Neem oil is extracted from the seeds of the neem tree (Azadirachta indica). Crude or cold-pressed oil contains azadirachtin and related limonoids, which repel insects, reduce feeding and disrupt moulting. Clarified hydrophobic neem oil has most azadirachtin removed and acts mainly as a horticultural oil, smothering soft-bodied pests and some fungal growth on contact.
In practice
Growers use neem products in veg against mites, aphids, whiteflies and powdery mildew, with thorough coverage of leaf undersides. It must never go on flowers: it leaves a strong odour and taste and oily residue on resin. It can burn leaves in heat or under strong light, and should not be combined with sulfur within a couple of weeksbeing reviewed. Products vary widely in composition, and in many places only registered formulations may be used on cannabis, whatever their natural origin. Check what is registered for cannabis locally.
Myth check
"Natural" does not mean harmless or legal. Azadirachtin is a pesticide active ingredient and is regulated as one. Label: Established.
Don't confuse with
- Horticultural oil: refined mineral or plant oil without azadirachtin.
- Neem cake or meal: a soil amendment from pressed seed residue.
A refined petroleum or plant oil sprayed to smother soft-bodied pests and eggs and suppress powdery mildew on contact; used only on foliage, never on flowers.Tetranychus urticae, the commonest cannabis mite indoors: a 0.5 mm sap-feeder that stipples leaves pale and spins webbing, breeding fastest in hot, dry rooms.Small soft-bodied sap-sucking insects of the family Aphididae that cluster on stems and leaf undersides, excrete sticky honeydew and multiply rapidly by live birth.Small white-winged sap-sucking insects of the family Aleyrodidae, mainly Trialeurodes vaporariorum and Bemisia tabaci, that fly up when disturbed and coat leaves in honeydew.A fungal disease, on cannabis caused mainly by Golovinomyces ambrosiae, that grows as white powdery patches on leaves and buds and thrives in moderate humidity.Sulfur (S) is a secondary nutrient taken up as sulfate, used in the amino acids cysteine and methionine; deficiency yellows new growth fairly evenly.Potassium salts of fatty acids sprayed to kill soft-bodied pests such as aphids, mites and whitefly nymphs on contact by disrupting their cell membranes.Contact products act only where the spray touches the pest; systemic products are absorbed and move inside the plant, which raises residue concerns in cannabis.The minimum time, set on a pesticide label, that must pass between the last application and harvest so residues fall to permitted levels.A heated vessel that vaporises elemental sulfur to suppress powdery mildew and mites in veg rooms; it carries fire, gas and timing risks and is never used in flower.
