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Citrus and Avocado Tree Planting

Garden & Landscape

A fully-leaved, sub-tropical evergreen must be treated differently than the standard, deciduous, temperate plant. Normally, it is planted somewhat later in the year so as to capitalize on the warming spring soil, and special allowance must be made for the plant's high transpiration rate.

Avocados with clonal rootstocks do not have a central taproot, so their earthen balls may not be as physically stable as those of non-clonal, seedling-stocked tree. Therefore:

(a) Never lift or carry them by grasping the trunk or stake, and
(b) Be sure the tree is lowered into, and correctly set in the planting hole before you slit the poly container.

Water the tree right after planting: The planting of avocado trees is different from deciduous trees. Your new tree has a large number of active, working leaves which must be kept well supplied with water at all times so as to function and not wilt. Since the ball of the tree contains all of the tree roots it must be kept moist to serve as reservoir for the water. When you remove the plastic sleeve from the ball, you will find that many of the roots are concentrated at the outside vertical surface. It is, therefore, very important that the tree be watered immediately after planting, since these surface roots will otherwise be unable to function properly.

Leave the upper surface of the ball exposed: The soil in the ball has been specially formulated -- it contains special nutrients and is designed so the ball will readily absorb water that is added directly to its upper surface.

Specific Planting Steps

1. Dig a hole much wider than the ball of your tree. An 18" auger makes an ideal hole. If your soil is good you need not add any soil amendment to the hole. Avoid adding more than 5% (by volume) organic manure to the soil.

2. Adjust the depth of the hole so that the upper surface of the tree ball will be just even with the surrounding ground when the tree is lowered into it.

3. Lower the tree into the hole, slice the container open vertically on one side, and backfill with 6" to 8" of loose soil.

4. Pull the plastic tube out of the hole and away from the tree and discard it. This will leave the roots exposed on the surface of the ball.

5. Gently tamp the loose soil around the ball immediately. Promptly fill the rest of the hole with loose soil, gently tamping as you fill. Fill it up to the top, but leave the upper surface of the original ball exposed.

It is important that the loose soil you put back in the hole be free of large clods, as these do not dissolve easily with water and will cause air spaces which are injurious.

The upper surface of the ball is left exposed so that you may add water directly to the ball, even after the tree is planted. If you cover this surface with anything, do not let it be soil; use sand, loose sawdust, coarse gravel, or anything through which water will pass very rapidly.

6. Build a basin with a three foot diameter around the tree, sloping the bottom of it so that all water drains to the exposed surface of the ball. The basin should have a capacity of about five gallons.

7. Fill the basin with water once. If it drains rapidly, fill again. If it requires two minutes or more to drain, do not refill.

8. Reform the bottom of the basin, as the dirt in the hole should now have settled somewhat. Be sure that the top of the ball is still exposed.

It is a good idea, once the basin has stabilized, to cover the bottom with straw, sawdust or some other mulching medium.

9. If you plan to use drip irrigation, be sure that the emitter is fastened to the exposed ball of the tree with a "U" shaped piece of wire or hook. Check your emitters frequently to see that each tree is getting watered; clogged emitters are a common problem.

10. Once your tree becomes established and the roots start reaching out into the surrounding soil (usually about 1 to 2 months after planting), the emitter should be moved away from the top of the ball to a distance of about 6" to 8".

11. As the roots extend further outward and downward, you will want to add more emitters and move them further away from the trunk of the tree. A fully mature avocado (six years old) will often have four to five emitters spaced in a ring around the tree near the drip line.

12. Under normal circumstances, water the young tree every 5 to 10 days for a period of 6 to 10 weeks. Two to five gallons of water per irrigation will be sufficient provided the ball itself receives water each time and remains damp inside. Do not allow the soil to remain soggy; a happy medium is mandatory.

If you plan to plant these trees in areas where root rot has occurred, or if the area has become secondarily contaminated with Phytophthora cinnamomi, chemical control of this pathogen is recommended to assist the establishment of the trees. Ridomil® and Aliette® are suitable systemic fungicides registered for use on avocados.

Watering

Do not allow the ball - ever - to dry out. Avocados are native to areas which, unlike California, have almost daily rains during the summer. Their favored soils under these conditions are often acid, sandy and weak, characterized by good internal drainage which doesn't allow them to remain soggy. Therefore, once your tree has begun to establish a root system, keep the soil damp but not soggy. Water deeply. We recommend the use of a soil core probe, slanted toward the side of the ball so that it penetrates the ball about 12" below the soil surface, in order to determine soil moisture. Apply water according to the needs of the tree.

The tree may be watered by basin for a full year. However, the basin should be broken down during the wet season if water has any tendency to stand in it. After a year you should consider the use of sprinklers or drippers.

Warning: Avocado roots are very easily suffocated by excessive water. This problem is most severe between planting and the period when the roots reach out into the surrounding soil. This means that the trees are particularly vulnerable when planted in the fall. Therefore, under no circumstances allow water from rains or other sources to stand around the tree ball or run over the ball for extended periods of time. Such treatment will almost certainly result in rotting roots, and probably, in an unsatisfactory tree. If the tree is planted on a slope you may consider placing a diverting trough above the tree in such a way as to deflect any water currents away from it.

Mounding: In heavier soils it has been shown to be helpful to plant the trees on 12" to 18" mounds sloping to 5' to 8' bases. This allows optimum aeration for the root and assures the proper planting height.

Fertilization

During the first two or three years, your tree should be fairly heavily fertilized so as to make maximum early growth. Heavy fertilizer to one person often means entirely something else to another, so we suggest that the following rates be used during the pre-bearing years:

Formulation to be applied per 1,000 gallons of irrigation water.

2 lbs. of dry ammonium nitrate or 1/3 gallon of ammonium nitrate solution 20-0-0

1 lb. dry potassium nitrate

1 pint 75% food grade phosphoric acid

NOTE: Dosages are given on the basis of the quantity of water applied to the tree. The most effective way to apply the fertilizer is probably by proportional and continuous addition of the fertilizer to the irrigation water. Since this is frequently impossible, the next best thing may be to add it during alternate irrigations. Be sure to double the amount per application in such a case. Remember to be careful not to apply all of the fertilizer in one batch while irrigating, but find some manner in which to spread out the application during a large part of the full irrigation cycle.

If you are unable to add the fertilizer to the water, or estimate the correct amount from the foregoing, you may sprinkle a tablespoon of nitrogen-bearing salt (ammonium nitrate, urea or such) over the root area and water it in thoroughly. Repeat every three or four weeks. Take care not to concentrate it in one area. Increase the dosage gradually according to the increasing size of your tree. Apply the plant food around the drip line, or in the path of irrigation water.

A fully bearing orchard is usually fertilized at the rate of 1 to 1 1/2 lbs. of actual nitrogen for an average sized avocado tree (one that has a foliage diameter of about 20 feet). This can be taken care of by sprinkling 1 to 1 1/2 lbs. of dry ammonium nitrate on the ground around and beneath the skirts of the tree two or three times a year. Wash the fertilizer into the ground with a good soaking (2 inches of water). Early spring, summer and fall are good times for fertilizer application, as the avocado roots will be active then. We suggest, as a special precaution, if you have only one or two trees, that you add also, a half pound of Ciba-Geigy 138 iron chelate and a zinc chelate to the soil at the same time that you are adding the nitrogen. The chelates will correct many cases of leaf yellowing.

Frost Protection

Young avocado trees are very vulnerable to prolonged frost conditions. However, there are certain precautions you may follow during the first year or so which will often save a tree.

Wrap the trunk of your new tree with heavy paper, corn stalks or the special thermal wraps. If this is done to a point above the bud union, the chances are that you will have a complete budded tree when winter is over even though the exposed parts of your tree are killed.

At the onset of spring, you will be able to unwrap the damaged tree and select a shoot or shoots, above the bud union, so as to renew your tree. Do not remove dead tree parts until new shoots are growing well.

An even more effective insulation to preserve the bud union is a collar filled with sawdust to a point 6 to 12 inches above the union. The collar may be 5 or 6 inches in diameter. It is almost impossible to freeze tissue within this mass of sawdust.

Foliage is more difficult to save under severe frost conditions. Any wrapping around and through it will help. Sometimes bunches of straw are intertwined with the foliage and matted around the branches to serve as an insulating mass. A suspended canvas and wood canopy above the tree will help. Under very extreme conditions, people have erected tents and placed lighted electric bulbs within the structure. Remember two things:

1. A complete enclosed covering of polyethylene or other non-breathing plastic is often worse than nothing -- especially where it touches the tree.

2. Trees do not survive well in darkness, so the tree must be allowed to see sunlight during the day.

All in all, we recommend the thermal wraps mentioned first above or the sawdust filled-collar.