PLANTING AVOCADOS

PLANTING AVOCADOS COMMERCIALLY

 

Commercial Plan:  Hass Avocado

When planting an avocado orchard, three objectives to consider are:

  1. to maximize production during the early productive years of the orchard
  2. to provide for cross-pollination, and
  3. to provide for a systematic tree-removal program to maximize production at maturity.

Maximizing early production

Early production can be maximized by planting trees closer together than that which is considered ideal for the same variety at maturity. In so doing, all the land and solar energy are effectively and efficiently used. When trees are small and production is light, the production per acre is in proportion to the number of trees. Young tree population may be twice that of mature tree population, therefore production can be doubled. This situation may exist until trees start to crowd and the lower fruiting surfaces are lost due to shade.

Cross pollination

Field trials and grower observations continue to support the need for cross-pollination for avocados if maximum production is to be attained. Cross-pollination has three prerequisites;

  1. varieties of both A- and B-type flowers must be present,
  2. both varieties must bloom during the same period,
  3. either bees or other large insects must be present.

In addition, optimum day and night temperatures are required for flowers to function properly, bees to perform ade4quately, and for the fertilization and development of the resulting embryo into a young avocado fruit.

Tree removal program

If an orchard is close set at planting time to maximize early production, then as the orchard matures the grower faces a problem of excessive tree crowding with reduced fruiting surface, resulting in lower production. Crowding also increases harvest costs since the only fruit produced is high above ground in the hard-to-reach canopy of remaining foliage.

Admittedly, orchard thinning - the removal of producing trees - is one of the more distasteful tasks for any grower. A serious grower must deal with tree crowding with positive steps, and these must be taken soon enough and with conviction.

There is no set rule for timing orchard thinning. When the orchard should be thinned depends on the original spacing and the rate and type of tree growth. The rate of tree growth, in turn, depends upon the variety, soil type and depth, and climate - while the type of growth varies with each variety. Thin out trees before crowding and before the loss of sunlight causes shading out of the skirts or lower fruiting surfaces.

The decision as well as the task of removing trees in crowded orchards is made easier if an orchard is originally planted with a plan which includes all three stated objectives.

A planting plan

The following is a planting plan suggested for avocado growers in Ventura County. It may also be applied to other areas with any suitable varieties.

The Hass and Bacon are the most commonly planted varieties in Ventura County. Both complement each other in this planting plan.

The Hass is a semi-spreading tree requiring at least a 40'x 40' planting distance at maturity. It is a precocious bearer. The flower type is A.

The Bacon is a tall, upright tree requiring less ground space at maturity. It is also a precocious bearer. The flower type is B.

These two varieties complement one another as to flower type and growth habit. While Bacon fruit is of lower quality than the Hass, it does provide the necessary pollen for the Hass flowers and because of its growth habit, it can be planted between mature Hass without over-crowding.

The suggested planting distances for Hass are any combination using 18 and 22 feet as parameters. Hence, 18x18, 18x22, 20x22, etc., etc. depending on soil type and depth which affects the ultimate size of a tree. This planting plan can be used with any of the planting distances mentioned above.

A common planting distance is 20x20 feet. Remember in developing a planting plan, each group of four Hass trees, after two or three tree removals, should "see" a Bacon tree if adequate pollen is to be provided.

Original planting

At the time of the original planting (figure 1), the odd numbered rows are solid Hass. Every other even numbered row (2, 6, 10) starts with a Hass, then a Bacon, and three Hass, alternating down the row. The alternate even numbered row (4, 8, 12) starts with three Hass, then a Bacon, and alternates down the row. There are 100 trees per acre (97 Hass, 13 Bacon).

Original Planting
   
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Figure 1
 
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First removal

When the trees start to crowd, in about eight years with normal growth rate, the first tree removal should be undertaken. Figure 2 is a plot plan after the first removal of trees. Every other tree in each row (or diagonal rows) has been removed, leaving 55 trees per acre (42 Hass and 13 Bacon).

First Removal
   
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Figure 2
 
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Second removal

Normally, a second tree removal is necessary about four years after the first. Figure 3 is a plot plan after the second removal of trees. Here all trees in every fourth row (4, 8, 12, etc.) are removed to provide drive rows. Also, the remaining Hass trees in the even numbered rows (2, 6, 10, 14, etc.) are removed.

After the second removal, there are 43 trees per acre (30 Hass, 13 Bacon).

Second Removal
   
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Figure 3
 
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Final Pattern

Figure 4 is the plot plan after the second removal. Trees are 40 feet apart each way with a Bacon tree in the center of each group of four Hass trees. Every fourth row is a drive row. There are 43 trees per acre (30 Hass and 13 Bacon).

Final Planting
   
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Figure 3
 
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If conditions are such that trees start to crowd again after several years at the final planting plan (Figure 4), a number of alternatives may be used to again prevent crowding, namely:

  1. stumping by blocks,
  2. stumping by rows
  3. stumping and topworking,
  4. topworking to different varieties,
  5. thinning to hedgerows, and
  6. hedging and topping

This planting plan for Hass and Bacon, if rigidly adhered to, and if tree thinning is done at the proper time, will accomplish the original objectives of:

  1. maximizing early production,
  2. providing for pollination, and
  3. maximizing production at maturity through a systematic tree removal program.



Planting Avocados

 

It seems like the simplest thing is the hardest. Recently I was called out to evaluate why newly planted trees were failing at two sites and they both had a common problem. In one case the trees had been planted too deeply at the beginning. At another, a large amount of planting amendment had been incorporated, and over a year's time the trees had settled, so that they too had their graft unions covered with soil. In the latter case, the trees' unions were 4-8 inches below grade. It seems appropriate to review basic planting practices. In the best case scenario trees are planted from February to May, but depending on the area they can be planted at other times, as well. Gentle handling of the trees from nursery to the field and into the ground is essential, especially for clonal rootstocks.

Basic planting steps

  1. Dig a hole somewhat wider, but no deeper than the sleeve that the tree comes in. Making the hole wider (18 inches) allows room to manipulate the tree by hand and remove the sleeve once it is in the hole. Making the hole deeper than the sleeve allows for soil to accumulate around the graft union. Even if the hole is backfilled to the "appropriate" depth, because of subsidence of the loose earth, the tree can become buried. Do not put gravel in the bottom of the hole. This is commonly thought to improve drainage. It does not, it makes it worse.
  2. Gently tamp loose earth around the tree. Do not back fill with a planting mix. This creates a textural discontinuity which interferes with water movement both to and anyway from the tree. The fill soil should be free of clods to avoid air gaps and poor contact between roots and soil. Do not cover the root ball with soil; the irrigation water needs to come into direct contact with the root ball.
  3. The trees should be watered as soon as is practical after planting. Create a basin 3 feet in diameter around the tree and fill with about 5 gallons of water.
  4. Using drip irrigation the, the emitter should be attached to the trunk, so that water goes directly onto the root ball. Shrinking and swelling of the polyethylene tubing can move the emitter off the ball.
  5. Prior to winter rains, the basins around the trees should be broken down to prevent soil saturation. After about 4-6 months the drip emitters can be moved from the trunk to 6-8 inches from the tree. Moving the emitters avoids keeping the trunks wet and reduces the likelihood of crown rot.
  6. In most situations, newly planted trees should be irrigated every 5-10 days with 2-5 gallons of water for the first 2-4 months until the roots get out into the bulk soil. Depending on what the weather is like, they still might require frequent irrigations, because the rooted volume holding water is still small. After the first year in the ground, another dripper can be installed on the opposite side of the tree. As the tree grows the number of drippers should be increased or the system converted to fan or microsprinklers.

In root rot conditions

Planting in ground that has had root rot can add some new steps to the planting process. On relatively flat ground (<15 degree slope) trees will benefit from being planted on a berm or mound. This creates better aeration and drainage for the roots. It also means that the trees tend to dry out faster, so more frequent irrigation may be necessary. Where machinery can be employed, creating berms is usually less expensive. Surrounding soil should scraped to the planting site, and little incorporated with the soil surface where the berm or mound is to be built. In bringing surrounding native soil to the planting site, it is important that an interface between the imported soil and the soil surface is not created that alters water flow through the mound into the bulk soil. The berms can be built 1.5 to 2 feet high with a 4:1 slope. The raised planting position should be irrigated to settle the soil. The soil should then be allowed to dry out prior to planting to avoid mucky soil. Only clonal rootstocks should be replanted into root rot soil. Applying gypsum (15 pounds per tree), a thick layer of mulch around the base of the tree (3-6 inches deep, but not immediately on the stem of the tree) and finally application of fungicides will help. Application on the berm or mound also protects the soil from eroding away with rains.

The key to root rot has always been dependent on irrigation management. There is nothing more important than getting the right amount on at the right time. If you are doing interplanting into an existing orchard where trees have died, it is imperative that the new trees be put on their separate irrigation line so that they can be irrigated according to their needs. Simply putting a smaller emitter on the young trees compared to the older trees means that they will still be irrigated on a cycle that is not optimum for their survival. It doesn't matter if you are using clonals; they will die just as easily with poor water management as a seedling.