Fertilizing a hopyard with potash (potassium sulfate) in late summer and fall can enhance the winter survival potential of hop crowns and buds and ensure strong spring shoot emergence and growth. Hop plants require potassium (K) for several important physiological processes, including the creation and storage of carbohydrates in the roots and crown. Harvesting of hop bines and cones results in the removal of more K in the hopyard than any other soil nutrient. Replacement of K is critical to maintaining good plant health and yield.
Applications of potash following harvest allow hop plants to take up K during the fall period when they're going dormant and storing carbohydrates. A hop's shallow feeder root system tends to absorb K mostly heavily from near the soil surface. As a result, a hop plant can quickly absorb K fertilizers from top-dressed applications. Two split applications during the late summer and fall season help prevent the loss of K through leaching. Spring applications of potassium are far less effective in hopyards because the new shallow feeder roots are not fully in place and more leaching occurs. Cold tolerance and winter survival - and the ability to initiate and sustain spring regrowth - is highly dependent on keeping root and crown carbohydrate (sugar) reserves high. During September most hops will begin going into a dormant state and crown buds will begin to form at the base of the bines. Dormancy slows down or stops top growth and forces the accumulation of sugars in the below-ground parts of the hop plant.
One of the ways to increase hop's potential for winter damage is to cut bines too short during harvest. If you remove the energy-producing top growth completely prior to dormancy, the plant may not have adequate energy to initiate vigorous spring growth. A harvest cutting height of 2 to 3 feet is recommended for most hop varieties. Ideally, allow 6-8 weeks of top growth to remain after harvest before removing remaining bines to ensure adequate storage of carbohydrates for winter. A final fall cut bine height of 2 inches above visible crown buds is recommended. Cover any visible crown buds with a shallow layer of soil for winter protection. Read our previous post for more on minimizing crown damage.
Initial spring growth comes from crown buds formed in the previous fall, which get their energy to grow from the stored carbohydrates. These stored carbohydrates are used for initial spring emergence and growth until the hop plant has 6 to 8 feet of growth. After this primary stage, energy produced by photosynthesis and nutrients gathered by the new feeder roots fuels more rapid growth up to the wire. Potassium applied in the spring season plays a small role in primary spring emergence of the bines.
Avoid late season pot-harvest applications of nitrogen in excess of 80 to 100 pounds N/acre; this can delay proper dormancy and increase disease susceptibility. In addition to K fertility, continue to monitor the boron, zinc, phosphorus and sulfur status of the soil so the levels don't become yield limiting. Read more about micronutrients.
In conclusion, fall applications of potassium are one of the best practices to ensure a great spring start and healthy growth in your hopyard.