High soil temps above 95 degrees can seriously damage the fine shallow root feeder system of hops. Damage from excessive heat usually shows up a few days after it actually occurred - the plants stall and even wilt; even though the soil moisture is there. This problem is especially prevalent in newly established hopyards with wide row spacing Where the plant canopy doesn't provide soil shading..
Growers often compound their problem of high temperature damage by turning on the drip irrigation at mid-day. The temperature of the water in a black emitter tube line laid on soil in direct sunlight can reach scalding temperatures. With the low flow rates of most emitter systems a grower can easily apply a gallon of 120 degree (or more!) water to each plant in the yard. This effectively sautees the fine shallow feeder roots - disaster!
Watch out for this pattern - the hops bines get progressively shorter and yellower away from the main feed.
Solution: Watch the temperature forecast. FINISH all irrigation cycles by mid-morning. RESIST the temptation to turn on the irrigation at mid-afternoon! (In an emergency, open the end caps on the dripper lines and flush them until you feel the water temperature drop).
Consider adding some aerial sprinklers - which is the proper way to cool an overheated hopyard. Run them in short cycles before mid-day as cold water applied to hot leaves causes damage.
Setting up your hopyard for an expected scorcher of a day is easy to do - just do it early! Mis-use of your watering system causes further plant damage, stalling of growth, and kills your yield potentials.
Lynn, the head hop grower at Great Lakes Hops has over 30 years of experience in the horticultural field. Browse the blog articles here to find useful growing information for humulus lupulus, based on personal experience and observations at Great Lakes Hops.