Sweet, aromatic dessert or table grapes are a luxury fruit that often receives premium prices and home-grown vines can produce heavy yields over a short harvesting season.
Hydroponic grape production is not a new concept; grapes have long been grown in greenhouses and there has been recent interest in the development of soilless vineyards. Like many fruiting plants, grapes respond well to the controlled nutrition and climatic advantages of protected cultivation and produce high-quality fruit with an intense, sweet flavor and aroma.
While grape vines can become large with an extensive canopy, they are able to be heavily pruned to restrict size and fit into compact spaces. Indoor garden environments also provide the warm, bright, and humidity-controlled conditions that allow for easy production and prevention of the common fruit-rot diseases that often affect outdoor grown fruit.
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Grapes are climbing vines and need wires, strings, or trellis to train the stems upwards and support the weight of the developing fruit. In an indoor garden, a grape vine container can be positioned in a corner while the vines themselves are trained and held against walls or up over supports to maximize the use of growing space.
Grapes are also a fruiting plant that benefits from some root zone restriction and can be grown in surprisingly small containers. Dutch buckets or growing containers of at least 1.5 feet in depth are suitable for well-pruned grape vine production, filled with a free draining substrate such as perlite or a coco fiber/perlite mix.
Drip irrigation is commonly used for hydroponic grape production and provides a good level of moisture, while at the same time allowing for some dry down of the substrate between irrigations; this assists with the production of fruit with a high compositional quality and optimal sugar levels.
One of the main advantages of hydroponic grape vine production is grafted plants are not required as the soil-borne pests and diseases that can severely affect the vines are not present in soilless cultivation.
Cuttings can be taken of any good dessert grape variety and, once roots have formed, established into a hydroponic production system. Hardwood cuttings from healthy vines are typically taken in late fall or winter from outdoor-grown plants as grapes do not grow true to type from seed.
New buds will start to sprout in spring after roots have formed and at this stage the new young plant is ready to establish into a hydroponic system, alternatively young vines can be purchased and the growing medium carefully removed before planting.
There are a huge number of different grape varieties ranging in fruit size, color, and sweetness and with subtle differences in flavor. Table or dessert grapes are commonly white, black, or red in color, however, green types also exist with popular greenhouse varieties that are suitable for indoor gardening being Black Hamburg, a well -flavored, dark-skinned type and Chasselas, an early season grape that produces well in pots.
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Training and pruning are essential for indoor grape vines — without suitable growth restriction and control, hydroponic vines can become extremely vigorous and soon lead to jungle-like conditions within a confined space. There are a few different methods of grape vine training, however, for greenhouse and indoor spaces either the cordon or fan method work well.
The fan system involves training shoots that develop from the main stem up against a wall with two trained out vertically and one horizontally, these are then cut back to just two to three buds per shoot; numerous new shoots will then form that can be selectively trimmed to give an attractive fan shape.
The cordon method of training is simpler, takes up less space, and involves allowing just one or two stems to develop that are trained into position. From these stems, side shoots will develop (eventually these become the spurs), which have the growing point removed two buds from the permanent stem. Grapes and leaves are produced on these side shoots that are cut back each year, building up a fruit spur and keeping the vine compact.
As part of the training process, any excess tendrils should be removed as they form. Tendrils are thin, twisted stem-like growths the plant uses to cling and climb as it scrambles up over surfaces. Tendrils can get tangled up with the fruit bunches and are best removed to allow the training system to support the plant and prevent the plant’s assimilate being diverted away from developing fruit production.
Apart from supporting the vine and fruit, along with regular training and pruning to maintain vine shape and restrict vegetative growth, dessert grapes often benefit from some thinning of the fruit bunches. Commercially produced greenhouse grapes are thinned to not only create a perfectly shaped and uniform bunch, but to also increase the average size of the berries; sweetness is also improved with thinning. Thinning is best done when the grapes are still very small and with long-bladed scissors (avoiding touching the surface of the grapes helps to retain the bloom on the surface of the fruit).
Pollination and Growing Conditions
Indoor-grown grapes will need some pollination assistance in much the same way as tomato flowers require hand pollination or stem shaking to release the pollen. Pollination can be achieved by shaking the flowering stems vigorously or by stroking each bunch of flowers to cause pollen transfer. Alternatively, a small brush can be used on the flowers for the same purpose.
Grape vines need similar amounts of light and day length as other fruiting vines like tomatoes and cucumbers. The environment needs to be warm with optimums of 72-82°F (22-28°C) suitable and avoidance of high humidity particularly when the vines are in fruit and prone to rot diseases. Good levels of air flow up and under the canopy are also required, and training of shoots should facilitate air circulation around the developing grape bunches. Grapes require a cold winter dormancy period as part of the life cycle — this is usually achieved by cutting the vine back after fruiting and taking the containerized plant outdoors to overwinter.
Read also: Pollinating in Greenhouses
Grapes respond well to hydroponic nutrition, however, sometimes a little too well, and rapid and excessive vegetative growth can be common in many varieties. While training can help contain growth, the nutrient solution EC can be used to assist with the process. Running high EC levels or restricting irrigation so the substrate dries down between irrigations can be used to both restrict vegetative growth and increase the compositional quality of the grapes by concentrating sugar levels.
During the fruit development phase, a standard hydroponic bloom or fruiting nutrient product or formulation with high potassium levels will assist yield and fruit quality while maintaining high light levels will ensure the plants produce sufficient assimilate for high brix (sugar levels) fruit and maximum flavor. Electric conductivity levels in the 2.0 –2.4 range are suitable for young vines with EC level up to 4.0 for those in fruit.
Some care needs to be taken with irrigation, however, as excess moisture levels or irregular watering during the late-fruit developmental stages can cause fruit to split. Irrigation should be gradually reduced during the fruit-ripening stages to help prevent this from occurring.
Harvesting Hydro Grapes
Grapes are a fruit that need to be fully ripened on the vine to achieve maximum flavor and sweetness. For dessert varieties, sampling a few fruit when fully colored will determine when they are sweet enough to harvest. A hand-held brix meter, to measure fruit sugar levels, is also a useful tool for assessing when to harvest table grapes.
Bunches should be cleanly cut from the plant with scissors and not pulled form the vine as this can cause tears and stem damage. Grapes that appear to be slow to mature and color can benefit from some additional heating during this stage, particularly at night.
Pests and Diseases
Indoor grapes are prone to the same pests as many other fruiting vines such as tomatoes, including whitefly, aphids, mealy bugs, and occasionally mites under low humidity conditions. The main issue with some grape varieties is fungal pathogens, specifically mildew and botrytis (grey mold). Mildew can be devastating on grape vines and lead to defoliation. The main method of control is growing resistant varieties and using a good rate of ventilation and air movement under and through well-pruned vines. Protectant fungicide sprays can also be used for mildew control.
Botrytis or grey mold mainly affects the ripening fruit under conditions of high humidity and causes fruit rot and development of grey-brown, ash-like spores that spread the disease as they are released into the air. Botrytis is largely a cool-season pathogen and suitable levels of heating, humidity control, ventilation, and air movement are the main methods of prevention.
A well-controlled, pruned, and trained grape vine can make a valuable addition to a growroom and be trained up against a suitable wall or over tall supports. The quality and flavor of the fruit under hydroponic nutrition and in an optimal environment can be far superior to outdoor-grown fruit with opportunities to maximize sweetness and grape size by manipulating factors such as EC, nutrients, moisture levels, and climate.