Fresh, sweet, vine-ripened melons, exotic eggplant varieties and the lesser-known, fragrant pepinos are just some of the culinary delights we have come to expect from hydroponics.
While many new growers quickly advance into fruiting vine crops such as tomatoes and cucumbers with relative ease, melons, eggplants and pepinos can be a little more technically challenging for the indoor or greenhouse gardener.
Despite being well-suited to protected cultivation, these crops need more care and attention than most hydroponic plants, but their sweet rewards are worth the effort.
Tips for Growing Melons Hydroponically
Melons are a member of the Cucurbitaceae family and require the same warm temperatures and high-fruiting potassium levels as cucumbers.
Originally from Africa, they are cultivated hydroponically on a worldwide scale and can fetch premium prices in cold winter climates.
The term cantaloupe has come to mean a wide range of different melon fruit types sold in fresh produce markets, but there are distinct types.
The most commonly grown hydroponic type is the netted melon, also called a musk melon, which has a distinctive raised network of tan-gray-colored netting on the surface of the fruit.
The aromatic flesh of netted melons goes from green to salmon orange and the flesh at full maturity is sweet and succulent.
Cantaloupe melons are grown hydroponically in fields in warmer regions. They have a warty or scaly skin but are not netted, and often have deeply grooved fruit shapes that are usually orange fleshed.
Winter melons such as the honeydew are smooth-skinned and typically have green flesh.
There are also a number of specialty and heirloom melon types not commonly grown commercially that have good potential for indoor and greenhouse growers, or for gardeners looking for a small, niche-market crop.
All of these melon types have similar vine growth characteristics and nutritional, pollination, environmental and training requirements, with many of the modern, commercial-hybrid types having much more disease resistance than older types.
This is an important feature growers can take advantage of. Older melon varieties are often highly prone to mildew diseases, sometimes to the point where many plants are lost long before the fruit reaches maturity, with control difficult even with fungicide sprays.
Selecting cultivars that are resistant to mildew goes a long way towards ensuring a successful crop and minimizing the use of chemical sprays.
Melons are a warm-season crop. Their ideal temperature range is 72-90°F, with temperatures of at least 61°F at night required for good fruit set.
The plants can easily tolerate conditions as high as 93°F. Hybrid melon seed is expensive, so hydroponic growers usually sow into individual propagation cubes of media such as stonewool to avoid having to transplant.
Germination is fastest at 82-86°F, with young plants ready to place into a hydro system within two weeks. Many hydro growers make the mistake of keeping larger seedlings such as melons in their propagation trays or cubes for too long.
Root expansion from these is rapid and any root dieback during this stage can result in pythium root rot.
Once established in a hydro system, melons can be given standard vegetative and fruiting nutrient formulations, but they have a high potassium requirement when in the fruiting stages.
Supplements may be given once the plants are in active fruit expansion. These crops also have a large leaf area, which means they require high levels of oxygenation in the root zone and are more suited to a free-draining substrate than a deep-flow solution culture.
Under ideal conditions, melon plants grow rapidly. The stem will elongate and needs to be trained upwards within a week of planting out.
Melons produce tendrils that wrap around strings, other plants and other objects in their paths, so regular training is required to keep them heading in the desired direction.
Melons can be grown at a higher plant density than cucumbers or similar crops—around 4-5 plants per 3-ft.-long single row. This layout allows optimal access for pollination, training and pruning.
Melons are heavy at maturity—some reach up to 4 lbs.—and will drag the vine down if not individually supported.
Some growers use netting to support the fruits and prevent them from dropping to the floor at maturity. For high-value fruits, each fruit is supported using soft material slings or bags tied to an overhead support.
For many cultivars, this is essential to keep the heavy fruit from falling and damaging the plant. Most melon types are trained vertically to a single stem per plant with fruit produced between nodes 12 and 16.
Any side or lateral branches that form on the main stem are removed initially, and after node 12, laterals carrying flowers are permitted to form and set fruit.
Once the flowers have formed on a lateral, the stem is terminated several leaves after the position of the fruitlet, which prevents more fruit from forming on that lateral while leaving sufficient foliage to support growing fruit.
In greenhouse and indoor hydro systems, melon flowers will need to be hand-pollinated to ensure fruit set.
This process involves collecting pollen grains from the male flowers and brushing them on the insides of the open female flowers.
Female flowers can be identified by the small green melon at the base of the flower. Pollination should be carried out daily and each flower should be pollinated 2-3 times.
It’s normal if not all hand-pollinated flowers set fruit. When this occurs, the young melon yellows and drops from the plant.
Sweetness in melons is something hydroponic growers should strive for. Several factors affect sweetness, including genetics (cultivar selection), nutrition, leaf area, access to light and maturity.
Trialing different cultivars or selecting those with the highest brix levels (a measure of sweetness, with a brix level of more than 13 being a sweet fruit) is a good place to start.
Paying attention to maintaining a large, healthy leaf area and providing high light conditions will also ensure the plants produce sufficient assimilate for maximum fruit quality.
Melon fruit numbers should be limited to 3-4 per plant so each fruit receives sufficient sugars from the foliage.
Keeping EC levels within a moderately high range of 2.2-2.6 after fruit set also assists with flavor intensity.
Melons need to be harvested at just the right stage of maturity, which can be hard to gauge as little color change occurs. This stage usually occurs approximately 50-55 days after pollination.
How to Grow Pepinos Using Hydroponics
Pepinos, or South American melons, melon pears, pear melons or pepino melons, are a member of the Solanaceae family, which also includes eggplants, potatoes and tomatoes.
Pepino is Spanish for cucumber—they were first called pepino dulce (sweet cucumber) by the early Spanish explorers who encountered the plants in South America. Unfortunately, the name was shortened to pepino in English and still causes some confusion about this little-known fruit.
Pepinos are now commercially grown using hydroponics in a number of countries, although on a much smaller scale than other melon and eggplant types. They are an ideal plant for indoor gardeners wanting to produce sweet, aromatic, exotic fruit on compact, bushy plants.
The plants don’t require the space and support other vine crops must have.
Pepinos produce tear-shaped fruit, often with purple stripes, on a cream-colored skin. They are slightly smaller than cantaloupes and other melons and their flavor is more distinctive. Pepinos can be started from cuttings or from seeds.
Obtaining named cultivars from a reputable source is a good way to start out with this crop. Pepino plants have a form and leaf shape similar to a potato.
They can be kept pruned to form a compact, bush shape, or grown upwards, supported by strings and wires with regular removal of excess lateral stems.
Optimal growth occurs at 64-75°F, but pepinos are more cold-tolerant than tomatoes and are often a better option for growing environments that can’t provide the heat required by other melon types. Fruit set requires a day/night temperature differential with nights at 60°F and day temperatures exceeding 64°F to obtain good fruit set.
Commercially, pepinos are grown in a range of hydro systems and substrates, including stonewool slabs and coco fiber, with drip irrigation.
Pepinos will also grow in nutrient film technique systems provided sufficient support is given to the stems and developing fruit. Plant spacing is the same as that used by indeterminate bush tomatoes, although the plants can be kept pruned and compact when necessary.
One advantage of growing pepinos rather than other melon types is the ease of pollination—pepinos will readily self-pollinate with a little shaking or tapping of the flower truss, as is carried out with tomatoes.
Fruit sets readily and some fruit pruning may be needed to reduce the numbers after set. Unlike melons, it’s relatively easy to determine when pepinos are sufficiently ripe for harvest.
The background color of the pepino skin will change from green to yellow and the fruit will soften slightly. After harvest, the fruit should be eaten immediately or stored at 50°F.
How to Grow Hydroponic Eggplants
Like pepinos, eggplants are a member of the tomato family. A native of the subtropical areas of Asia, eggplants have been cultivated for many centuries and are now grown worldwide as a commercial greenhouse crop.
Eggplants are typically a perennial, but under hydroponic production, they are usually produced as annual bushes requiring high levels of winter heating to sustain growth and yields.
What is fascinating about eggplants is the wide variety of types and cultivars available. Fruits range from tiny, green/white spheres, to golden, egg-shaped, elongated pink/purple Japanese types, to large, black or white teardrops, all with a delicate but distinctive flavor.
These diverse types have been developed for various uses in Asian, Indian, Greek, Italian and European cuisine with many now going through a resurgence as gourmet baby vegetables.
As well as producing edible fruit, many of the more exotic eggplant types are highly ornamental with brightly colored fruits on compact plants.
Eggplants are particularly well-suited to hydroponic production in indoor spaces where heating can be maintained at high levels for the 5-6 months it takes to produce a crop.
Optimal temperatures are around 72-90°F, with a maximum of 95°F and a minimum of 64°F. An ideal seed germination temperature is within 74-79°F. For growers with limited space, smaller and more compact eggplant varieties such as golden egg are well-suited to containers as they are less than 2-ft. high at maturity.
Eggplants have similar nutritional requirements as other fruiting crops such as capsicums. Ideally, plants should be started on a balanced grow or vegetative formulation and switched to a fruiting formulation with a higher potassium level once the first fruits have set.
While the plants are self-fertile, offering some assistance by brushing pollen between flowers with a small paint brush will help increase fruit set.
Bitter flesh is an aspect of eggplants that may put people off from growing or eating the fruit.
However, while many of the older, heirloom cultivars still carry a degree of bitterness, modern hybrid cultivars have had this trait bred out of the crop, so there is no need for salting or leaching the flesh before cooking to remove the bitter compounds.
When selecting an eggplant cultivar, choosing those listed as non-bitter, and harvesting when the fruits are still young and tender will help prevent any bitterness from forming. Rapidly grown, hydroponic hybrid eggplants—if given the ideal growing conditions and harvested at the correct stage—rarely have flavor issues.
Melons, pepinos and eggplants are three of the lesser-grown hydroponic plants found in indoor gardens, and may pose technical challenges for newer growers, but with careful selection of your cultivars, and close attention to optimal growing conditions, these plants will provide you with a year-round harvest of flavorful fruit that was worth the effort of growing.