Growing Avocados

Name confusion in the trade
Many of the varieties that have become available to the nursery trade are "found" varieties. Some of the mother trees were found in South Texas, many in and near the San Antonio area.  Growers often attach their own names to found varieties for the purposes of marketing.  Therefore, we have ended up with more than one name for the same fruit.  This is only important if you are trying to create a collection of different avocados for your table and want to avoid duplication.

• Brazos Belle is genetically identical as Wilma
• Lila is genetically identical to Opal; Opal was originally named "Opal Holland" or just "Holland"
• Fantastic is genetically identical to Pryor
• Arizona is also known as Aravaipa
• Don Juan is dual labeled as Aravaipa, but I do not think it is the same as Aravaipa at this time

Can I grow my own from seed?
Most of us have grown an avocado from seed in the kitchen window at one time or another. They make a pretty little houseplant, but don’t count on them for production. They are not a variety that is suited to our climate, they may not “come true” from seed, and they may take 10 – 15 years to fruit, it they fruit at all. When you purchase a grafted avocado, you are assured that you have a producing variety. They will generally begin bearing within two years of planting, less if you purchase a more mature specimen.

Tree selection and home nursery care - don't rush to plant that young avocado!!
I have formed an opinion over the years that avocado trees should NOT be planted in the ground until the trunk has started to form true bark.  This might be several years from the time you buy the tree.

You will notice that almost all avocado trees that are available in 3-gallon and 5-gallon pots still have immature, green trunks.  The tissue can easily be pierced by a thumbnail.  These specimens are still in their juvenile stage. During their youth, they are:

• Frost tender
• Easily sunburned
• Highly susceptible to a group of soil borne root rots

My recommendation is to buy the largest, most mature tree you can afford. If the tree you can afford still has green bark at the bottom 12” of trunk do not plant it in the ground. Plant it into a pot that is at least two sizes larger or 4” wider than the nursery pot.  Use a peat-free, compost-based potting soil that has expanded shale for aeration, drainage, and moisture control.  Step the tree up in container size each year until it has developed true bark on the bottom 12"-18" of the trunk, when it can safely be planted in the ground.

Take good care of the tree while it is in its “nursery” stage.  Fertilize and water as you would if it was planted out. It will produce light crops during this time and you can feel free to allow the fruit to develop and be harvested. It will also develop a strong root system.  Protect it from freezes in the winter and sunburn in the summer.

Once your tree has hardened off, you can plant it out with a higher success rate than setting out that tender, young, green-trunked tree. You will not lose anything by taking this precaution, and you will have less chance of losing your tree to its number one threat - root rot.  During this "nursery" stage, you can make some decisions about the permanent location of the tree, and can start your bed preparation.

Site Selection – Sun, shelter, drainage
Site location is one of the keys to success with avocados.  Their needs change somewhat as they mature.  Choose the site to suit the needs of the mature tree.  You can modify the site to suit its juvenile needs. Your site should have:

• Six to eight hours of sun - you will need to choose a sunny location.  Six to eight hours of full sun is the minimum acceptable; more is better.
• Shelter from cold north winds - if you can, locate the tree on the south or southeast side of a structure.  A sunny side yard is a good location.
• No less than 8' – 10' from structures - the tree will grow 15’ – 20’ in diameter when it is mature.  If you intend to plant more than one avocado, place them at least 15’ – 20’ apart.
• Excellent drainage - avocados will not tolerate “wet feet”.  Plan on a raised bed or a mounded area.  Both drainage zones must be met - surface drainage, where water drains from surface and does not collect around tree and internal drainage, where water percolates downward and does not leave “waterlogged” soil in or near the root zone of the tree.
• Low salinity - avocados are very sensitive to salts.  If your sol has high salinity, or is in an area that has been subjected to brackish or salt-water storm surge, you will have to take steps to remediate the salts before you can plant an avocado.

Bed Preparation
You should prepare the bed for your avocado tree as far ahead as you can.  It would not be unreasonable to prepare the bed at least a year ahead of planting.  At the very least, it should be prepared at least 6 weeks in advance.  The reasons for this will become clear in the rest of this article.

Avocados have special needs.  The bed preparation in our Garden Basics section is not sufficient for avocados.  It is not a matter of nutrition.  It is the cultivation of the Soil Food Web that is particular to avocado health and survival.

• Mark out an area at least 6’ in diameter.
• Clear the area of turf and weeds.
• Add 3” of fungal compost over the area (approx 7 cu ft).
• Add 2" of expanded shale over the area (approx 4 cu ft).
• Apply 1# or 2# of gypsum over the area.
• Broadcast a rock mineral blend over the area.
• Using a spading fork (not a tiller!), mix this very well into the top 6” - 9” of native soil.  (Do not add fertilizers at this time.)
• Top off with a good quality bed mix until the bed is raised 8” – 12” deep above the grade. (approx 19 - 28 cu ft)
• Mulch the entire area with fallen tree leaves.  The mulch depth should be at least 8".

Each of these components has a specific purpose.  Together, they support a healthy Soil Food Web for avocados.  Fungal compost will add organic matter and mycorrhizal fungi and will inoculate the area with beneficial microbes.  Expanded shale will assist with drainage, aeration, and moisture management, as well as provide a protective habitat for microbes.  Gypsum will bind up salts in the soil.  In addition, a study by the California Avocado Society revealed that gypsum used in conjunction with organic mulches has a suppressive affect on root rot pathogens.  Rock minerals are a good way to remineralize soils.  Minerals are often depleted in soils.

Topping off with bed mix is a step that requires some contemplation.  Use the best quality bed mix you can afford.  It should contain a minimum of 1/3 compost by volume.  Arbor Gate Soil Complete is an excellent choice.  Other options would be Rose Soil or Nature's Way Resources Vegetable Bed Mix.  Since you will need close to a yard of material, purchasing this in bulk will be the most economical approach.

Putting root exudates to work
If you have prepared the bed a year, or at least a season, ahead of time, you do not have to leave it fallow while you wait to plant your avocado.  Sweet Basil (Ocimum basilicum) roots secrete rosmarinic acid (RA) when they are in the presence of three major root rot pathogens.  RA  inhibits the spore germination of these pathogens, reducing their presence in the soil.  Keep the future avocado bed planted in Sweet Basil, which will grow from April through frost.  Your soil will benefit from it, and you will enjoy pesto and salads as well.

Planting
Planting should be delayed until the middle of March to avoid any chance of damage from a late frost. Container grown trees can be planted throughout the spring and early summer, but any later may not give the tree the chance to build a good system before winter.

When you are ready to plant, dig a hole that is 1-1/2 to 2 times wider than the container and the same depth as the root ball. The sides of the hole should be a shallow bowl-shape, not straight. Think “wok” not “stew pot”.

Set the tree in the center of the hole and check to make sure the graft is above soil level.  Backfill with soil until the hole is ½ filled. Lightly tamp the soil, but do not pack tightly. Fill the hole with water and allow it to drain completely. This helps settle the soil and collapse any air pockets. Finish backfilling and water in again. You may add your favorite root stimulator to the water for either or both waterings.

Note: There are several sources that recommend planting the tree in a depression where the graft is above the soil line at planting, but several inches below the grade of the bed. Over a period of 2 – 3 years this depression is slowly filled with prepared soil so the graft will eventually be several inches below grade. I do not recommend this planting method.

After your tree is planted, you will need to pay extra attention to it for at least the first two years.

Mulch
After your avocado tree is planted, maintain a 2" - 3" layer of native mulch over the entire 6' circle, keeping the mulch pulled back 2" from the trunk.  You can use a "collar" of pine straw right around the trunk, then native mulch or a combination of native mulch and tree leaves.

Sunburn protection
Young avocados are susceptible to sunburn.  If it is severe enough, it can kill the young tree.  There are several ways to prevent this:

• Erect a burlap lean-to on the south-west side for the first and second summers to protect from sun scald.
• White wash the trunk.  Use latex paint and water mixed 50:50.  Apply over the exposed trunk and branches.
• Spray with kaolin clay.  Kaolin clay is available in a wettable powder (Surround WP).  It can be painted on the trunk and sprayed on the leaves as a sunscreen.

Water
Avocados need consistent water – slowly, deeply, thoroughly – but do not allow water to stand at any time. Depending on the weather, newly planted trees may need to be watered several times the first week after planting, but never let water pool. Reduce this to one or two times a week for the next few weeks. Your goal is to provide sufficient water to establish new root development, but never to have soggy soil. After the first month, water only when the top inch of soil is dry for the first year. Do not allow the tree to become drought stressed in first few years. As winter approaches, monitor the weather before you water. Your goal is to balance winter rains with winter dry spells and drying winds.

Fertilizing
Do not feed until strong new growth appears during the second year of growth. Avocados can be fed with a slow release organic fertilizer or with a specialized avocado-citrus food. Spread fertilizer evenly around trunk out to the drip line. Compost and organic mulch can decrease fertilizer needs over time. Burned leaf tips indicate over-fertilizing. If this occurs, drench with clear water to leach out fertilizer and reduce your applications.

Established trees will benefit from an application of cottonseed meal in February. Use 9-cups per tree, spread evenly around the drip line before refreshing the mulch. You will normally feed your trees every 6 weeks from February through August, but skip the February feeding if you have applied cottonseed meal. Do not apply nitrogen rich fertilizers after August. Tender fall growth may be damaged by early frost. Kelp meal applied in September boosts cold tolerance going into winter.

Pruning
Pruning is not necessary for fruit production. Training is preferable to pruning. Training means shaping the tree in its first three years in the form you would like it to take. Go lightly with avocados. They don’t need much. Always remove and dead, diseased, or damaged wood. Remove lower branches to reveal the bottom of the trunk so you can observe and remove any sprouts that emerge from below the graft.  Having a clear span on the bottom of the trunk will also allow you to protect the graft if a hard freeze threatens.

Harvesting
Avocados ripen over long period of time beginning in late summer through early fall – August through October, depending on variety and the weather.  Avocados do not ripen to table quality on the tree. They must be harvested and allowed to ripen on the kitchen counter.

Test maturity by picking a few and setting them on the counter. Ripe avocados will soften in 3 – 8 days. Immature fruit will not soften – it will turn rubbery or it will shrivel up. If the first fruits do not soften, test every week until they do. Once they have reached that stage, you can begin harvesting the largest fruits, leaving the smaller ones to continue to mature. Fruit can be stored on the tree for quite awhile if the temperatures are cool. The best harvesting time is when temps are in the 70’s. The oils in avocados can become rancid on the tree if they become overripe and they will generally fall at that point. Discard those fruits.

Freeze Protection
Avocados will need to be protected from frosts and freezes for their first few years. When a frost is predicted, drape the young tree with freeze cloth, a sheet, or cloth tarp. Do not use any plastic.

If a severe freeze is predicted, you will need to consider protecting the graft. Mound soil around the young tree, covering the graft. Then mound additional mulch around graft union. Be sure to remove this material in a timely manner after the cold weather has passed. Drape the tree with several layers of frost cloth, a blanket, quilt, or cloth tarp. Do not wrap the tree. Anchor the bottom of the protective material to the ground leaving a wide “skirt”. The radiant heat from the exposed ground under the tree will help protect the tree. You can add Christmas lights under the skirt if you wish.

Spraying with Bonide “Wilt-Stop” will add several degrees of frost protection. It is a natural product made from pine resin. The other option, “Cloud Cover” is not organic-approved. Once the tree has matured, it should withstand our normal winters without much protection. There may be slight damage to the branch tips and leaves, but the tree will bounce back as soon as the weather moderates.  Regular foliar feeding with seaweed extract will also contribute some cold tolerance.  Foliar feeding is also a good way to deliver minor nutrients.

Avocado problems
Avocados don’t have a lot of problems. The number one concern is root rots. Good drainage, an organic soil program, and careful watering practices can reduce the chance of root rot.

Tip burn is a symptom of salt-laden soils or water stress (too much or too little). This can be avoided by good watering practices. Do not use synthetic fertilizers that contain salts.

Leaf drop is occasionally observed at bloom time. There is no cause for concern – new leaves will develop almost immediately.

Anthracnose is a disease of fruit nearing maturity. It appears as circular, sunken, brown to black spots on the fruits. These can be pared out so all of the fruit is not lost. It can be more severe in thin-skinned varieties.

Powdery mildew sometimes occurs during periods of high humidity. It is easily managed using 1T baking soda and 1T vinegar in 1qt water.

Avocado pests
Avocados are relatively pest free. If you observe aphids, use a stream of water from the hose to disperse them. If this is not sufficient, use an insecticidal soap or Neem oil. Be careful using oils when the sun is shining, even in cool weather.  Occasionally grasshoppers can be a summer pest. They can be kept at bay with good watering practices.

Suggested Month-by-Month Care

• January - Watch out for freezes, protect if necessary; trees still need water if sufficient rain does not fall; some fruit may remain, discard fallen fruit or harvest all remaining on the tree.  The oils in the fruit may be rancid by this time, especially if the weather has been warm.  Discard fruits with a "off" smell or taste.
• February - Start fertilizers; either cottonseed meal or balanced citrus-avocado food.
• March - Water deeply; plant new varieties mid-March; top dress established trees with compost.
• April - Prune freeze damage only after the tree has leafed out; increase watering as weather warms; freshen mulch; begin monthly foliar feeding with seaweed extract.
• May - Start regular summer watering schedule; tip burn may be sign of drought stress or of over-fertilizing.
• June - Water deeply once a week; maintain mulch.
• July - Water deeply once a week, watch for signs of sunburn, paint trunk white or provide burlap shade lean-to to prevent sunburn.
• August – Fertilize for the last time; water deeply once a week; check early varieties for ripeness.
• September - Begin decreasing watering frequency as days cool down; feed kelp meal; check fruits for ripeness.
• October - Decrease watering; continue checking for ripeness.
• November - Harvest as needed unless fruit falls; decrease watering to once a month; prepare for early frosts and freezes. Buy frost cloth, Bonide “Wilt-Stop”.
• December - Continue harvest as needed; pick up all fallen fruit. Monitor for freezing nights.

https://en.wikipedia.org/wiki/Hass_avocado
https://en.wikipedia.org/wiki/Brogden_(avocado)
http://www.plantphysiol.org/content/132/1/44.full
https://www.ars.usda.gov/research/publications/publication/?seqNo115=194969