Germination temperature
Warm conditions; sow in the hot season or when seedbeds stay warm.
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Jerusalem thorn is a thorny, extremely drought-tolerant small tree with green bark and fragrant yellow flowers. Its hard seed responds best to sandpaper nicking or a long soak, and it is a serious invasive weed in some countries, so check local rules before planting.
Warm conditions; sow in the hot season or when seedbeds stay warm.
Shallow: cover the seed with a thin layer of sand or fine soil.
2-10 days for treated seed; most scarified seed is up within 3 days.
Not needed for germination; seedlings need full sun.
Nick the seed coat with sandpaper, or soak in water for 2-4 days.
Both; it grows easily from seed in a nursery or sown in place.
Jerusalem thorn seed is oblong and hard, about 11,000-15,000 seeds per kg. Not every seed in a batch is hard: in a Brazilian trial about 60% of untreated seeds still emerged, but much more slowly than treated seed.
Recommended. Rubbing the side of each seed on sandpaper until the coat is thinned (on the side opposite the scar) gave 99% emergence in a Brazilian trial and 70% in an Iranian one, against about 15-60% for untreated seed. Nursery workers sometimes use a short dip in concentrated sulphuric acid; 5 minutes worked in trials, but longer exposure damaged seed. Acid is not a home method; sandpaper or nail clippers do the same job safely.
Not needed. The seed has a hard coat, not a cold requirement.
A long cold soak is a good home alternative to nicking. ICRAF lists soaking seed in water for 3-4 days, or scarifying and then soaking in warm water for 1 day. In an Iranian study, leaching seed in running water for 48 hours gave the best result (75%), ahead of sandpaper (70%) and hot water at 90 °C (194 °F) for 15 minutes (57.5%). Change still water daily. A brief 1-minute hot-water dip gave low emergence in the Brazilian trial.
Sow in warm weather. In the wild, seeds germinate after several days of prolonged rain in the warm season.
Keep it shallow, just covering the seed with sand or fine soil; treated seed in the Brazilian trial emerged well from the surface of moist sand.
A free-draining sandy mix. The tree grows on desert gravels, sands and saline soils, so rich compost is not needed.
Keep the mix moist until seedlings emerge, then water less often. Avoid soggy trays.
Not required to germinate, but move seedlings into full sun at once; shade slows growth.
ICRAF gives 2-10 days with 30-70% or more germination. In the Brazilian trial, 80% of scarified seed had produced normal seedlings by day 3, against about 40% of untreated seed.
Move seedlings into deep pots or polybags while small, and plant out in full sun before the taproot gets long. Handle with gloves once the thorns form.
Young plants respond well to fertiliser and can grow up to 1 m (3 ft) a year. Protect them from termites and from waterlogging in the first months.
Cause: part of every batch has a fully hard coat. Fix: nick each seed with sandpaper or soak for 2-4 days, and sow again any seeds that have not swollen.
Cause: stale water during a multi-day soak. Fix: change the water daily, or use the sandpaper method instead.
Cause: termites damage young plants; wet, heavy soil also weakens them. Fix: use a sandy mix, avoid overwatering and keep the nursery free of woody debris.
Cause: snow scale can attack the tree. Fix: scrub off small infestations and keep the tree growing strongly in full sun.
In Australia Jerusalem thorn is a Weed of National Significance, declared in every state and territory, with at least 800,000 hectares infested. It can escape cultivation elsewhere too. Before planting, check local rules and never plant it near rivers, wetlands, dams or floodplains.
A typical mature plant produces about 5,000 seeds a year and the pods float, so water carries them long distances. Collect and destroy fallen pods if you do not want seedlings, and keep machinery and soil from infested areas clean.
It is extremely drought resistant, survives dry seasons of up to 9 months by dropping its leaflets, and grows with 200-1,000 mm of annual rain from sea level to about 1,300 m (4,300 ft). It tolerates saline soil and drastic pruning, making it useful in hot, arid regions.
The seed is orthodox: kept airtight at room temperature it stays viable for about 3 years.
Nick or soak the seed before sowing, and plant Jerusalem thorn only where it is permitted.
Rub each seed on sandpaper until the dark coat is thinned on one side, or soak the seed for 2-4 days in water changed daily. Both outperformed untreated seed in published trials; acid is not needed.
It can be. It is a Weed of National Significance in Australia and spreads easily along waterways. Check your local regulations and avoid planting it near water or natural areas.
Quickly once the coat is broken: 2-10 days in warm conditions, with most scarified seed up within about 3 days.