How do citrus types vary in their heat requirements and hardiness?
●The younger the plant, the more cold sensitive
●Directly correlated to the vigor and density of the canopy
●Relative ranking of citrus heat tolerance
○Grapefruit and pomelo (most heat tolerant)
○Lemon
○Sour orange
○Sweet orange and lime
○Mandarin (least heat tolerant)
●Heat tolerance and methods of heat protection
○Irrigate liberally at least twice a week during the hot summer months of June,
July, and August
○Fertilize trees during May and again during August
○Do not prune citrus trees, and allow the leaf canopies to extend low to the ground
○Paint exposed trunks with a dilute formulation of white latex paint and water
■Protect the branches and trunk from sun scald
■55% paint
■50% water
What are the most cold tolerant types of citrus?
●Kumquats and mandarins (tangerines)
●Tolerant to the low 20 to 22 degrees Fahrenheit
Which are the most sensitive to cold temperatures?
●Lemons and limes
●Tolerant to 27 to 29 degrees Fahrenheit
●Grapefruit, tangelos, and oranges are intermediately tolerant of the cold (23 to 25 degrees
Fahrenheit)
First frost date in Maricopa
●November 21st in Buckeye to December 12th in Phoenix
Average frost date in Maricopa
●February 7th in Central Phoenix to April 3 in Mesa
Cold tolerance and methods of cold protection
Study Guide 10 - Citrus and Dates
●Wrap trunks of young trees with insulating cloth to protect the graft or bud union
●Bank soil around the lower trunks of young trees to insulate the graft or bud union from
the cold
●Cover the entirety of the young trees during the nighttime hours with a thermal blanket
●Make sure young and mature trees are not nutrient stressed and are well watered before
cold nights
Be able to define the following terms:
Grapefruit is citrus x paradisi
Budding
●The insertion and enclosure of a single vegetative “bud chip” from one plant into an
opening cut with a knife in the bark of another plant to propagate a desired change of
variety or appearance
●Genetic compatibility of the bud ship with the parent plant
Rootstock
●A rootstock is a plant with a healthy, established root system, that has another plant
grafted or budded onto it
●Once graft or bud union is established, the majority of the shoot portion of the rootstock
plant is removed
●2 common rootstocks are used in the Desert Southwest
○Citrus aurantium or Sour Orange
○Citrus Volkameriana or the Volk Miur lemon
Scion
●A detached shoot or twig containing buds from a woody plant that are grafted onto a
rootstock
●Grapefruit tree example
●Graft incompatibility
○Usually graft is more vigorous than scion
Sucker
●Vigorous shoot that grows rapidly from the lower portion of a mature tree or shrub
What is the difference in size between a dwarf and standard size tree? How are dwarf trees
produced?
●Standard Citrus Trees
○Usually grow about 28 to 25 feet tall when planted into good soil with no root
restrictions and are well watered
○The mature size of standard trees is achieved after 10 to 15 years because citrus
are not fast growers
●Semi - Dwarf Trees
○Usually grow about 2/3 size of standard trees
○About 10 to 18 feet in height
○Reach full size with unrestricted root system
●Dwarf trees
○Grafted into dwarfing rootstock and reach a mature height of 4 to 8 feet
