Hops are not a crop that is routinely associated with hydroponics — a tall vining plant produced on an extensive scale outdoors in suitable temperate climates for the brewing industry. Despite seeming to be an odd specimen for greenhouse or indoor cropping, hops have, in fact, become one of the new, innovative options for growers looking to produce a niche market product. For those who have a liking for craft beers or inkling to brew their own, growing a few hop plants can be a viable option as well as a fascinating new crop to experiment with.
The hop plant (Humulus lupulus) has a long history of cultivation and is primarily grown for the production of dried or pelleted hop flowers (cones) which are used to add bitterness, flavor, and aromatics to beer. However, the fresh hop cones (called wet hops), which have a very limited storage life, can also be used in brewing and may confer additional qualities that the pelleted form does not. Commercial wet hop brewers typically aim to use the fresh cones within 48 hours of harvest for maximum compositional quality and will pay a premium price for such a niche market crop. For homebrewers, the potential of producing selected varieties of hops specifically for wet-hop brewing immediately after harvest has become an exciting possibility as fresh hops are often difficult or impossible to obtain.
The harvestable portion of the hop plant are the flowers (also called cones or strobiles).
The harvest season for outdoor grown hops is extremely short and only occurs once a year, however, hydroponic hop crop experiments suggest three to five crops per year of fresh cones may be possible with the use of climate control under protected cultivation. With successional planting, it could be possible to supply high-quality fresh crops throughout the year from hydroponic production. There have been reports that with the controlled nutrition in hydroponics, hops with higher concentrations of essential oils, aromatic compounds, beta acids, and flavonoids can be produced as well as larger, heavier cones and a higher overall yield.
Apart from their essential use in beer brewing, hops have other properties of interest. These include medicinal compounds that can act as a mild sedative for the treatment of insomnia. Hops pillows — pillow fabric filled with dried hop cones — have long been used to help induce sleep, while other compounds have been used to treat anxiety and restlessness. Other hop products include tea and soft drinks, and the tips of the young shoots can be steamed and eaten in a similar way to asparagus. Hops are also occasionally used in culinary dishes for a unique flavoring or to add a distinctive aroma.
Varieties of Hops
There are a number of modern commercial varieties of hops bred for specific uses, as well as many older, general purpose heirloom types. Popular varieties include Cascade, Chinook, Columbus, Magnum, and Centennial, each with different compositional qualities. Research into hydroponic hops has shown that Cascade and Chinook are suitable varieties for small-scale hydroponic production and perform well under greenhouse production. The Cascade variety is the most widely utilized by craft brewers in the US and is used in the production of many types of ale and some lagers. With a high alpha acid content (4.5-6 percent) and pleasant citrus-like aromatic quality, Cascade is a general-purpose hop variety well suited to hydroponic production
Hop cones are produced on long bines (vine-like stems) which support the plant by clinging to support structures.
Hops are relatively easy to grow as they are extremely vigorous and heavy feeders that benefit from the controlled nutrition of hydroponic systems. Hops produce separate male and female plants, with only the female plants producing cones, thus hop propagation is typically carried out vegetatively to ensure only female plants are grown. If male flowers are present in a hop crop, the pollination of the female flowers results in seeds that are undesirable for brewing beer. For small-scale growers, hops are typically obtained during the dormant winter season as short sections of rhizome containing a number of dormant buds. Once planted into warm conditions, rhizomes establish quickly and produce several young shoots. Hop cuttings can also be taken from established plants that will produce roots readily at leaf nodes without the requirement for any rooting hormone application. At certain times of the year, young potted hop plants are available for purchase. Once growth has begun, the hops produce long, climbing shoots termed called bines that develop short, stiff hairs along the stem surface, allowing the bine to cling and climb upwards (vines, on the other hand, use tendrils or other means to cling to surfaces). This rapid upward growth of the bines requires support, and hydroponic hops are well-suited to being grown on training systems similar to those used for tomato and cucumber crops. Tomahook tomato support systems — overhead wires with strings or trellis — may be used to support hops and plants will readily climb and cling with no assistance. Since hop plant bines grow to considerable length and height, for indoor and greenhouse production the “lean and lower” system of training, commonly used for commercial tomato crops, appears to work well. As the bines increase in height, the supporting string is detached and lowered along the floor or lower levels of the cropping area as required. Alternatively, the tops of the bines can be trained vertically along supports at the top of crop, or allowed to grow upwards, and then trail back down towards the floor.
Greenhouse-grown hops may be grown for year-round production of `wet hops’ for the craft beer industry.
As with other larger hydroponic plants, hops are best grown in a drip-irrigated system with at least two gallons of a free draining growing substrate, such as perlite or coarser grade coconut fiber, as they are intolerant of wet feet, particularly in the early stages of growth. Nutrients should initially start with a high-quality, general purpose vegetative formulation at an EC of 1.8–2.2 with a high ratio of nitrogen to potassium. During the later stages of growth, this can be switched to a flowering/fruiting formation with higher potassium and phosphorus levels, as well as gradually increasing the EC during the cone production stage to maintain high levels of essential oils and other compounds that constitute the quality of the flowers. Hops are a warm season crop; during the active growth phase, the crop requires light of similar intensity to tomato, cucumber, and pepper crops. Good air flow is essential, particularly around the lower levels of the plant where high humidity can promote disease. While vigorously growing hop bines under ideal growing conditions are relatively problem free, they can be prone to mite infestations in warmer, drier conditions. Early detection and ongoing control is advisable as mites can cause considerable crop damage. Powdery mildew may also be a concern in some hop varieties, particularly where air flow is insufficient around a dense canopy.
Under good growing conditions, cones will develop along the bines in succession and ripen at slightly different times. For this reason, hand-harvesting ripe cones from the bines and leaving immature ones to develop further can be carried out on a small scale. Determining harvest ripeness can take some experience, but mature cones will appear plump, full sized, soft and dry, lightweight, slightly paler or yellow in color, and will have developed a high level of fragrance. Immature cones are generally greener, firmer, and compact and can be left to ripen on the plant. For larger scale hop crops, all the bines can be cut back and removed at harvest for easier cone removal leaving three to four feet at the base of the plant for regrowth. Once harvested, the fresh cones can be used immediately, however, shelf life is relatively short, and the quality can decline rapidly under warm conditions. Fresh cones can be stored in the refrigerator for a few days if necessary but are best used within 24 hours. Most fresh hops, once removed from the vines, are rapidly dried to maintain quality. On a small scale, this can be done by laying the cones in a cool, dry place, out of direct light for several days until fully dried. These can then be stored in vacuum sealed bags either under refrigeration or in the freezer before use.
Young hop shoots produced by an underground rhizome system which is used for propagation.
Hydroponic hops production may be a relatively new trend and an unusual plant for protected cultivation, but their value is in the demand for high-quality fresh cones that are best used within a day or two of harvest. With a wide range of cultivars to select from and several different training system possibilities, hydroponic hops are a crop that has a promising future.