Prior to the planting operation and fall rains, it may be advisable to strip spray the area to be occupied by the young trees with a pre-emergent herbicide such as PrincepR. This chemical can lie on the surface of the ground for up to six weeks without degrading and will be washed into the surface when rains do come. A contact weed killer such as weed oil or ParaquatR can be used together with the PrincepR, as these are quite compatible in the same mix. This mix will kill the weeds currently growing in the strip and prevent weed growth during the fall, winter, and spring, thus giving the young tree a chance to become established without weed competition. Weed control progressively becomes less of a problem as the trees become larger and shade out the weed growth.
The preferred planting dates for avocados begin about 15 February with the last tree planted no later than 1 May to permit the maximum benefit of the growing season, yet allow the trees to harden off before the following winter. Although the cooler nights of the fall season will cause a cessation of growth, no fertilizer should be applied to trees after Labor Day in areas where there is a reasonable expectation of frost by mid-December. Though mature leaves may withstand the frost, the tender, succulent growth of new leaves can be severely damaged.
With trees grown in planting tubes or containers, ,which in all probability have been tip grafted, the tube is placed in the hole to a depth where the top of the soil in the container is level with, or slightly above, the ground surface. While the tube is in the hole, the plastic is removed by slitting the tube lengthwise with a linoleum or other sharp knife. Do not attempt to slit the tube, remove the plastic, and then lower the tube of dirt and roots into the hole. Too often the dirt crumbles, leaving a bare root tree in your hand. This tree will take a long time to grow if it does not die. After the plastic is removed the soil is backfilled around the mass of dirt containing the roots. The topsoil should be filled in first to provide good soil for the roots to establish themselves in, and the subsoil added last. Tamp the soil firmly around the mass of dirt as it is filled in and water the tree as soon as practicable to wet the soil and drive out any remaining air pockets.
Field budded trees are very seldom offered for sale any more, but in the event one does purchase budded trees, it is best to plant the tree with the cut surface facing in a northerly direction. After the bud takes, the seedling rootstock is severed just above the bud union and the cut surface painted black with a nontoxic asphalt emulsion compound such as “Tree Heal” or “Tree Seal.” It is this black surface that should point north to avoid sun damage.
Even though the soil is packed tightlyand the surface of the tree ball level with the surrounding soil, there may be some water runoff with sprinkler irrigation, which can be reduced by mulching.
This writer would prefer not to use basins around young trees because basins tend to collect cold air and rain water during the winter months even when “V” notches are cut in the basins in the fall of the year permitting the cold air and water to escape. However, with a sprinkler system, there can be water savings for the first few months of tree growth if you place an old can over the sprinkler and allowing a basin to be created by the blockage the can creates. With drip irrigation there is no need for basins because the water delivery is so slow that there is little or no runoff.
A tree wrap should be tied around the young tree trunk to protect it. Sun can damage the green wood, as can the cold. Modest protection from small rodents is also provided by the wrap.
Growers seem to prefer a wrap of corrugated cardboard, the exterior of which is coated with thin aluminum for maximum protection and to reflect heat. Old magazines or newspapers also work quite well, especially on a few back yard trees. Remove all plant growth below the top of the wrap and tie the top and bottom somewhere between loose and snug. The wrap should be positioned to cover the bud union. If cold is apt to be a problem, you may want to mound up some soil or straw mulch outside of the wrap but over the bud union for added cold protection.
With the young tree firmly set in the soil and wrapped, the next step is to loosely tie the tree to the 2”x2”x6’ stake above the tree wrap using any one of the plastic materials that are available commercially. Tying and retying the tree to the stake should be a continuing process until the time the diameter of the area at the bud union exceeds the size of the stake. The stakes should be of good quality, because after two to four years they can be removed and made into l”x2”x6’ stakes useful for supporting future scaffold branches. You can easily make the narrower stakes by passing them through a circular saw. Adjustable tree hooks, available commercially, are placed over the end of the stake with the branches in need of support placed on the hooks.
Sometimes it is necessary to replant trees among older trees in an orchard. Nurserymen usually supply larger size nursery trees for that purpose. These replant trees may receive less fertilizer than those planted earlier unless there is an injector in the irrigation system. If not, it might be advantageous to place a tablet or granular slow release fertilizer in the tree hole outside the ball of the tree about halfway down its length, thus insuring a constant source of nitrogen for the young tree.
In the permeable and thin soils often found in California’s avocado growing areas, using mulching materials is a must to preserve surface moisture and to improve the tilth of the soil. Baled straw is apt to be the cheapest mulch when the cost of labor and material are significant. If the price is right, pine chips and shavings are good. Well-composted manures make a fine mulch and help to provide humus, but involve much labor. In addition, the source should be known to be free of root rot fungus. When estimating the mulching needs of new trees, counting seven young trees to the bale may be about right. However, it will be necessary to repeat the mulching after the previous mulch has decomposed, because mulches break down rapidly under a heavy fertilization and irrigation regime. Mulching becomes unnecessary when trees are big enough to provide their own leaf mulch.
REFERENCE CITED
What on Earth is Soil? Cooperative Extension, Univ. of Calif., AXT-n161.