Pistachios

• There is a vegetative flush April to May right after flowering
• Each axillary bud contains the entire shoot with leaves and new axillary buds and terminal buds
• They bloom on one year old wood
• If there is a large crop one year, there will not be a lot of axillary buds for the next year
• If there is a large crop the year before then most differentiating buds on the new growth will abscise
• The developing crop will cause the abscision of the axillary buds that could have been next years crop
• Terminal buds form in June
• The steps to bud growth are: 1-3 terminal buds develop in June, in July of the next year differentiation occurs, then there is a rest, in October pistillate initiation occurs, then there is a rest, and finally in March 2 years later inflorescence develops and the flowers bloom
• There could be a second vegetative flush in the summer
• If there is a second vegetative flush then it will help young trees with filling out the canopy but in old trees the growth will only occur at the top and be pruned out during the dormant season
• If there is a secondary vegetative flush depends on the rootstock
• The juvenility period is very long, the first crop is not harvested until 7 years old and the trees are not in full production until about 10-12 years
• Fruit development occurs in 3 stages
• During the first stage of fruit development cell division is occuring and the shell and hull are growing rapidly (no kernel)
• The first stage of fruit development happens in mid April to mid May
• During the second stage of fruit development, there is no growth. This is happening mid May to late June and you can drought stress
• During the thrid stage of fruit development, the kernel is filling which causes the shell to split. This occurs from July to August
• Only about 4-10% of flowers set fruit and 5-30% of these are blanks
• Pistachio trees are dioecious
• The female and male flowers are on two separate trees
• Female flowers form on an inflorescence called a Rakus
• There are 100-200 flowers per rakus
• The flowers are wind pollinated and do not have petals or nectaries
• Maturity moves from one end of the tree to the other so all the flowers do not open at the same time
• Flowering occurs early to mid April
• The flowers and vegetative growth are expanding at the same time
• Female flowers form on one year old growth
• The main female cultivar is Kerman
• The dominate male cultivar is Peters and it blooms early to mid April
• The male flowers form inflorescences on one year old wood
• There is usually one male tree per 24 females
• Every 5th tree in every 5th row tends to be male
• The chill requirements between the male and female cultivars are very different
• The orchards are set on relatively wide spacing and a square design
• You need a minimum of 20ft of distance between rows for equipment
• 20 x 18 is the minimum spacing if you want to run a hedger in the orchard
• The trees are not planted on high brims or high density so that you can still cross hedge
• Button emitters are used so that cross hedging can occur across rows
• Cross hedging is used to increase light penetration
• You should not go longer than 1/4 mile without access to the road so that you can turn around equipment