A member of the Cashew and Sumac (Anacardiaceae) family, the Pistacia genus has 12 species, of which
Pistachio, grown for its edible seed, is the most well known.
Lifespan: Several hundred productive years.
Leaf retention: Deciduous.
Growth rate: Slow.
Mature Size: 20-30' high and as wide for the male tree,
but in cultivation they seldom attain that height. Female trees are usually smaller.
Flowers: Clustered, tiny, brownish-green, separate
male and female flowers on separate trees. The flowers have no petals, do not produce nectar,
and the females do not attract pollinating insects.
Pistachio trees are planted in a ratio of one male upwind for every 5 to 8 females, or in some
cases, a male tree branch is grafted onto a female tree.
Bloom: Late spring. Male flowers may bloom before female
and some farmers will store the pollen and manually pollinate the female later.
Pistachio trees are alternate bearing, with female trees producing fruit heavily every other
year, and using the process of bud dropping in alternate years to achieve this. Pruning in
heavy years is the best way to reduce, but not eliminate, alternate bearing.
Self-fruitful: No. Wind blows pollen from male to female
Years before fruiting: 5-8 years. Full production may
not be attained until 15 or 20 years.
Fruit: A green, thin-fleshed mesocarp covers a thin
hard shell (the endocarp) enclosing a seed called the pistachio nut. When the seed is fully ripe,
the mesocarp turns red and wrinkled and starts to separate from the shell, which usually splits open.
Seeds vary from yellow to green inside, with green being the most prized. Some shells will be
blank, lacking seeds. Blanking occurs most often in "off" years when the tree bears little or
no fruit. Maintaining proper irrigation and boron levels reduces blanking. It is desirable for
shells to split and failure to do so can be caused by drought stress. Normal splitting rates
Months for fruit to ripen: 4-5. The seeds are harvested
by shaking or pounding the tree, collecting the fallen seeds, and removing the mesocarp with a
squeeze between thumb and finger.
Storage after harvest: Frozen seeds last for months
before processing. Otherwise, the seeds must be hulled and dried within 24 hours after harvest
to avoid aflatoxin infection.
Leaves: Green leaflets, oval with a tip on the end, in
sets of five leaflets.
Stems: No thorns.
Roots: The species Pistacia integerrima is often used
as a rootstock. It is vigorous, resistant to fungal diseases and nematodes, and produces extensive,
deeply penetrating roots. That species and its hybrid are named Pioneer Gold and Pioneer Gold II.
Cultivars of Note:
'Peters' Male tree, heavy pollen producer, blooms before
and during 'Kerman'.
'Kerman' Female tree, bearing heavily but in alternate
years, producing above average size seeds. Late blooming.
Wildlife: The seeds attract birds and squirrels.
Toxic / Danger: Pistachio trees are not poisonous to
humans or pets but are toxic to horses.
Origin: Desert regions from Syria to Afghanistan and
possibly India. Pistachios have been cultivated for over 9000 years.
Cultivation and Uses
USDA hardiness zones: 8-10. Pistachio trees need a long,
hot, dry summer and a moderately cold winter. The standard rootstock should not be exposed to
temperatures below 10°F. Summer humidity results in extensive fungal disease and poor
Chill hours: 900 to achieve 50% bloom.
Heat tolerant: Yes.
Sun: Full sun.
Drought tolerant: Yes.
Water after becoming established: Deeply, once a month
in winter. Deep water once every 7-10 days in spring and summer until harvest is over.
Soil: Very well draining, deep, dry, sandy loam with a high
calcium carbonate content, pH 7.0-7.8 (neutral to slightly alkaline). This tree is very tolerant of
salinity and boron.
Fertilize: Use composted manure once in early spring.
Mulch: Organic mulch reduces evaporation loss and reduces
bud drop in heavy crop years.
Spacing: Trees are often planted 11 to 30' apart.
Planting: This tree is not suitable for a container after
the first three years and should be in the ground.
Prune: Blooms are produced on one year old wood. Any winter
pruning may significantly lower seed production.
Litter: Leaves in fall, flower buds, fruit if not harvested.
Propagation: Grafted cuttings.
Pests: This tree is prone to root rot in poorly draining soil.
It is prone to Verticillium wilt in soils where other plants have exhibited that disease, and
prone to other fungal and bacterial diseases in poor growing conditions.
Uses: Edible seeds. Male trees can produce resin used in
lacquers and varnishes.
This is a desert tree that expects a dry climate, but with some underground water,
and a prolonged, moderately cold winter.
The seeds contain a high quality oil but the seed itself is more valuable.
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