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Azadirachta indica – neem, a versatile tree for the tropics and subtropics

FACT 97-05, September 1997
A quick guide to multipurpose trees from around the world

Azadirachta indica A. Juss. is widely known as neem, a tree that has proven value to both city and farm dwellers throughout the dry tropics and subtropics. Neem has long been recognized as a versatile multipurpose tree for urban regreening, agroforestry, fuelwood production, and for a variety of other products, including biopesticides. Azadirachta indica is a member of the Meliaceae (mahogany) family. It has been referred to in the past by the botanical names, Melia indica and M. azadirachta, which is perhaps why it is sometimes confused with a related species, Melia azedarach (chinaberry). The tree is also known as nim, margosa, limba, mimba, nimba, kohomba, and Indian lilac.

Neem is a small to medium-sized tree, with a short, straight bole. The stem branches at 2-5 m forming a broad, dense, round or oval crown. Total height is 15-25 m, occasionally reaching up to 30 m, with a stem diameter ranging from 30 to 90 cm. Neem is characterized by a long, penetrating lateral root system, which can extend up to 15 m, with a relatively short taproot. Neem has moderately thick, fissured, gray outer bark, with a reddish-brown inner bark.

It is evergreen or deciduous depending on the climate; leafless periods are usually brief, occurring during extended drought. Leaves are alternate, imparipinnately compound, 20-38 cm and bunched at the tip of branches. The tree produces many small, sweet-scented, white or cream-colored, bisexual flowers. The fruit is a smooth, ellipsoidal drupe, 1.2-2.0 cm long, containing usually one seed. The fruit is initially green and turns yellow as it ripens in about 12 weeks after full bloom. Neem trees are prolific fruit producers, starting as early as 3-5 years, and becoming fully productive at 10-12 years.

Neem adapts to a broad range of climate and soil conditions. It is normally found at elevations between sea level and 700 m. Neem can grow at altitudes up to 1500 m, as long as temperatures remain moderate, as it does not withstand cold or frost. Neem tolerates extremely high temperatures, but its normal range is about 9.5°C – 37°C. It is also highly drought tolerant, and once established, it can survive 7-8 month dry seasons. It requires as little as 150 mm rainfall per year in areas where the root system can access groundwater within 9-12 m of the surface, however, it performs best in zones receiving 450-1200 mm/year. Neem prefers deep, permeable, sandy soils, but can be planted in a wide variety of soil types, including difficult sites where most other species do not perform well. It can thrive on rocky, dry, shallow, infertile soils, but is not recommended for silty or micaceous loams, silty clay soils, saline soils, or where sub-surface hardpan or laterite outcroppings occur (NRC, 1992). Neem should also not be planted on sites where soils become waterlogged or seasonally inundated. It prefers a soil pH in the 6.2-7.0 range, but can grow within a range of 5.0-8.0 pH. Mature neem trees are light demanding, but seedlings tolerate moderate shade during their first growing season, especially on dry sites.

Azadirachta indica is indigenous to South Asia, possibly originating in northern Myanmar and the Assam region of India. Neem’s natural habitat is dry, deciduous, mixed forest, occurring in association with Acacia spp. and Dalbergia sissoo (Lemmens et al, 1995). It is widespread in India, Pakistan, Myanmar, Sri Lanka, Thailand, Malaysia and Indonesia. Neem has been introduced and established throughout the tropics and subtropics, especially in drier areas in Southeast Asia, the Pacific Islands, Australia, South and Central America, the Caribbean, sub-Saharan Africa, and the Middle East.

Agroforestry and urban forestry
. Neem plays an important role in both urban and rural landscapes. Its well-formed crown and short deciduous period has made it a popular choice for shade plantings around buildings and along roadsides. It is also used on farms as a pasture tree to shade livestock and in boundary rows. Neem is not usually selected for hedgerows or alley cropping, but is used in windbreaks and shelterbelts to protect crops from wind damage and soils from erosion.

Wood products. Neem produces a moderately dense wood, somewhat similar to mahogany. The wood has a specific gravity of 0.52-0.85, averaging 0.68 (NRC, 1992). The heartwood portion is reddish to reddish-brown, while the sapwood has a yellowish-gray or grayish-white color. The wood is hard, durable, dull to somewhat lustrous, aromatic and resistant to insects and fungi. The wood dries with only slight shrinkage, seasons well, and is easy to work, but the rough, interlocked grain does not take a high polish. Neem sawtimber is used in light construction, and to make beams, door and window frames, boxes, crates, carts, axles, yokes, cabinets, panels, boats, oars, cigar boxes, carvings, toys, drums, and agricultural implements. It is also used for furniture, especially wardrobes, book cases, and closets, because the wood repels insects. Neem trees are often managed under pollarding or coppicing systems to produce posts and poles. The roundwood is also used as fuelwood and makes very good charcoal. At 14% moisture content the wood gives an energy value of 16.92 megajoules/kg (Lemmens, 1995).

Non-timber products. Useful products can be harvested from almost every part of the neem tree. The bark produces tannins, a fiber used to make rope, and a resin used to make glue. Bark is used medicinally as a remedy for fever, and fruit pulp is also used as a tonic. Leaves are used as mulch and green manure, and can also be used as fodder. The leaves have a crude protein content of 12-18%, but because they have a bitter taste, livestock usually prefer other foods. Neem leaves mixed in with stored grain have traditionally been used in India to repel insects and prevent food and seed losses.

Azadirachtin. The principal active compound in the leaves is azadirachtin, which repels pests, acts as an antifeedant, and disrupts insects’ growth and reproduction. Several bioactive compounds are found in the leaves and other tissues, however, the neem seed kernels are the main source of azadirachtin. Neem seed contains the most concentrated and accessible amounts of other potentially useful compounds as well. Neem-based pesticides have already been approved for various applications and are being produced commercially in several countries. Low-tech methods have also been developed to produce neem extracts. These methods will be described in a future FACT Sheet.

Neem oil and neem seed cake. Neem seeds will yield 40-50% oil when the dry kernels are crushed or pressed through an oil mill. Neem oil is used as fuel for lamps, an antiseptic for animal wounds, a lubricant for machinery, an insect repellent, to remove tobacco suckers, and in the production of soap, toothpaste and cosmetics. It has also traditionally been used for a variety of medicinal purposes, but there is evidence that it should not be ingested orally. Neem oil may also have potential in the development of pesticides and fungicides, although it does not contain azadirachtin (NRC, 1992). Neem seed cake is the residue left after the oil has been extracted from the kernel. Neem cake is used as a fertilizer with insecticidal and fungicidal effect.

. Neem seedlings can be produced vegetatively by air layering, cuttings, grafting and tissue culture, however, they are usually grown from seed in nurseries as bare-root stock or in containers. Direct sowing is more cost-effective, but may result in poor survival in drier zones. Neem wildlings are an inexpensive source of seedlings, as natural regeneration is normally abundant. Although neem is a prolific seed producer, seed supply is frequently a problem. The viability of fresh seed decreases rapidly after two weeks, and improperly stored seeds have low germination rates. Ripe seed should be collected from the tree and processed immediately. First the pulp is removed and the seeds are washed clean. Seeds are air dried for 3-7 days in the shade, or until the moisture content is about 30%. They can then be stored for up to four months if kept at 15°C. Seed will remain viable even longer if dried to 6-7% moisture content and refrigerated in sealed containers at 4° C.

Sow seed in nursery beds in rows 15-25 cm apart, and 2.5-5 cm spacing within the rows. Seedlings can be pricked out when two pairs of leaves have developed (1-2 months), or the rows should be thinned to 15 cm x 15 cm spacing. Plastic pots are commonly used to produce neem seedlings, although rigid container systems are used in Haiti with success. Seeds should be sown horizontally at a depth of 1 cm. Fresh seeds will have the highest germination rate, and seedlings will emerge within in 1-3 weeks. Removal of the seed coat may increase germination rates for stored seeds. Both bare-root and containerized seedlings should be raised under partial shade for the first 1-2 months, or until about 30 cm tall, then gradually exposed to full sunlight.

Bare-rooted seedlings are usually kept in the nursery for 1-2 years before outplanting. The roots and shoots of seedlings lifted from nursery beds should be pruned before transplanting. Bare-rooted seedlings can also be prepared for stump planting. Stumps are made from 1-2 year old seedlings by trimming the root to 20-22 cm root and the shoot to 5 cm. Containerized seedlings should be outplanted after 3-4 months in the nursery, when they reach 30-50 cm. Fuelwood plantations are laid out at a 2.5 m x 2.5 m spacing, and then later thinned to 5 m x 5 m. The recommended spacing for windbreaks is 4 m x 2 m. Neem trees managed to maximize fruit yield should be more widely spaced to allow the crown to develop fully.

Management. Young seedlings suffer from weed competition, but weed control is usually only needed during the first growing season. Neem seedlings should also be protected from fire, although mature trees can recover from fire damage. Once the root system is well-established, early growth is rapid for about five years, then slows gradually. Neem responds well to coppicing and pollarding to produce poles, posts, or fuelwood. Coppicing to produce fuelwood is managed on a 7-8 year cycle. Pollarding is used to manage windbreaks, and to produce posts. Yields vary greatly depending on site conditions, but fuelwood production reports range from 6-57 m3/ha/year.

Azadirachta indica has few serious pests or diseases. The most serious insect pests are scale insects, including the neem scale (Palvinaria maxima) and the oriental yellow scale (Aspidiotus orientalis), both of which can cause considerable damage. The oriental yellow scale has been associated with a widespread neem defoliation in West Africa in the mid-eighties, although severe drought may have previously weakened the trees (NRC, 1992). In the early 1990’s another neem die-back in West Africa was reported. This was at first thought to be caused by a soil fungus, but after several years of observation, no specific pathogen or pest was identified. The cause of the disorder is now believed to have been stress-related due to low soil moisture brought on by extended drought and soil compaction.

Selected References

Lemmens, R.H.M.J.; I. Soerianegara and W.C. Wong (Eds.), 1995. Plant Resources of South-East Asia No 5(2). Timber trees: Minor commercial timbers. Backhuys Publishers, Leiden. 655 pp.

National Research Council, 1992. Neem: A Tree For Solving Global Problems. National Academy Press, Washington, D.C.

Randhawa, N.S. and B.S. Parmar, 1993. Neem Research and Development. New Delhi: Society of Pesticide Science, India.

Read, Michael D. and James H. French, eds. 1993. Genetic Improvement of Neem: Strategies for the Future. Proc. of the International Consultation on Neem Improvement held at Kasetsart University, Bangkok, Thailand, 18-22 January, 1993. Bangkok, Thailand: Winrock International. 194 + x pp.

Written by Carol Stoney, Program Officer, Winrock Internationa;

A publication of the Forest, Farm, and Community Tree Network (FACT Net)