Plant Selection for Push & Pull Systems in Hydroponics
Strategic Companion Plants for Pest Control (also in pots nearby)
General Considerations for Plant Selection
The effective design of a Push & Pull system requires careful selection of companion plants. These should not only be able to repel or attract specific pests but also thrive in their respective environment. When companion plants are placed in separate pots next to the hydroponic system, many restrictions regarding root systems and nutrient management are eliminated, significantly expanding the selection. Below, plants are sorted by the pests they influence, and it is indicated whether they are suitable for the hydroponic system itself or a separate pot.
1. Aphids (Aphidoidea)
Push Plant: Basil (Ocimum basilicum)
Function: Repellent.
Properties: Releases essential oils (eugenol, linalool) that deter aphids.
Placement: Ideal in hydroponics or in a pot nearby. Moderate feeder, shallow root system.
Push Plant: Garlic (Allium sativum)
Function: Repellent.
Properties: Sulfur compounds are unattractive to aphids.
Placement: Better in a pot nearby, but also possible in hydroponics (needs firm anchorage). Light feeder, shallow root system.
Pull Plant: Nasturtium (Tropaeolum majus)
Function: Attraction (as a trap crop).
Properties: Aphids prefer nasturtium over many crops.
Placement: Very good in hydroponics or in a pot nearby. Moderate feeder, shallow root system. Regular removal of infested plant parts is crucial.
Pull Plant (Beneficials): Dill (Anethum graveolens)
Function: Promotes beneficial insects (ladybugs, hoverflies, parasitic wasps) that eat aphids.
Properties: Provides nectar and pollen for beneficials.
Placement: Good in hydroponics or in a pot nearby. Light feeder, deep root system.
Pull Plant (Beneficials): Coriander (Coriandrum sativum)
Function: Promotes beneficial insects (hoverflies, parasitic wasps, lacewings) that combat aphids.
Properties: Flowers attract beneficials.
Placement: Good in hydroponics or in a pot nearby. Light feeder, shallow root system.
2. Whiteflies (Aleyrodidae)
Push Plant: Marigold (Calendula officinalis)
Function: Repellent.
Properties: Produces pyrethrins and other repellent chemicals.
Placement: Better in a pot nearby. Light feeder, deep root system.
Push Plant: Catnip (Nepeta cataria)
Function: Repellent.
Properties: The contained nepetalactone acts as a strong repellent for many insects, including whiteflies.
Placement: Good in a pot nearby. Light feeder, shallow root system.
Pull Plant: Cardamom (Elettaria cardamomum)
Function: Attraction (as a trap crop).
Properties: Whiteflies are attracted to cardamom; can serve as a "sacrifice crop".
Placement: Only in a pot nearby (requires special conditions). Light feeder, deep root system.
3. Spider Mites (Tetranychidae)
Push Plant: Mint (Mentha spp.)
Function: Repellent.
Properties: Menthol and menthone have repellent effects.
Placement: Good in hydroponics (control root system) or in a pot nearby. Moderate feeder, shallow root system.
Push Plant: Coriander (Coriandrum sativum)
Function: Repellent.
Properties: Its scent compounds can deter spider mites.
Placement: Good in hydroponics or in a pot nearby. Light feeder, shallow root system.
Pull Plant: Pole Bean (Phaseolus vulgaris, specific varieties)
Function: Attraction (as a trap crop).
Properties: Spider mites prefer beans as a host plant.
Placement: Only in a pot nearby. Heavy feeder, deep root system. Infested plants must be removed regularly.
4. Fungus Gnats (Sciaridae)
Push Plant: Rosemary (Salvia rosmarinus)
Function: Repellent.
Properties: The strong scent of rosemary (essential oils like cineole, pinene) can repel fungus gnats.
Placement: Good in a pot nearby. Light feeder, deep root system. Moderately possible in hydroponics.
Push Plant: Geranium (Pelargonium spp.)
Function: Repellent.
Properties: Many geranium species release substances that repel insects.
Placement: Only in a pot nearby. Light feeder, shallow root system.
5. Thrips (Thysanoptera)
Push Plant: Marjoram (Origanum majorana)
Function: Repellent.
Properties: The essential oils can deter thrips.
Placement: Good in hydroponics or in a pot nearby. Light feeder, shallow root system.
Pull Plant: Candytuft (Iberis umbellata)
Function: Attraction (as a trap crop).
Properties: Certain Iberis species attract thrips.
Placement: Only in a pot nearby. Light feeder, deep root system.
General Beneficial Insect Promotion (independent of specific pest)
Pull Plant (Beneficials): Fennel (Foeniculum vulgare)
Function: Promotes beneficial insects (ladybugs, hoverflies, parasitic wasps).
Properties: Umbelliferous flowers are an attractive food source.
Placement: Better in a pot nearby (requires more space). Moderate feeder, deep root system.
Pull Plant (Beneficials): Yarrow (Achillea millefolium)
Function: Promotes beneficial insects (ladybugs, lacewings, predatory bugs).
Properties: Attractive to a wide range of beneficials.
Placement: Only in a pot nearby. Light feeder, deep root system.
Pull Plant (Beneficials): Buckwheat (Fagopyrum esculentum)
Function: Promotes beneficial insects (especially hoverflies and ladybugs).
Properties: Flowers quickly and provides abundant nectar and pollen.
Placement: Good in hydroponics (as a fast-growing, short-lived beneficial magnet) or in a pot. Light feeder, shallow root system.
Important Notes for Hydroponics & Companion Planting
- Nutrient Management: For plants directly in hydroponics, pay attention to nutrient requirements and adjust the nutrient solution if necessary. Light feeders are often easier to integrate. For potted plants, separate fertilization is possible.
- Root Management: Plants in hydroponics with aggressive root growth must be controlled. Potted plants elegantly solve this problem.
- Regular Monitoring: All plants, especially trap crops, must be regularly checked for pest infestation. Heavily infested trap plants should be removed or treated specifically before they become a breeding ground.
- Light Requirements: Ensure all companion plants receive sufficient light to perform their function.
- Experiment: The effectiveness of Push & Pull systems can vary depending on specific conditions (climate, pest pressure, main crop). Experiment with different combinations to achieve the best results.
Common Pests in Hydroponics by Main Crop
Knowing the typical pests for specific hydroponically grown crops is crucial for the proactive planning of an effective Push & Pull system. This list provides an overview of common pests to expect depending on the main crop, along with associated symptoms.
Leafy Greens (e.g., Lettuce, Arugula, Spinach)
- Aphids: Small insects on leaf undersides and young shoots. Sucking damage, honeydew, growth disorders.
- Whiteflies: Small, white, flying insects, often on leaf undersides. Sucking damage, honeydew, yellow spots.
- Fungus Gnats: Small, black gnats swarming around plants. Their larvae can damage fine roots.
- Thrips: Tiny, elongated insects leaving silvery trails and discoloration on leaves.
Herbs (e.g., Basil, Mint, Coriander, Parsley)
- Aphids: Very common, especially on young shoots. Leaf deformation.
- Spider Mites: Fine webbing on leaf undersides, small yellow speckles on leaves.
- Whiteflies: Can occur on various herbs, especially with denser growth.
- Fungus Gnats: Common in moist substrates or damp root zones.
Fruiting Vegetables (e.g., Tomatoes, Cucumbers, Peppers, Strawberries)
- Whiteflies: One of the most persistent pests, leading to growth depression and honeydew.
- Spider Mites: Often cause significant damage, with webbing and leaf discoloration (silvery-bronze).
- Thrips: Can damage flowers and fruits, leave silvery scars on leaves.
- Aphids: Can occur on young shoots and flowers, especially on tomatoes and peppers.
- Leafminers (e.g., Liriomyza spp.): Larvae feed tunnels (mines) in leaves, reducing photosynthesis.
Root and Tuber Vegetables (e.g., Radishes, Carrots, Radish)
- Aphids: Can infest above-ground leaves and weaken plants.
- Fungus Gnats: Their larvae can damage young roots and the tuber itself.
- Brassica Pests (for brassicas like radishes): Include cabbage flies and aphids.
Citrus Plants (if cultivated hydroponically)
- Aphids: Infest young shoots and leaves.
- Whiteflies: Commonly found on citrus leaves.
- Scale Insects / Mealybugs: Fixed, scale-like or woolly formations on branches and leaves, sucking damage, honeydew.
- Spider Mites: Can occur in dry climates.
Important Note:
This list provides general guidance. Actual pest infestation can vary depending on region, greenhouse conditions, hygiene, and introduced pests. Regular monitoring is always the best strategy to identify problems early and take action.
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