Common name: Neem

Neem is a handsome tree native to India, Sri Lanka, and Myanmar (Burma), valued for the medicinal and insecticidal properties of its leaves, fruit, and seed.

Moderately fast-growing, it may reach up to 25 m (82 ft) tall under ideal conditions. However, it is typically a medium-sized tree, 10 to 15 m (32 to 50 ft) tall, with a straight trunk supporting a densely leafy, rounded crown. The bark is dark grey to grey-brown, smooth on young trees, becoming vertically furrowed and rough with age.

Leaves are large, up to 40 cm (1.3 ft) long and fern-like, consisting of dark green, toothed and sharply pointed leaflets arranged in pairs along the length, occasionally with an extra leaflet at the tip. These emerge bronze-red, become dark green with age, and remain on the tree where the dry season is short, but fall where it is long and pronounced to conserve water.

Flowers are small, five-petaled, white, and sweetly scented, reminiscent of honey. They are borne in short, branching clusters arising at the leaf base and come into bloom in the dry season.

Fruit oval, up to 2 cm (0.8 in) long, green when young, becoming orange-yellow when ripe, and with fleshy pulp surrounding a single seed, which has an oily kernel inside.

Grand Cayman, Cayman Islands

Material uses

Natural insecticide - Seed extracts are valued for their antifeedant and insecticidal properties and are used as a "soft" pesticide to protect crops against destructive insects without harming the wider environment. Unlike conventional pesticides, which kill insects on contact or shortly after, Neem's chemicals control insect populations by interrupting larval development: Azadirachtin, the principal insecticidal constituent, prevents larvae from forming a new cuticle after shedding the old one, and also acts as an antifeedant, inhibiting insects from feeding and growing. It effectively controls a range of chewing and sucking insects, including whitefly, moth larvae, mites, aphids, and related organisms, though its delayed action compared to synthetic pesticides can disappoint those expecting instant results, making Neem harder to promote as an effective pesticide.

Azadirachtin is commercially extracted from dried, ground seed kernels using a solvent, usually methanol - a step performed either before or after oil extraction - and is found mainly in the meal rather than the oil, at concentrations of 2 to 4 mg per gram of kernel. Cold mechanical pressing of the kernels also yields 30 to 50% of a brownish-yellow oil, traded as "Neem oil" or "Margosa oil," which is itself used as a spray-on horticultural oil, particularly against sucking insects such as aphids.

Natural insect repellent - The seed extracts are also valued for their repellent properties.

Natural fungicide - Neem oil is also used as a fungicide against powdery mildew, black spot, and rust; it's rated organic, meaning it can be used safely up to the day of harvest.

Natural soap - Neem oil is also highly valued in India for its antiseptic and medicinal properties, including in medicated soaps.

Natural shampoo - And shampoos.

Natural skin care - As well as ointments and liniments.

Natural cosmetic - And cosmetic creams and lotions. Current research also suggests it holds promise as a natural preservative in food, pharmaceuticals, and cosmetics, though this use isn't yet established.

Biofuel - Neem oil has also been successfully engine-tested as a biodiesel. Mature trees produce, on average, around 50 kg (110 lbs) of fruit per season, and the kernel - about 19% of the fruit by weight - yields roughly 45% oil; this equates to about 4.3 kg (9 lbs) of neem oil per tree, or the equivalent of 4,300 kg of neem oil per hectare (3,836 lbs per acre), assuming a planting density of 1,000 trees per hectare (400 trees per acre).

Hardwood - Neem wood is medium-weight, averaging about 650 kg per cubic metre (40 lbs per cubic ft), placing it in the durable hardwood class.

Decay- and rot-resistant wood - It also has moderate to high natural resistance to rot, decay, and wood-boring insects, making it suitable for indoor and some outdoor construction. The heartwood is reddish-brown, lustrous, and attractively mottled.

Timber and lumber - It is sawn into lumber.

Furniture and cabinets - Used mainly for furniture and general construction.

Firewood - Neem wood also makes good firewood, with a high calorific value; it coppices well, which has led to it being grown specifically for this purpose.

Natural gum - The trunk exudes, without wounding, a pale yellow to amber gum with properties similar to that of Gum Arabic (Senegalia senegal), for which it is sometimes used as a substitute.

Environmental uses

Foliage ornamental - Neem is widely cultivated as an amenity tree for its attractive form and showy, feathery foliage.

Street tree - It is often planted in India as a street or roadside tree.

Livestock browsing resistant - Because the leaves contain high levels of the toxin saponin, cattle and other ruminants do not readily browse them, giving the trees a greater chance of survival where these animals are allowed to roam freely.

Bee forage - The flowers are reported as a major honeybee nectar source in India, particularly in the states of Uttar Pradesh and Maharashtra. However, they are less important as a pollen source.

Edible uses

Honey - The honey is lightly golden, thin, runny, and slightly bitter.

Health uses

Natural dental care - Neem oil's antiseptic properties are also valued in oral-care products such as toothpaste and gargles. The seed's antiseptic properties are also present in smaller amounts throughout the rest of the plant, including the twigs, which in some areas of India and Southeast Asia are broken off and used as disposable toothbrushes.

Neem oil and other extracts can also treat skin ailments such as scabies and acne.

Climate

Neem grows naturally in sub-humid to moderately humid subtropical and tropical climates, generally frost-free areas with annual lows of 16 to 25°C, annual highs of 25 to 37°C, annual rainfall of 500 to 3500 mm and a dry season of 3 to 8 months.

Growing

New plants are usually started from seed, which loses its viability quickly and should be sown within two weeks of harvesting the fruit from the tree.

Neem trees perform best on free-draining clay-loam, loam and sandy-loam soils of a slightly acid to moderately alkaline nature, generally with a pH of 5.0 to 8.5, and on sites with full sun exposure.

It has poor tolerance for flooding, waterlogged or slow-draining soils, which can cause the taproot to rot. Reports on the tree's tolerance to saline soils conflict, ranging from generally intolerant to highly tolerant, with estimates of up to 10 grams of dissolved salt per litre of water.

Problem features

Fruit-eating animals and birds disperse the seed, sometimes far from the parent tree. Neem is classed as an invasive species in Australia, a term applied to the most serious weeds of the environment and agriculture. The tree also tends to sprout suckers from the roots.

Books

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Articles, Journals, Reports and Working Papers

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