Grove of date trees.

Dates

Phoenix dactylifera

Origin:

Iraq, but records of its culture go back to 4000 BC and its widespread human distribution and selection since then to north Africa and the Middle East has contributed to some controversy.  There are 13 species in the genus, all native to the tropics or sub-tropical areas of Africa or southern Asia.  P. dactilifera is thought to have been derived from two other species in the genus.  Essentially, the whole genome has now been sequenced (>96% of genes).

Climate:

It is adapted to very hot and dry climates, with ideal temperatures of 21-27°C but withstanding up to 60°C.  It is tolerant of some frosts, and in the fruit maturation period needs long hot, dry and low humidity summers with root access to generous soil moisture conditions.  Most are grown within latitudes of 15-35°N.

Plant Description:

This monocotyledonous long-lived dioecious species has an erect trunk, 40-50cm in diameter and up to 30m high, with 1 or more off-shoot suckers at the base.  There is no taproot. Instead fibrous roots may extend laterally and in depth for several metres; most however are within 2m of the trunk.  The crown has 60-150 long-lived (7 years) glaucous pinnate leaves, 3-6m long, with narrow pinnae tapering to a sharp point at the tip.  Basal leaflets are modified into spines. 

Relatives:

Arecaceae Family, which includes coconut, peach palm, oil palm, betel nut and salak. Some, such as the Canary Island palm (P. canariensis) are used as ornamentals, and their fruits are used as feed for livestock and poultry.

Soils:

They can grow on a wide variety of soils, from sands to clay, but yield is increased if they have good water retention without waterlogging.  Salinity tolerance is believed to be the highest of all tree crops and mature plants can survive with total dissolved salts >2% and minimal effect on yield; young plants are more sensitive. 

Propagation:

The most common approach is to use the 3-5 year-old off-shoots arising at the base of young plants.  Best results are obtained with the larger ones and with some leaf pruning to minimise excision and transplant shock.  Seeds and tissue culture are also sometimes used.  Seedlings do not come true to type, only half will be productive females and these will inevitably have lower yields.

Cultivars:

There are thousands of confusingly-named cultivars but 75% of world production is produced by the top dozen.  Barhi, Deglet Noor, Halawy, Khadrawy, Medjool, Thoory and Zahidi, are just a few of these, and all have special characteristics.  Females are selected for the quality of their fruit, time of maturity, rain tolerance and suitability to the local climate, while males are selected for time of flowering and the number of flowers.

Flowering and Pollination:

Inflorescences are enclosed in a spathe in the early stages of development.  In spring, individual yellowish-green flowers on female trees occur on spiral rachillae, usually in threes, on a flat tapering peduncle, 100cm long, which initially is upright and later drooping  The 50cm long rachillae on male trees is upright. Normally only one ovule of the 3 carpels per flower is fertilized, but some fruit may develop parthenocarpically.  One male tree produces sufficient pollen for 40-50 females.   Pollination, normally in spring, may be effective from 7 days before spathe opening to 10 days after.  Wind is the main pollinating agent but insect pollination is also possible.  Commercially, artificial pollination is frequently used where pollen is collected and then used at appropriate times, or bunches of male flowers are cut and tied in amongst flowering females.  There are incompatibilities between some male and female cvs resulting in poor fruit set; rain and low temperatures (<21°C) also reduce fruit set.

Cultivation:

Off-shoots should be planted in full sun.  Soil moisture is essential when they’re young and during fruit maturation when older.  If this is not addressed during hot dry periods then trees will be stunted and unproductive.  Mature producing trees in California are given 220-300kL/tree/yr, which increases to 15-25kL/tree/mth in peak summer.  Fertilization results in better yields, although this may only be seen after some years.

Wind Tolerance:

Like most palms, good.

Pruning:

Trees are not self-pruning so dead and dying leaves should be removed, usually after fruit harvest.  Basal spines on living leaves are also removed to reduce injury. Some living leaves may be removed but at the risk of reducing yield; a ratio of 8-10 leaves/bunch is targeted.  Fruit thinning may also be practiced, decreasing the risk of an alternate bearing habit developing.

The Fruit:

Variable in size and shape, depending on variety, climate and management.  Generally 4-7 x 2-3cm weighing around 60g.  There are 4 ripening stages given unfamiliar Arabic names – Kimri (immature green), Khalal (mature full-coloured), Rutab (soft brown) and Tamar (hard raisin-like) with sugar content rising progressively to 70-90% dried matter. Such dates also have good fibre, Ca, Mg and vitamin A.  The single seed is 20-30 x 5-8mm.  Different cvs have a range of flavours and textures. 

Fruit Production and Harvesting:

Plants can begin fruiting in 4-6 years with full production in 15-20.  Economic life is 40-50 years but trees may live for 150.  Rain during the ripening period can cause fruit splitting.  Harvesting is in summer, the period depending on the intended use.  In Australia, most of the dates you will encounter will be pitted and in the later Rutab and Tamar stages of maturity with better storage properties than the earlier two. Climbing the tall trees is necessary for picking.  Average yield is 40kg of fruit/tree/year, increasing to 100kg with intensive management.

The fruit is gathered before it is quite ripe, and dried in the sun to make it keep, as fresh dates soon ferment and cannot be kept for any length of time. Yellow types and the red elongated variety of date are eaten fresh or are frozen immediately after harvest. Freezing improves quality and this is true for many other fruits with astringency.

Fruit Uses:

Dried dates are eaten as is, or their high sugar content can be exploited in many processed foods, eg chutneys, jams and breads, where they provide a sweetening effect but have the advantage of adding more nutrients than pure sugars.

Pests and Diseases:

Dates can be afflicted with many pests and diseases worldwide, but these are very dependent on site, cv and management.  Possible pests in WA could include scale, birds and rodents; weeds should also be controlled.  Any diseases will likely be due to fungi or phytoplasmas; no viral or viroid infections have so far been reported. Wasps can be pests as they seek sugar.

Comments:

Producing your own dates requires significant effort and determination - they need leaf pruning every year, the spines can cause injury, they are dioecious, pollination has to be managed, they need generous water supply and harvesting requires getting to the top of tall trees.  They will fruit in south west WA but cvs adapted to cooler climates are needed.  Countering this, the fruit can be obtained cheaply in retail outlets.  Their high sugar content also needs to be recognised re diet.

Many attempts to establish dates in Australia have been made. An early research station in Carnarvon had some, and a commercial date farm of 700 trees exists near Alice Springs, The Desert Fruit Company, and another new farm, Tamara Plantation.