Planting
The avocado is a shallow rooted tree (most of the feeder roots are in the top 6 inches of soil) that needs good aeration. It does well if mulched with a coarse yard mulch, which means one that is woody and in 2-inch pieces, Redwood bark will work and maybe cocoa bean husks and shredded tree bark. Coarse yard mulch is available at some garden supply centers. Be sure it is COARSE, not fine, yard mulch and disease-free to prevent introducing diseases to the tree (such as root rot).
The current recommendation is to mulch with approximately 1/3 cubic yard per tree when planting. When applying the mulch, be sure to keep it about 6-8 inches away from the trunk of the tree. Avocado trees like the soil pH to be around 6 to 6.5. If possible, plant the tree in a spot protected from wind and frost. Also, avocado trees typically do not do well planted in lawns.
When to plant
Avocado trees like warm ground. Ideally, plant them between March and June. If planted during the summer, they may become sun-damaged because they can't take up water very well when young.
How to plant, step by step
- Select a site that has full sun.
- Dig a hole twice the width of the avocado tree's root ball and the same depth as the root ball. Measure by shovel handle.
- If the tree has an open-bottom sleeve, ease the tree into the hole rather than dropping it in.
- If the tree comes in a pot with a bottom, remove the tree carefully from the pot, cutting the sleeve not too deeply, and set the tree into the hole slightly above the level of the surrounding soil.
- Support the root ball bottom with your hand to prevent breaking the ball and losing roots. The avocado root system is very sensitive and needs great care to avoid disturbing the root system when transplanting.
- If the tree is root bound, however, loosen the soil around the edges and clip the roots that are going in circles.
- Fill the hole partially with soil while the sleeve is in place temporarily to support the root ball.
- Backfill the soil into the hole. Don't add gravel, mulch, or soil amendments to the backfill to avoid excess salinity, ammonia gas, and water movement problems. The sooner the roots get out into the surrounding soil, the better the tree will do.
- Complete the fill by tamping the soil to eliminate air pockets. When re-planting in root-rot infested soil, add gypsum around the base of the young tree at the rate of 10-20 lbs. per tree. Add mulch on top to complete the planting process.
If the soil is heavy clay, elevate the tree on a mound (berm) to improve drainage. Make the mound 1to 2 feet high and 3 to 5 feet around. Spread 20 pounds of gypsum around the base of the tree and mulch the area with 6 inches of woody mulch keeping the material about 6-8 inches away from the tree trunk.
Watering
When watering the tree, it is best to soak the soil well, then allow it to dry out somewhat before watering again. Of course, like most plants, you don't want the tree to get too dry.
The rule of thumb for mature trees is about 20 gallons of water a day during the irrigation season. Seedlings will require quite a bit less.
At planting, avocado trees can hold about 2 gallons of water. Depending on the weather, they might use 1gallon of water a day along the coast. Typically, water the trees 2-3 times a week. As the roots reach out into the bulk soil, you can apply more water. By the end of the first year, diminish watering to about 1 time per week.
Check the soil before watering, to make sure it has dried somewhat. If the soil from around the roots can still hold the impression of your hand when squeezed, it still has enough water.
Fertilizing
The major nutrients that the avocado tree needs are nitrogen, phosphorous, potassium (N-P-K on the fertilizer package label), and zinc (Zn). For young avocado trees, the recommendation is 1/2 to 1 pound of actual nitrogen per tree per year. Spread it out over several applications as long as it totals 1/2 to 1 pound of nitrogen. The other important nutrient for avocado trees is zinc. A general-use home fertilizer that is used for houseplants normally should work. Feed some zinc once a year if the fertilizer does not have zinc. Read the package label to be sure.
Mulching
Avocado trees greatly benefit from mulches. Any organic material can be used, including the fallen leaf litter from the avocado trees. It is best not to rake the fallen leaves. They provide free mulch for the avocado roots, which are close to the surface. A thick layer of mulch can suppress some soil pathogens, including Phytophthora cinnamomic fungus, which causes root rot.
