|OSU Extension Service Crop Science Report
The hop plant Humulus lupulus L. is an herbaceous perennial, producing annual vines from an overwintering rootstock. In the spring and early summer, vines grow rapidly, winding around their support in a clockwise direction and clinging with strong, hooked hairs. They reach their ultimate height of 15-25 feet by the end of June when, in response to shortening daylength, vines stop growing vertically and produce sidearms which bear the flowers. The hop is dioecious, having separate male and female plants. Only the females produce the cone-shaped "hops" used in brewing. The male plant serves only as a pollenizer, but is not essential for the female plants to produce hop cones. Hops are heterogeneous and new plants coming from seed could be either male or female. The rootstock is an underground structure consisting of both rhizomes (with buds) and true roots (without buds) which may penetrate the soil to a depth of 15 feet or more. During the first year little growth and few flowers are produced because the plant is establishing its root system. A normal crop of hops should be expected the second year.
The hop plant produces best under specific climatic and soil conditions. A minimum of 120 frost free days are needed for flowering. Direct sunlight and long daylength (15 hours or more) is also needed. As a consequence of daylength and season length, hop production is limited to latitudes between 35 and 55 degrees. The hop plant requires ample moisture in the spring followed by warm summer weather. In dry climates the hop plant will produce best if supplemental irrigation is provided.
Soil and Plant Nutrition
A deep well drained, sandy loam soil is best. Soils with a pH of 6 to 7.5 is ideal for hop production. Poorly drained, strongly alkaline or saline soils should be avoided. Fertilizers rich in potassium, phosphate, and nitrogen should be applied each spring. Nitrogen is required at a rate of approximately 150 lbs per acre (3 lbs N/1000 ft2). The nitrogen may be applied in split applications 2 or 3 times between March and mid-July. If manure or compost is applied around the hop plant, fertilizer applications may be reduced accordingly.
The soil should be tilled to create a weed free area. A strong support system is needed for the plant to climb on. Look for space along fences, garage, or property lines. Plant in early spring once the threat of frost is gone but no later than May. The soil should be worked into a fine, mellow condition prior to planting. In cold climates you can plant rhizomes in pots and transplant in June. If planting is delayed, keep rhizomes refrigerated in a plastic bag to prevent them from drying. Plant two rhizomes per hill with the buds pointed up and cover with 1 inch of loose soil. Hills should be spaced at least 3 feet apart if the hills are of the same variety and 5 feet apart if they are different. The first year the hop plant requires frequent light waterings.
A hop quarantine in the state of Oregon prohibits hop plants and all plant parts, except kiln dried cones, from entry into the state directly, indirectly, diverted or reconsigned. There is an exception for the states of Washington and Idaho meeting specific conditions. This quarantine was established to prevent the introduction of diseases.
When the young vines are about 1 foot long, two to six vigorous vines are selected for each hill and the rest are removed. One to three vines are trained clockwise on a string which has been staked to the hill. Hops mainly grow vertically, but lateral sidearms extend from the main vine and produce flowers. The main concern is to support the vines and prevent the sidearms from tangling. Most cones are produced on the upper part of the plant.
In July, the lowest four feet of foliage and lateral branches can be removed to aid in air circulation and reduce disease development. The removal of lower leaves (stripping) must be done carefully to avoid breaking or kinking the main stem. In August allow additional bottom growth to remain to promote hardiness of the crown and plant vigor for next year.
At the end of the season you can bury healthy bottom vines for propagating new plants the next spring. Simply bury the vines in a shallow trench and mark their location. In spring dig them up and cut them into pieces about 4 inches long. Make sure each new cutting has an eye or bud.
This disease is caused by the fungus Pseudoperonospora humuli. The fungus infects only the hop plant and will not affect other garden plants. The disease first appears in the spring as infected shoots (spikes) emerge from the overwintering rootstock. The number of infected shoots may vary from none to all in any given hill. Infected shoots are stunted, brittle, and lighter in color than healthy shoots. The leaves are often deformed and curled. Infected shoots are unable to climb. Gray or black masses of fungal spores are often present on the underside of infected leaves. Spores are dispersed by wind and rain. The disease is favored by warm (65-70°F) wet weather and the fungus requires free water on leaf and shoot surfaces for infection. Spiked shoots should be removed promptly and buried.
Flowers often become infected when blooming occurs during wet weather. Young cones that are infected stop growing and turn brown. When older cones are attacked, part or all of the petals turn brown and cones fail to develop properly.
This disease is uncommon in the Pacific Northwest. Symptoms include yellow veining of the leaves and wilting of leaves and vines. Early symptoms may include wilting on only one side of a leaf. A brown discoloration inside the vine may be observed by cutting diagonally into the vine. Depending on the hop variety and the strain of the fungus, disease can vary from year to year. A plant showing symptoms this year may seem entirely healthy the next year. There are no effective control measures. The fungus can persist in the soil for several years. If this disease recurs regularly, remove the infected plant and replace with a new one in a different location
Hop plants are extremely sensitive to soil residues of the pesticides heptachlor and chlordane. Chlordane was widely used in home gardens in the l960's but both were banned in 1972. Symptoms of heptachlor and chlordane poisoning may be similar to those of Verticillium wilt but there are some important differences. The lower part of the affected vine will have a rough, scaly appearance with deep cracks which may ooze sap. Vines are brittle and may easily snap when bent. In cross-section, the central sap of the vine may have a darkened, water-soaked appearance instead of a light color. Plants will likely exhibit a slow decline over a period of 2-3 years. There is no known cure. The hop varieties Cluster and Chinook seem to be somewhat more tolerant than other varieties.
Symptoms of virus infection vary with environmental conditions. The virus may cause leaf and vine tip distortions, tip die back, yellow spotting of the leaves, stunted growth, failure to climb on the trellis and flower blasting. There is no cure and severely affected plants should be removed and destroyed. Over the years many of the most severe viruses have been eradicated from commercial production. Rootstock purchased from a reliable propagator is unlikely to have severe virus problems.
Hop aphids and spider mites are the most common hop pests. Other less serious insect pests include wire-worms, leaf rollers, armyworms, hop looper, root weevils, omnivorous leaftiers, western spotted cucumber beetles, corn earworms, and several species of cutworm. These usually are not present in damaging numbers.
Hop aphid, Phorodon humuli
The hop aphid is a small (2mm) soft bodied, pale green pest. The hop aphid overwinters on Prunus species (ie. ornamental plum trees) and in the spring return to the hop plant. Hop aphid infestations develop more rapidly during cool weather. The hop aphid does damage by sucking plant juices. Aphids should be controlled before or during flowering to keep them from entering the young cones. Once the aphids have entered the cones, they will secrete a honeydew and cause a sooty mold in the cones.
Spider Mites, Tetranychus urticae.
The adults are very small, have eight legs. They are pale green, yellowish to reddish in color, often with a dark spot on each side of their body. A hand lens is needed to see the pearly white spherical shaped eggs. The spider mite feeds by puncturing the lower leaf surfaces and withdrawing plant sap. Each puncture produces a small light colored spot. Eventually the leaves become bronzed, shrivel and die. White webs may also appear if infestation is severe. The spider mite will also feed on the petals of the cones causing them to turn brown, a condition growers call "red hops". Spider mites are a problem during prolonged periods of warm, dry weather. Mite predators include the western predator mite and the small black lady beetle. Regular washing of the plant's leaves with your garden hose may prevent an outbreak.
Cutworms over-winter as larvae or pupae in the soil. The adult moths emerge in late spring and lay eggs. The larvae that emerge from the eggs feed on plant stems at night. Cutworms can generally be found just beneath the soil surface during the day.
Prionus beetles, Prionus spp.
Adult beetles may be 1.5 to 3.5 inches long and .75 inches wide. Their long sweeping antennae may appear sawlike. Larvae are white, fleshy grubs, without legs. The head is brown with forward-protruding, very strong, jaws or mandibles. Larvae may be 1.5 to 3 inches in length. They live in the soil and feed on roots.
Hop harvest in the Pacific Northwest usually runs from mid August to mid September, depending upon the variety. If you want to use your hops for ornamental purposes, pick your hops early. Otherwise hand pick hop cones and dry them in a food dehydrator.
To determine ripeness pick a cone and touch and smell. If the cone is too green it feels slightly damp to the touch and has a softness to its scales. If you squeeze the cone it will stay compressed in your hand. A dry cone will feel papery and light. It will feel drier than a green cone, some varieties take a lighter tone as they mature. If your hands quickly take up the smell and are slightly sticky due to the yellow powdery lupulin, your hops are ready for harvest.
To harvest, cut the vine at the bottom leaving 3-4 feet of the vine to lay on the ground and cut the string at the top. Lay the vine on the ground and pick off the cones. The harvested vine can be mulched, burned, or woven into a wreath. When handling fresh hop plants wear long sleeves and gloves because the hooked hairs of the plant may cause a slight rash.
If you choose to construct a dryer, good airflow is essential, and the temperature must not exceed 140°F. Drying hops at a lower temperature takes longer, but a better quality hop is obtained. For drying the low-tech way, you can use a window screen. Spread the hops evenly across the clean screen. Place the screen off the ground and in an enclosed area to keep wind and bugs from creating problems. A healthy vine will produce 1-2.5 pounds of dried cones per plant.
The dried hops are ready for storage when springy to the touch and the yellow lupulin powder easily falls out. Another indicator is when the central stem breaks rather than bends. The stem takes much longer to dry than the petals. Cones are best stored in plastic bags that can be sealed. It is important to make sure the cones are sufficiently dry. If cones are not properly dried, they become moldy, wilted, or even rancid and cannot be used for brewing. Fill the bag until the cones are well compressed. Once the bags have been sealed and properly labeled store them in a freezer. Thawing and refreezing stored hops reduces quality and freshness.
¹Administrator, Oregon Hop Commission, Salem, OR; Extension Agent, Oregon State University, Salem, OR; and USDA, Hop Research Geneticist, Oregon State University, Corvallis, OR, respectively. EXT/CRS 104