Greenhouses extend seasons but concentrate pests. Organic management keeps your protected crops clean and market-ready.
Greenhouse Advantage: Physical Barrier
Excludes mammals (rabbits, voles), birds, and many flying insects. But aphids, whitefly, spider mites, thrips, fungus gnats, and caterpillars still arrive—on plants, tools, vents, or you.
1. Companion Planting (In-Ground or Pots)
| Companion | Repels / Attracts | Placement |
|---|
| Marigold (Tagetes) | Nematodes, whitefly, aphids | Border rows, interplanted |
| Nasturtium | Trap crop for aphids; attracts hoverflies | Perimeter pots |
| Chives / Garlic | Aphids, spider mites | Near tomatoes, peppers, cucumbers |
| Basil | Thrips, flies, mosquitoes | Throughout |
| Alyssum | Attracts parasitic wasps, hoverflies | Bench edges, hanging baskets |
2. Organic Sprays (Test First!)
- Soap Spray: 1 tsp castile soap/gal water → test 2 leaves → wait 24h → scale to 1–3 Tbsp/gal. Spray tops & bottoms weekly.
- Neem Oil: 1–2 tsp/gal + soap emulsifier. Disrupts feeding/molt. Evening only.
- Horticultural Oil: Suffocates eggs, scales, mites. Dormant or summer weight.
- Bt (Bacillus thuringiensis): Caterpillars only. Specific, safe.
- Diatomaceous Earth: Dust soil surface for fungus gnats, slugs.
3. Scouting & Mechanical Control
- Yellow sticky cards (1/1000 sq ft) — monitor whitefly, thrips, fungus gnats, aphids.
- Hand-remove: Squish aphid colonies; pick caterpillars; vacuum whitefly (shop vac + soapy water).
- Remove heavily infested leaves/plants immediately.
- Sanitize: Clean benches, tools, pots between crops. Solarize soil (clear plastic, 4–6 weeks summer).
4. Beneficial Releases (Preventive)
- Encarsia formosa (parasitic wasp) for whitefly.
- Phytoseiulus persimilis (predatory mite) for spider mites.
- Aphidius colemani for aphids.
- Release at first sign; repeat per supplier schedule.
Organic greenhouse IPM = vigilance + habitat + targeted action. Clean crops, clear conscience.
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