10 Worst Plants for Aquaponics

Aquaponics has changed the way many progressive nations grow nutritious leafy greens and herbs. Many salad vegetables, such as lettuce and arugula, are now commercially grown in technologically-advanced aquaponic systems. There, the plants are provided with rich nutrient concentrations, well-structured artificial light regimes, and a relatively pest-free environment. In turn, they aid in recycling water for the growth of fish.

While these self-sustaining conditions seem perfect for many species, allowing them to grow rapidly and produce high-quality leaves and fruits, their limitations can be problematic for slow-growing and large crops. Some plants are therefore better suited than others for even the most high-budget setups. Many aquaponics technicians tend to stick to plants that specifically require the nutrients found in fish waste.

In an aquaponic system, the basic needs of both fish and plants need to be compatible. For example, it wouldn’t make sense to grow plants that thrive best in markedly acidic conditions; low pH levels may kill the fish stock and impede the production of beneficial bacteria. Herbs that grow exceedingly quickly, requiring heavy upkeep and frequent harvests, may also be less profitable in the long run. If you’re new to aquaponics, you’ll want to steer clear of the plants below.

1) Chrysanthemums (Chrysanthemum spp.)

Known for their impressively-sized and eye-catching inflorescences, chrysanthemums are some of the most popular ornamental plants for flower production. Their blooms are a staple addition to bouquets and floral arrangements for just about any occasion, so many cultivars are now intensively grown in flower farms. Apart from being visually appealing, they bring a number of beneficial services to modern-day gardens.

Unfortunately, though growing these plants can be quite straightforward given the appropriate substrates, they are highly incompatible with most aquaponic systems. Chrysanthemums thrive best in porous substrates with slightly alkaline conditions. This makes it difficult to find plants and fish that can be grown alongside them.

For aquaponic systems to be economically viable, their yield should at least make up for the energy costs of plant production and maintenance. Mainly, the most valuable part of these plants is their blooms which, to be produced in high densities, require a combination of trace macro and micronutrients. Deficiencies in calcium, sulfur, and magnesium, elements that may be naturally low in aquaponic systems, can lead to minimal or anomalous bloom production.

2) Blueberries (Vaccinium spp.)

Berries are generally difficult to grow in aquaponic systems as they are highly competitive. When grown alongside other species, they are known for aggressively competing with them for space and nutrients. Shrubs that can grow to about 3 – 8 feet (0.9 – 2.4 meters) tall in optimal conditions, they need ample space to mature and eventually produce fruit. This drastically limits how many fruit-bearing plants can be produced in a small space.

Apart from being markedly competitive, blueberries can be difficult to cultivate in aquaponic setups as they require low pH levels to assimilate high amounts of nutrients. Acidic conditions below a pH of 6 can be quite harmful to many fish species. The plant itself may grow in neutral conditions, but it may fail to produce a desirable yield of fruits.

More reasons to avoid growing blueberries in an aquaponic setup are their susceptibility to fungal or viral infections and their tendency to produce shallow and fine root systems. If many of these plants are grown alongside one another, they may attract a number of pests that can be difficult to remove from their complexly intertwining and woody shoots. As their root systems are shallow, propagation via plant division is limited.

3) Grapes (Vitis spp.)

It’s challenging enough to successfully grow grapes in fully sunlit and expansive vineyards. Growing these vines in an aquaponic system, with limited space, would be a feat to behold. These plants would require a special setup with a trellis or arbor-like contraption to keep their lengthening shoots and heavy fruits supported. A single plant would require about 9 feet of square footage and may take years to mature into a fruit-bearing specimen!

Fully-grown grapes are taxing to maintain as their vines may spread as far as 50 feet (15 meters) away from the main plant. The sheer weight and nutrient requirements of these can make aquaponic grape production unprofitable. A great portion of the nutrients goes into shoot and branch production alone. Similarly, a considerable amount of investment would go into maintaining structural support.

Be prepared to wait for years before the first few fruits manage to develop. Despite the abundance of nutrients in an aquaponic system, grape vines need to have well-established and extensive root systems to gather all the necessary nutrients for fruit growth. The thought of an aquaponic grape farm may seem lovely, but it simply may not be worth it unless you have an excess of resources.

4) Mint (Mentha spp.)

Although mint is one of the best herbs to grow in gardens and around pond systems, its ease and rate of growth are precisely its drawbacks in aquaponics. This rapidly growing plant, which comes in dozens of species and valuable hybrids, can outgrow its place in no time. With high availability of nutrients, its shoots can grow as much as 48 inches (122 cm) tall, towering over nearby herbs. Its suckering roots can spread out indeterminately.

If you cannot commit to regularly harvesting and pruning your mint stalks, it would be best to cultivate slower-growing herbs like parsley and chives. These are less prone to choking your system, leaving more room and nutrients for other valuable crops. Without proactive maintenance, excessively tall and bushy mint plants may also attract pests and diseases.

Nonetheless, if you have ample experience with aquaponics or are in need of an herb that can be grown in a low-light area, you may try your hand at growing mint. It remains to be one of the most rewarding herbs to grow due to its many uses in the garden. While the blooms attract pollinators, the leaves produce essential oils that can repel many pests. Of course, they are also infinitely useful in the kitchen.

5) Potatoes (Solanum tuberosum)

While it is definitely possible to grow root crops in an aquaponic system, it requires a more advanced understanding of media beds and a more careful approach to water maintenance. To stabilize the crown of potato plants and make room for optimal root growth, a bed filled with peat, pebbles, or ‘hydroton’ (clay balls) is necessary.

Apart from requiring a more complex media bed compared to those for most types of herbs and leafy greens, potatoes will require cool conditions and slightly acidic water (pH 5.5 – 6.5). This range can be detrimental to many types of fish, making it tricky to select economically viable species to be grown alongside potatoes. At pH levels below 6, beneficial microbes may struggle to aid in nutrient cycling.

The above-ground features of potatoes can be quite deceiving, especially as a particularly productive shoot does not always equate to plentiful tubers. Keep in mind that, with potatoes, it’s what’s in the ground that counts. When nutrient conditions are suboptimal, vegetative structures can continue to lengthen and eventually outgrow the setup without producing valuable tubers. The same goes for sweet potatoes, which may shift their energy toward producing more leaves instead of tubers in an aquaponics system.

6) Onions (Allium cepa)

Another root crop that may be tricky to grow in an aquaponic setup, the common onion requires special conditions and a wicking bed or floating raft system to produce high-quality bulbs. Its roots must be kept in a porous substrate that can periodically be flooded and drained with nutrient-rich water. To maintain a desirable growth rate, temperatures need to be kept at around 12 – 25˚C (54 – 77˚F). Outside of this range, the bulbs may either fail to sprout or may grow too quickly.

A major challenge to growing onion bulbs with nitrogen-rich water is their sensitivity to nitrate concentrations. An excess of nitrates can affect the color and photosynthetic efficiency of the leaves, resulting in bulbs with suboptimal flavor. The nitrogen, zinc, and potassium levels will need to be monitored and tweaked occasionally. Deficiencies in other trace elements, such as iron, may also cause crops to fail.

Although fish waste can typically provide onions with all of the necessary nutrients for growth, there’s no guarantee that they’ll lead to favorably-sized bulbs. You can’t directly observe the bulbs’ rate of growth or fully examine them until the intended harvest date. This would definitely be challenging for anyone with a novice-level understanding of onion production.

7) Ginger (Zingiber officinale)

Known for its strikingly strong flavor, ginger is a popular root crop with an array of medicinal and culinary uses. It is one of the most challenging plants to grow in an aquaponic system and is best left to the experts! This crop takes at least 10 months to produce rhizomes of harvestable size. With roots that can spread to about 3 feet (91 cm) wide in the appropriate growth medium, they take up space that more cost-efficient and rapidly-growing crops may use.

To successfully produce high-quality ginger roots, the media bed can’t be submerged in water. Soaked roots can quickly become rotten, preventing further growth and making them unsuitable for consumption. An aquaponic design that simply hydrates the growth medium and allows for thorough drainage (such as a flood-and-drain setup) is necessary.

Ginger shoots and leaves have the tendency to sprawl over the media bed and prevent other plants from getting ample sunshine. This doesn’t necessarily mean that their root systems have just as wide coverage and are producing favorably-sized rhizomes. Like onions and potatoes, the roots are tricky to maintain as they simply cannot be fully examined until the harvest date. Moreover, additional nutrients and trace elements may be required for good growth.

8) Peppers (Capsicum spp.)

Peppers may be difficult to grow in aquaponic systems because they require consistently warm and humid (65 – 60%) conditions. In temperate countries, they will need to be located in a greenhouse setup, where their shoots are well-protected from the cold until they can produce their edible and spicy fruits. It takes around 5 or more months for well-established shoots to begin to produce fruits.

Capsicum roots need to be exposed to water that is 16 – 21˚C (61 – 70˚F); markedly higher water temperatures can cause the fruits to become deformed. The water’s pH also needs to be regulated and kept at 5.5 – 6.5, a range in which some types of freshwater fish may struggle to thrive. The media bed will have to be stripped of limestone to prevent spikes in pH levels.

Apart from temperature and pH maintenance, nitrate levels would need to be constantly checked. Although peppers are not the most demanding plants in terms of nutrients, they will require more than just nitrates to produce fertile blooms and high-quality fruits. You may need to supplement your system with phosphorus and potassium. A sturdy supporting structure, which would take more labor and resources to install, would also be necessary to support the fruits as they grow.

9) Corn (Zea mays)

While it is definitely possible to grow corn in an aquaponic system, it is far from straightforward and easy! This valuable crop has many needs, many of which can only be met with a mature setup. As it is a warm-season crop, it thrives best in air and water temperatures between 25 – 32˚C (77 – 90˚F). The shoots and leaves need to be exposed to at least 8 – 12 hours of full sunlight each day, a requirement that is difficult to meet in naturally lit and indoor setups.

Even if your stalks of corn are able to produce inflorescences, there’s no guarantee that they’ll develop into fruits. One of the reasons why growing corn can be so demanding is that they may require hand pollination in the absence of wind. The hand pollination process can take a few days to a full week. As an alternative method, you may opt to use strong fans to blow pollen from the male corn tassels toward the female corn silks.

Apart from requiring several rows of corn to increase the chances of successful pollination, aquaponic cultivation of this species can attract many pests to your system. Monocultures of corn are prone to being infested with earworms, corn smut, Stewart’s wilt, and rust. These can ruin the quality of the fruits and cause overall stunted growth.

10) Melons (Cucumis melo)

Now present in an impressively diverse array of cultivars, melons come in all shapes and sizes. The most commonly grown types are the cantaloupe, muskmelon, and honeydew, all of which are known for their sweet flesh and tough rind. An annual herb that favors warm climates and rich substrates, C. melo is normally cultivated as a climbing or trailing plant. It is a tricky plant to grow in an aquaponics system due to its demand for space, light, and a supporting structure.

Melons can take a lot of time to mature into fruit-bearing vines. Initially, the shoots and leaves thrive on a continuous supply of nitrates. Over time, the roots may need to be supplemented with phosphorus and potassium, which are necessary for flower and fruit production. As an aquaponic system is meant to be cyclical and self-sustaining, the necessary addition of these nutrients makes it less cost-efficient.

Growing melons in an aquaponic system can also be more labor-intensive as the growing vines will require more and more support over time. Once fruits begin to appear, the supporting structures will need to be reinforced to reliably bear their weight. Melons that have been harvested from an aquaponic system, even one with supplementary nutrients, compromise the protein contents of the fruit.