What is the best way to plant an avocado tree?
Give the tree what it needs: Good soil drainage, nearly full sun, ample fertility. If you have heavy soil, build a mound by mixing sand and old finished compost into the best, lightest surface soil you can scrape-up. If you soil is very heavy clay, use lots of sand! Imagine the root spread of a mature tree, and start building toward that now. A robust (2 foot tall, six feet across) planting mound is your best insurance against root rot, don’t skimp.
Plant avocados from March to June when the ground is warm. Prepare your mound and dig a hole in it so that the bottom of the root-ball sits at or above natural grade. Set the potted tree in the bottom of the hole, gently peel open the seam of our paper tree box, and remove. Fill in around the tree so as not to damage the roots, no uncomposted organic matter or fertilizer of any kind in contact with the roots. Don’t cover the top of the root-ball, but leave a lip raised around it, creating a slight basin (about a foot or two across) to irrigate into. Cover and support the new mound with lots of mulch. If your mound is smaller than you’d like, use more mulch. For fertility, it’s helpful to layer composted horse, cow, or goat manure into the mulch, so it can be watered into the root-zone. Don’t feel like you need to mix a bunch of compost or manure into the dirt, just make sure it drains, so the “tea” leaching from the rotting mulch and manure, that you have piled on top of the dirt, feed your tree. Five to ten pounds of gypsum scattered over the surface, then watered into your mound is said to be an effective incantation against (Phytophthora c.) root rot. Water the new tree thoroughly upon planting, and twice a week (to keep the whole mound damp but not saturated) throughout the first season. Sunburn is a common cause of death for young trees, so prevent it by painting exposed trunk bark with white interior latex paint diluted 50/50 with water. It’s also a good idea to bury a three or four foot stick of bamboo, 1/2″ thick, next to the root-ball when you plant your tree, then loosely tie the trunk to it in a couple places. I didn’t do this and an unexpected wind storm broke-off the 1″ trunk of my spring-grafted but gorgeous 5′ tall Edranol tree last fall. A stick and two pieces of string would have saved it, and as you can tell, I’m still a bit bitter.
Will the cold kill my avocado?
Maybe. Let’s face it: planting avocados is gambling. Here on the central coast, roughly once every ten years come winter low temperatures that would kill any un-aided young avocado tree. It thus becomes the growers’ job to stack the odds by doing the things necessary to protect the tree.
1. Choose varieties wisely. Sadly it’s like this: the more delicious the avocado, the less hardy it will be. So plant something tough (Mexicola, Zutano, Bacon) for insurance, and then gamble for flavor: Tender varieties like Queen, Sharwil, Green Gold, Edranol, Hass.
2. Plant wisely: Give the tender varieties the most favorable locations.
3. Grow the trees hard. Size matters when it comes to cold tolerance. The bigger the trunk diameter, the more cold a tree can take.
4. Protect the graft union! When a cold spell hits, the most important thing to do is to insulate the graft union (the point at the base of the tree where the rootstock was joined to the tree trunk). Use straw or sawdust or burlap sacks or rags, etc. Insulate several inches thick to 10” above the graft. This way, if your tree melts down in the cold, the graft will survive and will grow back quickly. It may be ugly for a while, but it will survive. Don’t forget to remove the insulation after the cold snap has passed.
5. Cover your tree to hold in ground heat. Floating row-crop cover works well, but so do old sheets, shower curtains, plastic bags, etc. And if you want extra insurance, run a short string of large bulb (5 watt) Christmas tree lights up the trunk. That small increase in temperature may be all the tree needs to survive.
Can I plant an avocado tree from seed?
The answer to the question is yes, but you probably don’t want to. All avocados grown commercially like Hass, Bacon, and Fuerte originally came from a tree that was grown from a seed. That seedling was discovered, recognized as a variety worth cultivating, then reproduced through grafting to make millions of trees that are all copies of that original seedling tree. Your avocado tree grown from seed may in fact produce a bounty of delicious avocados. Unfortunately, the odds are against you, and you’ll most likely end up with a tree that produces inferior fruit, or no fruit at all. The varieties grown commercially have characteristics selected from an enormous gene pool that contains many negative characteristics: stringiness, large seed, uneven ripening, intolerance to Phytophthora (a fungus that causes root rot), poor flavor, a tendency to not flower or produce fruit until 7 to 13 years after planting, poor bearing characteristics, etc. With this said, your beloved seedling may well grow into a large ornamental tree, but you may wish you had planted a recognized variety that would be lovely and ornamental as well as delivering a delicious harvest.
Can I plant an avocado tree in a container?
Yes you can. Some varieties like Gwen, Littlecado, and Holiday are naturally self-dwarfing, and can in theory be kept in a container. But it is a little like asking if you can keep an eagle in a cage; it is going to take a lot of work to keep it happy. I don’t think I’ve ever seen a bearing avocado tree in a pot. Avocado trees love to grow and spread out their feeder roots wide along the soil surface under a layer of mulch. It might work if you had a really, really big pot, otherwise their roots are just too finicky, I’ve noticed that there are websites advertising avocado trees that will bear in pots, and even encourage the owner to move it in and out of doors depending on the season. I rather doubt that one will be blessed with much fruit that way. If you want a large, attractive house plant, find a seed, sprout it, and keep it in a pot. But if you want to grow avocados, get your tree in the ground.
I only have a small space. Should I consider planting an avocado tree?
If our small space has full sun and the possibility of good drainage, then go ahead and plant an avocado tree. You’ll need a least 6’ square. There are several varieties that are either naturally dwarfing or are columnar and can be kept small. The Gwen, Sharwil, Holiday, and Littlecado are all fairly small trees. The Reed is a vigorous grower, but it grows “up” more that it grows “wide.” The Reed is also self-fertile and would be a good choice if no one nearby has a tree for cross-pollination. Avocado trees can be pruned to keep their size manageable. This is done in the winter and exposed bark areas should be whitewashed to avoid sunburn.
Do I need to plant more than one tree for pollination?
It is widely accepted that you can increase your avocado production by planting more than one type of avocado tree. The complication is that according to the rule, you cannot plant just any two trees; you need an “A” type and a “B” type. “A” type trees have female flowers open in the morning, which become male in the afternoon of the next day, “B” types open first as female in the afternoon, and then male in the morning of the next day. This is what you’re looking for; to have both male and female flowers open at the same time. However, if the average daily temperature (day and night temperatures) drops below 70°, the bloom becomes irregular and the same tree can have both male and female flowers open and available for pollination. During the spring bloom where our nursery is located, in the San Francisco Bay Area, it’s almost always below a 70 degree daily average, so it is possible to have pollination between A-flowered trees, between B-flowered trees, or between A and B-flowered trees . It’s even possible for an isolated avocado tree to pollinate itself, and set a heavy crop, but you shouldn’t count on that, unless for some reason you need to fight nature.
Biologically, the whole point of this A and B flowering strategy is to avoid self-pollination and in-bred progeny, but just climate-hacking your way around this protection doesn’t mean everything will be as you wish. It has been shown that Hass, which can be self-fruitful, will drop self-pollinated fruitlets at a much higher rate than fruitlets pollinated from some diverse pollen source. The more unrelated the suitable pollen parent, the more likely will a fruitlet hang on to achieve a state of guacamole. The Reed avocado is renown for being fairly self-fruitful, while the Gwen is famous for its picky nature, bearing well only in the presence of perfectly-timed pollinators outside the Hass family line.
So it should be said that in most parts of California, the whole A and B flower thing is less important than just having an appropriately unrelated pollination partner that blooms at about the same time.
Since it is possible for an early blooming tree to finish flowering before a late blooming variety starts, it is still possible for two different varieties to miss their match, but that would be an unlucky coincidence.
How should I feed my Avocado tree?
To grow an avocado tree so it really kicks in, follow the planting instructions, then renew the manure and mulch in your mound in early July, and then again toward the end of August. Avocados take-up nitrogen most efficiently in the summer, so this is the time to push it, but having your tree well fed going into the fall seems like exactly what we’ve always heard one shouldn’t do: “Generating a flush of tender growth in the fall will only provide more fresh wood to be slaughtered in the first hard freeze.” Leaves of avocados with high nitrogen levels have been shown to tolerate lower temps without damage than leaves with low levels of N. I have seen what happens in my yard. Avocado trees I’m really baby-ing continue growing right through all but the coldest spells, and when the hard freezes come, the tenderest tips burn back on even a protected tree, but the tree resume growth as soon as the weather warms. The unfertilized tree gets burned also, and doesn’t recover as readily. I’ve never quantified the difference, and too disorganized to ever even think of testing for nitrogen levels, but the net effect is clear: a fertilized tree comes into spring bigger and more ready to grow than the one that stalled out the previous fall.