CHAPTER II
GROVE DEVELOPMENT
As we view new plantings of avocado, we find at least two
types of grove ownership: (a) investment for speculation, often under limited
partnerships, where some partners may never see the land or the grove and, (b)
small ownership, where the owner plans to retire a few years down the road. The
owner sees the raising of avocados as a way of life and may dream of going out
into his grove at night just to listen to the trees grow. It is to the latter
owner that the following is addressed.
Before entering the avocado industry, one should examine the
economic trends of the industry -- especially before land acquisition takes
place. Pamphlet material is readily available on this subject and on many other
facets of the avocado industry through the Farm Advisor’s office in the various
counties or through the Cooperative Extension, University of California,
Berkeley, California 94720.
Also, there are many fine orchard development companies that
would be happy to review the industry for the prospective grower. In San Diego
County, the farm advisor has made himself available through office days, ranch
calls, newsletters, and avocado schools for the dissemination of useful
information to the neophyte as well as the seasoned grower.
CLIMATE
Climate is probably the most important factor involved in
growing avocados. There may be ample water and the best soil, but without
suitable weather conditions the avocado will not grow. It is rather demanding
in its requirements of heat and cold and does not tolerate extremes of either.
Coastal areas, with their relatively small diurnal temperature range, provide
the tree with just what it wants. As we move progressively further inland,
conditions become less inviting for tree growth. Temperature fluctuations are
greater, winds may be damaging, and water losses greater due to these factors.
In short, avocados will not grow and produce successfully in desert areas where
it is too hot or in low-lying areas that get too cold.
Cold air drains down slopes the same as water does and comes
to rest in the lowest point, after which time it accumulates, and as the cold
layer gets deeper, it slowly progresses up the slope. The point where
equilibrium is reached between the dense, cold air at the bottom and the warmer
air from above is usually the frost line. Avocados will grow above this frost
line, but below this line they will be subject to occasional freezes and will
not produce crops on a regular basis, though the tree may survive. When
choosing a site, it is necessary to have a slope long enough that the air will
continue to drain away below the trees and thus pull warmer air from above to
offer frost protection. The further inland one goes, the higher the altitude
must be to provide adequate air drainage. The ideal grove site in northern San
Diego County would be situated at about 750 to 1500 feet in elevation with good
air drainage on all sides. The most favorable exposure would be to the south or
the west to avoid the damaging Santa Ana winds that can literally blow the
fruit off the trees and sometimes blow the trees over as well.
No matter how carefully we may select a piece of land by
looking at its physical features, there is no substitute for placing
thermometers on the piece in question to give an accurate indication of its
frost, or lack of frost, potential. To do this one should have several minimum
registering thermometers placed in areas where the cold is most apt to settle,
part way up the slope and at or near the top. The thermometer must be protected
from the direct rays of the sun by a box-like cover, usually made of wood. It
is mounted on this frame with a screw through the hole on the left and a small
screw or nail on the right. This screw is placed where the right end of the
thermometer will rest on it at an angle slightly higher than horizontal. To
reset the thermometer, the right end is removed from the nail and lowered until
the black marker falls to the ambient temperature at the time of the reading.
Thermometers should be read and reset no less than once a week and a record
made of the low point reached during the week by each thermometer at its
location. These records may later be compared with a known area where records
are kept to determine how much warmer or colder your spot is. To get an even
more accurate picture, a thermograph can be used to register the duration of
the cold. Thermographs are quite expensive, whereas the low cost minimum
thermometers would provide accurate enough information for grove selection.
It is important to remember that the avocado is native to
tropical regions and that it is being grown in southern California under
conditions that are marginal at best. In our arid to semiarid climate we must,
as nearly as possible, try to provide the missing elements found in the
tropics. By doing so, we can make the tree feel more at home and coerce it into
producing crops for us.
WATER
An adequate water source must be provided for the avocado,
which will not produce in our arid to semi-arid climate without it. The source
can be a well or wells located on the property and developed by the owner at
his or her own expense. If the property is located within a water district, the
district line should (although it may not always) run to the edge of the
property with a water meter owned by the district. It is up to the property
owner to run distribution lines from the meter to water his trees. The water
should be delivered to the meter in adequate amounts and pressures and be of
suitable quality. There should be no more than 700 parts per million (ppm) of
total dissolved solids in the water.
SOIL
Soil is formed from the underlying rock by weathering, which
may include wind, rain, heating and cooling of the rock, stream abrasion, and
in northern areas, freezing, thawing, and glacier action. As the roots of
plants decay, chemical action takes place to dissolve the mineral particles and
the roots themselves break apart rocks and hard soils into ever-smaller pieces.
Soils may occur in a wide variety of colors from black to white and everything
in between. They may form in place (residual soils) or may be transported from
their place of origin by wind or water (depositional soils) (Fig. 1).
Soil is composed of three sizes of particles: sand (the
largest), intermediate silt, and clay (the finest). The capacity of the soil to
hold water and air is dependent on the particle size. Sandy soils have a low
water holding capacity but good aeration, and clay soils hold water well but
are poorly aerated. Soils with a high humus content have a more nearly uniform
water capacity and aeration, regardless of the particle size (Fig. 3).
It should be noted that the accumulation of well-decomposed
organic matter typically found in the upper horizons of soil (humus) contains
many nutrients known to satisfy the needs of plants. Avocados enjoy an
environment high in decaying matter in the root zone; for adult trees, mulch
from fallen leaves is often sufficient, but for younger trees, growers may need
to add mulch.
The percolation of water through a humus soil permits plant
roots to extract moisture and nutrients more efficiently, and humus tends to
act as a reservoir of soil moisture for the benefit of the plant. The
percolation affect is usually referred to as water infiltration. A well-drained
soil would have a high rate of infiltration.
Avocados will grow in many soil types, but for best growth
and production the soil should be medium textured to provide good aeration.
Avocados have a shallow root system, but there should be at least 3 to 4 feet
of soil over a preferred granite base. In San Diego County, such suitable soils
are classified as Cieneba, Fallbrook sandy loam, Vista sandy loam, and
Escondido fine sandy loam with preference given to Vista sandy loam (see Table
1). Growers can easily observe the profile and depth of the soil where there
are road cuts, because roads will most often bisect the areas to be planted.
The previously
mentioned soil types will generally have a near neutral pH between 6.5 and 7.5,
which is optimum for best avocado growth and production. pH is a chemist’s
symbol that expresses the degree of acidity or alkalinity of a substance on a
scale of 1 to 14, with 1 being most acid and 14 most alkaline. Neutral is 7.
Each number is 10 times more alkaline than the one below it or 10 times more
acidic than the number above it.
In summary, the three essential growing conditions for
avocados are:
1. Relatively frost-free land;
2. A well-drained soil with a near neutral pH; and
3. Adequate water of suitable quality.
When the economic questions have been resolved, the location
of suitable lands is the next order of business. This is probably best
accomplished through the employment of a real estate broker and consultation
with specialists from the Soil Conservation Service, U.S.D.A., who can offer
expert knowledge on the suitability of lands (Fig. 4).
Since the advent of drip irrigation and the higher cost of
land, growers have been planting on steeper slopes than they formerly had.
Regardless of the slope, provision must be made for working the ranch and for
the removal of fruit. There are some clear advantages to a higher elevation and
steeper slopes because they are apt to be warmer and have soils that drain
well. Therefore, steep slopes should not be viewed with dismay, though without
careful planning of roads and access, maintenance and harvesting could present
major problems. It should be kept in mind that many ranches are successfully
managed on less than perfect lands, but may require more of everything in the
grove manager’s bag of tricks.
Poor quality
Figure 4. Soil Conservationist Sam Aslan holding his
soil-coring tool “John Paul”.
LAND PREPARATION
Land Clearing By
Machine
Brush removal by machine is usually performed on gentle
slopes by using a bulldozer blade, discing, or mowing with a heavy-duty mower.
Many growers want the land ripped 18” to 36” deep to break up the old gopher
runs, allow better water penetration, and bring to the surface any rocks or
roots that should be removed. Ripping also permits growers to see what is
underneath the surface, such as clay pockets that need to be identified.
Avocados do not like “wet feet” and clay, with its slow drainage,
would surely create an unsatisfactory condition for tree growth. After ripping,
the land should be floated (smoothed). This produces a polished land
preparation job that will permit easier future maintenance of the grove.
If the slope is too steep or too rocky for clearing with
mechanized equipment, native brush can
be cut to ground level with hand tools such as machetes, axes, saws, and brush
hooks. Hand clearing tends to be more costly than machine brushing and has the
inherent difficulty that the brush may regrow and have to be removed again
later, increasing future grove care costs. On the other hand, the remaining
roots will stabilize the soil for erosion control. In the past, brush that was
removed was placed in windrows and burned, but because fire burns very rapidly
in the windrow, it may burn out of control and damage adjacent property.
Burning is much easier to control and less likely to cause damage if the brush
is placed in a series of separate piles that can be burned one at a time.
Sometimes brush is piled in ravines and permitted to decompose. This practice
invites an infestation of rats, squirrels, and poisonous snakes by providing
protected home sites for them.
Runoff occurs when storm or irrigation water exceed the
soil’s capacity to absorb them. This can be responsible for severe erosion and
grove damage (Fig. 5).
Erosion control on newly opened land should be carefully
considered because winter rains can be very destructive. Common practice and
prudence dictate that all buried main lines and submain lines be carefully
covered with straw to reduce erosion damage. Likewise, swales, barrancas, and
other potential trouble areas should have a similar straw treatment for the
same reason.
Poor quality
Figure 5: This newly planted grove has been ravaged by a
deep ravine from an unexpected summer rainstorm. Erosion control must be
considered even during the dry months. However, all is not lost since the
ravine may now be used as a bed for drainage pipe to carry away future
floodwaters and irrigation runoff.
Some steep hillsides may require straw for the entire
cleared area at the rate of 2 tons per acre. Straw is suggested because it is
apt to be relatively inexpensive and is an easier material to use (Fig. 6).
This writer remembers vividly the damage done on his
neighbor’s land on two successive wet winters in spite of the good preventive
measures taken to reduce the problem. The key word in the use of erosion
control materials is “liberal,” because our crystal balls for determining
weather do not usually work well. If the erosion control measures are taken
late in the year, it may be desirable to sow barley before strawing, as well as
in unstrawed hazard areas. This work should be done by hand. If the acreage is
large enough, it may be more economical to sow the seed by aircraft. Ideally,
the winter rains will germinate the seed, providing the desired growth for
protection.
Poor quality
Figure 6: This young grove is well mulched with plenty of
straw to prevent erosion. Despite a 2˝” rain storm in August 1977, the ground
remains unscarred by erosion. This grove is off to a good start. As the straw
decomposes around the young trees, it should be replaced to maintain mulch.
It is in this stage of development that the long range
detail planning takes place. Decisions made now will affect the ranch for years
to come; therefore, it is important to anticipate future needs. Some of these
considerations are noted as follows.
There may be problem areas necessitating the drainage of
floodwaters from rain and sprinkler tail waters. There are contractors who
specialize in this work, and planning for it in the early stages of development
is often beneficial to growers. Most growers prefer the type of control that
has an underground drain line, usually of concrete tile placed in a barranca,
with control dams and drop inlets spaced strategically the length of the drain
line.
A swale, or marshy low-lying area rank with vegetation, is
occasionally found in avocado growing areas. A swale is gentle in slope,
contrasted to steeper canyons, and is likely to be filled in during the land
preparation phase. These areas should not be planted with avocado unless
suitable drain lines are installed to make the land usable. A marshy area, also
called a loblolly, is often an indication of a nearby spring and the soil may
remain waterlogged year-round without sufficient root aeration. In wet years,
flood waters may remain in the area and kill the trees when their roots do not
get the oxygen they need and simply rot away.
Bees are important in the pollination of the avocado and
ideally should be located in the interior of the grove. Like humans, bees are
lazy. Avocado blossoms are the last choice for a bee because it would rather be
out in the citrus or native brush seeking a lighter kind of nectar. If bees
have to go through the avocados to reach the flowers they do like, they do a
better job of pollinating the avocado trees.
Beekeepers like to have an all-weather road to the hives’
location to accommodate their large trucks (Fig. 7). These locations should
have sufficient space for the bee boxes to be worked on both sides of the
truck. For your future crop, you will need the apiarist more than he will need
you, so it would be wise to provide a situation to his liking. Beehive
locations should be at least 700 feet away from a dwelling to satisfy the
members of the household as well as the bee inspector.
Poor quality
Figure 7. Beehives should be located on an all-weather road
to provide access for the beekeeper to manage the hives.
If you plan to build a home on the property, provisions will
have to be made for the home site and its associated septic leach field. A
consultation with an architect or builder would be in order at this point.
Fruit Removal Systems
If land is steep, give some thought to the picking and
removal of fruit from the grove. Regrettably, at this writing, solutions to
this problem have not crystallized in the industry. There have been tests
utilizing helicopters, mules, and burros, and all leave something to be
desired. However, an avocado harvesting committee has been active in seeking an
answer to this vexing question and we await further reports from them.
The following suggestions are mentioned for possible
consideration and incorporation into the ranch plan.
B. W. “Bud” Lee, Ventura county farm advisor, has introduced
to us an interesting idea practiced in the Japanese citrus industry that may
have merit. The Japanese have been using a permanently installed monorail
system with a gear rack on the under-side of the rail to which the pinion gear
of the motor unit is engaged. The rails are of galvanized steel measuring about
2” square, upon which the power units are mounted in such a way that the car
can be detached and moved to another rail elsewhere in the orchard for further
movement of fruit.
The engine itself is a 3 to 4 hp., air-cooled, two cycle
type common in the U.S. The rails are tailored to fit the terrain by bending
the rails to fit at the site and can match very steep lands. On 55% slopes, the
monorail can carry 330 to 440 lbs. moving at 55 feet per minute. Trailers,
usually measuring 2’x 6’, are added to carry the fruit.
Kicker-arms are mounted on the rail supports so that that
the motor unit can be stopped at any predetermined point by striking the clutch
handle on the unit, thus disengaging the power. The systems are reported to be
remarkably stable and operate without swaying, wobbling, or falling off the
rail. Costs for these systems in the U.S. are still being studied.
On steeper slopes, footpaths running horizontally between
the tree rows have been useful for fruit removal and other cultural care
activities. Such paths can be hand dug or formed by a special Japanese machine
designed for that purpose.
Some growers have found it advantageous to terrace their
steep slopes by machine and plant on the outside edge of the terrace. This
method permits grove work to be performed more easily than on footpaths.
Two young engineers in the Escondido Area, Chuck Cawley and
Vic Roberts, recognized the fruit removal problem of steep slopes and have
advanced a canvas chute system. Picked fruit is funneled into a chute that
moves the fruit down the slope and into the waiting bins without bruising the
fruit. The chute provides a direct route for fruit from the picker’s bag to a
fruit bin or field box at the bottom of the slope. This system permits the
relocation of the chute and its supporting frames from one point to another
within the grove. Anchors on the high and low ends of the setup are the only
permanent part of the installation. It is the belief of the writer that this
system will offer the most efficient service at the most economical price of any
of the arrangements now on the horizon, but the future may bring us better
systems.
In the mid 1970s Dick Markano of Fallbrook began developing
and marketing the “Agri-Tube” as a modern method of hillside harvesting. It is
said to be a cost effective way to remove picked fruit from slopes above 20°
(36%) by increased worker productivity.
The Agri-Tube operates as an inflated zigzag tube that
guides picked fruit, by gravity, from the picker’s bag to the bin in an
undamaged condition.
The Agri-Tube is stored on a reel, mounted on a small
trailer that can be towed to an uphill location. Because of its lightweight and
lack of frame or anchors, it can easily be rolled down the slope to a ranch
road and bin. A small gas-powered compressor fills and maintains air pressure
in the tube until it is ready to be rolled up on the reel and moved to another
location.
A word of caution when picking thin-skinned varieties such
as Fuerte, Bacon, Zutano, and Covocado: the fruit should be dry -- no fog or
light mist. When these classes of fruit are damp, they pick up a burned or
“toasted” appearance from handling and motion in the picking bag that may tend
to downgrade them.
All orchard operations require practical and usable work
areas. Growers will need underground fuel storage, fertilizer storage, bins and
field boxes, and parking areas for vehicles along with covered areas for
mechanical repairs and servicing. Buildings used for storage should have locks,
as theft can be a problem in unsupervised areas. The use of helicopters for
orchard spraying is becoming more common and a helicopter landing pad big
enough for the helicopter and its attendant servicing equipment may be
necessary.
When land has been cleared so that it is possible to see
what the terrain is like, an experienced tractor operator will be able to cut
in the ranch roads to fit the terrain. Aside from roads to a home site and to
bee spaces, ranch roads will take on more importance to the working ranch as
the years roll on. Three tree rows between ranch roads should be a minimum. The
actual number of rows between roads will depend on the steepness of the
terrain, with more roads on the steeper slopes. Growers generally feel that
there should be no more than six tree rows between ranch roads, and that a
perimeter road is necessary as well (it can act as a fire break). Fire is
always a threat to an avocado orchard. Because there is apt to be much fuel in
an orchard, it would be prudent to clear barrancas of brush for additional fire
protection. Perhaps negotiations with neighbors for a firebreak on their
undeveloped lands would be advantageous.
Ranch roads can become washed out where they cross drainage
channels. Runoff from natural rainfall and from irrigation water should be
channeled through culverts under the road and into catchment basins to prevent
erosion. If possible, the culvert should extend well past the edge of the road
before the water begins its fall to a lower elevation.
Steve White, a grove
manager in (city), has been doing something interesting in his own grove by
planting what he calls a citrus barrier along the outside edges of his ranch
roads. The theory behind this practice is that citrus roots seem to repel the
avocado root rot fungus and thus bring a measure of control should infection
ever get started in the grove. Bearss lime on macrophylla rootstock seems to
perform well as a barrier and also provides a good crop of limes.
Other amenities include access roads or a public or private
roadto the property, because fruit will have to be hauled out someday. While
electrical service may not be essential to the performance of the grove, it is
certainly useful for wind machines, pumps, irrigation timing devices and
housing for the owner and workers.
If the owner intends to live on his or her ranch, some
consideration may also be given to the proximity of schools, churches,
recreational areas and shopping centers. Telephone service, good radio and
television reception, and fire and police protection are important to the city
dweller, but are also important to the farmerin an ever-greater degree.
Strictly speaking, these aspects have nothing to do with whether you have a
successful avocado grove, but they will certainly make living in the country
more pleasurable and add to the quality of life.
