Alstonia (Devil's Tree / Blackboard Tree) in the UAE

The alstonia, known as the blackboard tree or devil's tree, is a fast-growing evergreen widely planted across the UAE for quick, dense shade. Its neat tiers of glossy leaves, arranged in distinctive whorls around the branches, give it a layered, almost architectural look that suits avenues, park edges and larger villa gardens.

It has one notorious quirk. In the cooler months the tree produces clusters of small greenish-white flowers with a powerful, heavy scent that many people find overwhelming — pleasant to some, headache-inducing to others. It is worth knowing about before you plant one near bedroom windows or a seating area.

This guide covers growing alstonia well in UAE conditions — watering in litres, the right coconut coir mulch depth, feeding on alkaline sand, the flowering-scent issue, pests and a full seasonal calendar.

Overview

Botanical name: Alstonia scholaris. Family: Apocynaceae (the same family as frangipani and oleander, and like them it exudes a milky latex when cut). Native to tropical South and Southeast Asia and Australasia, it suits the UAE because it grows quickly, holds its leaves year-round for constant shade, and tolerates heat once established. Its common name, the blackboard tree, comes from the soft, pale wood historically used for writing boards.

Alstonia's strengths are speed and evergreen density — it delivers usable shade faster than most trees here and keeps it through winter. Its quirks are the strongly scented cool-season flowers, the milky latex that can irritate skin, and a root system vigorous enough that it should be kept a sensible distance from paving and structures. It also needs more water than true desert species and can suffer iron chlorosis on the alkaline soil. Sited thoughtfully — away from windows and hard surfaces — it is a reliable, good-looking shade tree for landscaping and larger gardens across the emirates.

Water Requirements

Alstonia is more moisture-demanding than desert natives, reflecting its tropical origins, so it needs consistent water to keep its dense evergreen canopy healthy. In peak summer (June–September) give a mature tree roughly 70–120 litres per week, split into two or three deep waterings. In winter (December–February) reduce to 30–50 litres every 10–14 days, enough to keep the evergreen foliage in good condition.

Young trees in their first two years need 25–40 litres two to three times weekly through the hot months. Use drip irrigation with emitters spread around the canopy edge rather than hose flooding at the trunk — this encourages a wider, deeper root system and cuts the evaporation that drives up a DEWA bill. Do not let an established alstonia dry out badly in summer; unlike a ghaf or casuarina, it will drop leaves and thin out if repeatedly water-stressed.

Best Mulch & Depth

A 50–70mm layer of coconut coir organic mulch over the root zone is especially valuable for a moisture-loving tree like alstonia. In UAE conditions coir cuts surface moisture loss by up to 70% versus bare sand, which keeps the root zone cool and evenly damp and lets you meet the tree's higher water needs with less irrigation — a real saving through a long hot summer.

Keep the mulch 50–100mm clear of the trunk to prevent collar rot. Coconut coir is pH-neutral (5.8–6.8), lasts 18–24 months in UAE conditions, and adds the organic matter and biological life that sandy soil lacks as it breaks down. Size your order with the mulch calculator and follow the installation guide for correct depth and clearance. Compared with bark products, coir holds moisture better on sand, as our pine bark versus organic mulch comparison explains.

Soil & Fertiliser

Alstonia tolerates the UAE's sandy, alkaline soils (pH 7.5–8.5) but does best with reasonable drainage and organic matter worked in at planting, given its preference for richer tropical conditions. It is a moderate feeder that appreciates the support of regular but balanced fertilising to sustain fast growth and dense foliage.

Apply a balanced NPK feed in October as growth resumes and again in early spring. A feed with adequate iron and micronutrients helps counter the alkaline soil's tendency to lock up trace elements. The most common problem is iron chlorosis — new leaves yellowing between green veins — which you correct with a chelated iron (Fe-EDDHA) soil drench rather than more nitrogen. Because alstonia grows fast and holds a heavy canopy, keep the decomposing coir mulch topped up so the soil biology and organic matter that support nutrient uptake keep improving year on year.

Sun & Position

Full sun to partial shade — alstonia is adaptable and will grow in a range of light, though full sun gives the densest, most symmetrical canopy. Salt tolerance is only moderate, so it suits inland and suburban gardens better than exposed beachfront plots with direct salt spray. It is reasonably wind-firm once established but young trees benefit from staking against shamal gusts.

Positioning matters more for alstonia than for most trees, for one reason: the strongly scented cool-season flowers. Keep it away from bedroom windows, majlis seating and courtyards where the heavy perfume could be unwelcome — an avenue, boundary or park-edge position is ideal. Give the vigorous roots a couple of metres of clear soil from paving, pipes and walls, and allow room for the fast-spreading canopy. The milky latex means siting it away from areas where children play and pick at bark is also sensible.

Common Problems

Strong-smelling flowers — not a disease but the most-reported issue; the cool-season blooms are intensely fragrant and can trigger headaches or complaints if the tree is near living spaces. Solve it at planting by siting away from windows and seating.

Iron chlorosis — yellow new leaves with green veins on alkaline soil; correct with chelated iron, not nitrogen.

Leaf drop and thinning — from summer water stress; alstonia is not drought-hardy and needs consistent irrigation.

Mealybugs and scale — sap-suckers on shoots and leaf whorls, with sooty mould following; treat with horticultural oil in cooler weather.

Spider mites — on dusty, stressed foliage in summer; hose down and improve watering.

Root rot — from waterlogging or poor drainage; keep mulch off the trunk and ensure the site drains. See more choices in the plant guide library.

Seasonal Care Calendar

Related Plants

Alstonia shares its plant family with the fragrant frangipani, a smaller, better-scented flowering choice near seating. For evergreen shade with fewer quirks, the neem tree is a dependable alternative, while for summer flower colour the royal poinciana and yellow copperpod pair well nearby.

Frequently Asked Questions

Why does my alstonia smell so strong?

In the cooler months alstonia produces clusters of small greenish-white flowers with a powerful, heavy fragrance — its most talked-about trait. Some people enjoy it, but many find it overwhelming, and it can trigger headaches when a tree in full bloom sits close to a bedroom window or seating area. The scent is seasonal and passes with the flowers. The real fix is placement: plant alstonia away from living spaces from the start.

How much water does an alstonia tree need?

More than a desert native. A mature tree needs roughly 70–120 litres per week in peak summer, split into two or three deep waterings, dropping to 30–50 litres every 10–14 days in winter. Young trees want 25–40 litres two to three times weekly for their first couple of summers. Alstonia is not drought-hardy — let it dry out badly in summer and it will drop leaves and thin out, so keep irrigation consistent.

Is the blackboard tree fast-growing?

Yes, notably so — speed is one of its main attractions. Alstonia establishes and puts on height quickly, delivering usable evergreen shade faster than most trees grown in the UAE, and it holds that canopy through winter rather than dropping it. Good summer water and a coir mulch layer to conserve moisture support the fast growth; just avoid over-feeding nitrogen, which produces soft, wind-vulnerable shoots.

What mulch should I use around an alstonia?

A 50–70mm layer of coconut coir organic mulch over the root zone. It is especially useful for a moisture-loving tree like alstonia because it cuts soil moisture loss by up to 70% in UAE heat, keeping the root zone cool and evenly damp so you meet the tree's higher water needs with less irrigation. Keep it 50–100mm clear of the trunk, and top up every 18–24 months as it breaks down and feeds the sand.

Is alstonia poisonous?

Like others in the Apocynaceae family (including frangipani and oleander), alstonia exudes a milky latex when cut or broken that can irritate skin and should not be ingested. It is not a tree to plant where small children pick at bark or leaves, and gardeners should wash off any sap after pruning. Handled sensibly and sited away from play areas, it is a perfectly manageable ornamental shade tree.

Why are my alstonia's new leaves turning yellow?

Almost certainly iron chlorosis, the usual nutrient problem on the UAE's alkaline soil. High pH (7.5–8.5) locks up iron, so the newest leaves yellow between their green veins. Correct it with a chelated iron drench formulated for alkaline soil (Fe-EDDHA) rather than adding nitrogen. Keeping a decomposing organic mulch layer topped up gradually improves nutrient availability and helps prevent the problem returning.

Where should I plant an alstonia in my garden?

Somewhere it can grow fast and shade freely but away from the house — an avenue, boundary or park-edge position is ideal. The key consideration is the strongly scented cool-season flowers, so keep it clear of bedroom windows, the majlis and courtyard seating. Also give its vigorous roots a couple of metres of clear soil from paving, pipes and walls, and allow room for the wide, fast-spreading canopy.

Do alstonia roots damage paving and pipes?

Alstonia has a vigorous root system — not in the notorious, structure-cracking league of conocarpus, but strong enough that it should not be planted tight against paving, walls or pipe runs. Give it a couple of metres of clear soil, water deeply to encourage roots downward rather than shallow and spreading, and it will make a sound long-term shade tree without threatening nearby hard surfaces.

Is alstonia salt tolerant enough for coastal UAE gardens?

Only moderately. Alstonia suits inland and suburban gardens better than exposed beachfront plots with direct salt spray and brackish irrigation, which can scorch its foliage. On a coastal site, plant it behind a hardier salt-tolerant windbreak such as casuarina or conocarpus, which will shelter it from spray, or choose a more salt-hardy species for the front line of exposure.

When should I plant an alstonia in the UAE?

In the cooler months from October to April, ideally October–November, so the tree establishes roots before the first 45C+ summer. Work organic matter into the planting hole, water it in well, stake the young tree against shamal winds, and lay a 50–70mm coir mulch layer to hold moisture. Being moisture-loving, alstonia handles the peak of summer poorly as a new planting, so avoid summer planting.

Should I prune my alstonia tree?

Prune for structure while young, in the cool season (October–February), to build a strong framework for the fast-spreading canopy, and remove dead, crossing or damaged limbs on established trees. Wear gloves and wash off the milky latex afterwards. Some gardeners prune to reduce or delay the heavily scented flowering near living areas, though the surest scent management remains careful siting at planting time.

Does alstonia lose its leaves in winter?

No — it is evergreen and holds its glossy, whorled foliage year-round, which is a large part of its value as a constant shade tree. It may shed and replace leaves gradually as any evergreen does, but it does not go bare in winter. Keep up modest winter watering (30–50 litres every 10–14 days) and the canopy stays dense and healthy through the cooler months while it flowers.