Water the tree right after planting: 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. If the roots are bound (roots are tangled, matted and growing in circles), score the sides of the ball with a knife.

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.

Planting
Do not dig the planting hole any deeper than the roots of the tree as purchased. The hole may be made somewhat wider than the root mass. The hole can be slightly wider than the root ball, or fork-loosened laterally beyond what is needed for the width of the root system.

In most soils, no planting mix is needed. Just backfill with native soil, making sure there are no clods that will cause air pockets around the roots. Consider nutritional amendments that can become part of the backfill at this time. Place NO conventional (commercial) fertilizer in direct contact with roots. Certain organic and naturally occurring materials may be considered with caution. Mulches, compost or organic matter will best serve trees when applied to the surface around trees after planting rather than blending with the backfill.

Make a small cone of soil in the center of the hole and place the tree so that the roots are fanned out around the cone. Add soil until roots are covered by several inches and tamp gently, then add the same amount of phosphate as was placed in the bottom of the hole. Cover with soil to fill the hole using the soil which was removed to make the hole. It is not necessary to add soil amendments. Do not use fertilizer containing any nitrogen when planting.

Plant the tree a little high to allow for tree settling in the hole. The darker color or stain on the trunk below the bud union usually indicates the original soil level. Orient the inside of the trunk bend (the concave bend immediately above the bud union) toward the north or northeast to reduce heat stress and sunburn to the trunk curvature above the union; the sun is less able to impinge directly on the young bark and trunk when so oriented. Using the best, friable, clod-free soil available at the site, backfill leaving no air pockets around the root system. After settling, the soil level next to the trunk should be at or below the level at which the tree grew in the nursery field.

After planting, the soil line on the trunk should be a couple of inches higher than the surrounding ground line, which in turn, should slope downward away from the tree to prevent water from accumulating near the trunk. The graft union should be four to six inches above the soil surface.

A basin for water may be made around the base of the tree (not next to the trunk). Fill the basin with water several times to settle the soil around the roots and to remove any air pockets.

After planting, irrigate once if necessary, keeping in mind that young trees will not be extracting or depleting soil moisture until growth is well underway (several inches of new growth).

Watering

Do not allow the ball to dry out. Once your tree has begun to establish a root system, keep the soil damp but not soggy. Water deeply. Apply water according to the needs of the tree or as your soil dries out. Check the soil in the root ball for moisture by probing with a finger to assure yourself that the plant needs water.

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.

Fertilization

After trees have made six to eight inches of new growth, three applications over the growing months may be used of one of the following:

This amount should be placed six inches to three feet out from trunk and watered in immediately and thoroughly.

Insect Control
Do not spray young trees for pests that attack the crop until after they start bearing fruit.

See this link for pest management:

http://www.ipm.ucdavis.edu/PMG/selectnewpest.citrus.html

Vertebrate Pests
Young fruit trees are especially liable to severe damage from gophers, rabbits, voles (mice) and deer.

Rodents Pocket gophers eat roots, bulbs and entire young plants. Eradication by trapping is the most efficient method. Two types of traps are commonly used: box traps and Macabee traps. Poison baits are effective, but can cause harm to dogs and cats if eaten.

Moles are only present in good soils as they are primarily insect eaters (especially earthworms and larvae). A spear or harpoon trap is usually used for control.

Ground Squirrels (Gray Diggers) gnaw roots and bark and will climb trees for fruits and nuts. Controls are baited box-type traps placed near burrows, anticoagulant poison-bait placed inside burrows, and gas bombs placed in the burrow. Metal guards around tree trunks will prevent them from climbing up into trees.

Birds  The only sure solution to bird depredation is to use screening or netting material. This must be tied about the tree trunk to be effective in keeping the birds out. The use of owl statues, flexible snakes and cat statues will only be effective in gardens if they are repositioned every few days.

Deer They will spend more time looking for food in gardens as wild plants dry out, and will eat foliage and fruit of nearly anything that grows. The only fool-proof protection against their depredation is fencing. On level ground a seven foot woven-wire fence will usually suffice. An “outrigger” extension on top makes it harder to jump. Individual wire cages around plants and cylinders of wire around trees may be effective also. Repellents can work if renewed frequently, especially after each rain, watering or several days of exposure.

Weeds

If you want good growth, it is imperative that weeds are not allowed to develop near your trees. Keep the space clean for a full six feet from the base of your tree. Allow no weeds or grass to grow in this area and apply no systemic weed killers that may be absorbed by the tree roots. Mulching (keeping it away from the trunk) can be very effective at controlling weeds.