully developed. Delaying harvest can provide time for these oils to develop but increases the amount of time the hops are left vulnerable to disease and fall rains which can result in degradation of resins.
Vermont, University of Vermont
Darby, Heather; Bruce, John; and Lewins, Scott, "Hop Harvest Timing" (2017). Northwest Crops & Soils Program. 58.