As asparagus spears age after harvest, shoot fibers can lignify and toughen, and their flavor can change from sweet to bitter. Spears should therefore be harvested when immature. To allow plants to develop strong, healthy tops, wait until the second year after planting to harvest spears. Limit harvest to two weeks in the second year and one month in the third year after planting. From the fourth year after planting, you can harvest in Minnesota from early May to late June. Yields should increase up to the seventh year after planting, then stabilize until plants are fifteen or more years old. Overharvesting one year will decrease the following year's yield by reducing plant vigor and draining sugar reserves in the crown.Harvest spears 6 to 9 inches in length by cutting or snapping the spears. If using a sharp knife to cut the spears, tilt the knife 45 degrees to the soil surface and cut the spears at ground level or 2 inches below the soil surface. Cutting below the surface may damage spears that have not yet emerged, but leaves a woody base that may restrict water loss and slow the entry of decay organisms.Because spears are harvested when actively growing, their respiration rates are very high. Reduce respiration by harvesting when temperatures are cool (early morning or evening), shading field boxes or bins, and cooling spears to 34 degrees F immediately after harvest, preferably by hydrocooling.