Avocado

About Avocado

The avocado is an evergreen tree that can reach 30-60 ft tall (NC State), so porch growers need a grafted dwarf such as 'Wurtz' (sold as 'Little Cado'), which stays about 10 ft. Mexican-type avocados handle the most cold, and grafted trees start bearing in about 3-4 years. A tree grown from a grocery-store pit makes a nice houseplant but rarely fruits in a pot.

NC State lists zones 9-12. Cold tolerance depends on type: Mexican-type trees can take the low 20s F, Guatemalan types about 24-28 F and West Indian types only about 25-30 F (UF/IFAS); UC Ventura puts damage at 25 F for 'Bacon' and 'Zutano', 28 F for 'Fuerte' and 29 F for 'Hass'.

When to plant

Timing is counted from your average last spring frost (and first fall frost). Sow & Tell works out the actual dates for your ZIP code.

No source ties the move outdoors to a frost date; set a potted tree out after frost danger is past. In the ground, UC Master Gardeners suggest planting March through June, 23-30 ft or more from buildings and other trees (UF/IFAS). Grafted trees bear in about 3-4 years (UF/IFAS; UC Ventura); seedlings take far longer.

Soil

Loose, very well-drained soil; avocados won't tolerate flooding or poor drainage and suffer when soil pH is above 7 (UF/IFAS; UC Ventura).

Test pH first: avocados are very sensitive to pH above 7 and do best around 6-6.5; plant in loose, fast-draining soil or mix (UC Ventura; UC Master Gardeners, Contra Costa).

Feeding

• First year, every 1-2 months while the tree is growing: balanced fertilizer with magnesium, 6-10% nitrogen, phosphate and potash plus 4-6% magnesium. UF/IFAS starts in-ground trees at 1/4 lb and works up to 1 lb per application; UC Ventura instead gives about 1 oz of actual nitrogen per tree for the whole first year, split into 4-5 feedings. Use much less in a pot and follow the label.
• Each later year, spring through summer: the same fertilizer; add potassium once the tree starts bearing (about year 3). UC Ventura doubles the nitrogen each year for the first 5 years; UF/IFAS moves mature trees to 3-4 feedings a year and adds 3-4 sprays of copper, zinc, manganese and boron a year for the first 4-5 years.
• Potted tree indoors for winter: no fertilizer. Hold fertilizer until new growth appears in late winter or early spring (University of Maryland).

Don't overwater or let a pot sit in water: root rot is the main avocado killer (UC Ventura; NC State). Keep mulch at least 6 inches from the trunk (UC Ventura).

Harvest

Avocados don't ripen on the tree. When fruit reaches full size for its variety, pick one large fruit and leave it on the counter: a mature fruit softens in 3-8 days (UF/IFAS). Harvest season depends on the variety.

Avocados give one crop a year, maturing anywhere from June to March in Florida depending on the variety, and the fruit need not all be picked at once. Some varieties bear heavily only every other year; good care reduces that swing.

Varieties (20)

Pests to watch for

Scale insects, Twospotted spider mite, Thrips, Roof rats and Norway rats

Diseases and problems

Phytophthora root rot, Scab, Cercospora spot, Anthracnose, Laurel wilt, Potassium deficiency

In the kitchen

The fruit is eaten fresh once it softens after picking (UF/IFAS); Mexican types are the richest in oil and West Indian types the lowest (NC State).

Keeping it: Ripen picked avocados in a paper bag at room temperature (2-5 days), then refrigerate ripe ones for 3-4 days. Sprinkle cut halves with lemon or lime juice and use within a day or two.

Safety: People with a latex allergy may react to avocado; MedlinePlus lists it among the foods most strongly linked to latex allergy. The ASPCA names persin as the toxic compound (listed for horses).

Pets: Toxic to horses (ASPCA): persin can cause breathing trouble, heart failure and swelling