A recent letter which followed a farm visit to another grower and finally a phone call about planting an avocado tree from another grower. The basics of planting are often overlooked and we should revisit them to make sure we know how to do the basics.
The letter:
I am going to plant some avocado trees on a slope. I will be drilling a hole with an 18 inch auger about three feet deep.
I have lots of wood chips from avocado trimmings. Should I mix some avocado wood chips with the soil to insure good drainage when I plant the new trees?
Or should I mix in some compost to help good drainage? Some areas here have poor drainage because of clay soil.
The response:
DO NOT put anything in the planting hole. It makes drainage worse. And if its not fresh the decomposing gases will kill the roots. And gradually over time, the organic matter decomposes and the tree sinks deeper into the ground, covering the graft union and the tree dies. I[m glad you asked. Someone is spreading the word that this is how to plant. It's a disaster if you do this. DON'T. You think you are doing everything right, but it is wrong. There's physics and biology involved and a good horticulturist knows better because of experience. Mulch applied to the soil surface is not the same as organic matter – planting mix put in the hole.
And watch out for the auger. Especially in heavy soils, the auger can seal the sides of the hole, making an impenetrable surface to the roots. The sides need to be scrapped or scratched to make sure the seal hasn't been created. And don't go 3 feet deep. Go to the depth of the planting sleeve. When you go deeper, the refill soil will compact and the root ball sinks, burying the crown.
From the UCR Avocado website:
http://ucavo.ucr.edu/general/answers.html#anchor1423493
Planting
The avocado is a shallow rooted tree (most of the feeder roots are in the top 6" of soil) which needs good aeration. They do well if mulched with a coarse yard mulch. Current recommendation is to put approx 1/3 cu yd per tree when planting. When applying the mulch, be sure to stay about 6-8 inches away from the trunk of the tree. They like the soil pH around 6 - 6.5. If you can, plant your tree in a spot protected from wind and frost. Also, avocado trees typically do not do well planted in lawns so try to plant your tree in a non-lawn area.
- When should I plant my avocado tree? Avocado trees like warm ground. Ideally, they should go into the ground from March through June. If they go in during the summer there is always the risk of sun damage because the trees can't take up water very well when young.
- How big a hole should I dig? As deep as the current root ball and just as wide as the width plus a little extra so you can get your hands into the hole to plant it. Don't drop the tree into the hole, the roots don't like that, ease it into the hole. The avocado root system is very sensitive and great care should be taken not to disturb the root system when transplanting. If the tree is root bound, however, loosen up the soil around the edges and clip the roots that are going in circles.
- Should I put some gravel, crushed rock or planting mix at the bottom of the hole? No. Do not put gravel or anything else like planting media in the hole. The sooner the roots get out into the bulk soil, the better the tree will do. Planting mix creates a textural difference between the root ball and the bulk soil and causes water movement problems. Remember, there are 5 million acres of tree crops in California planted without planting mix.
- I have a heavy clay soil. Should I elevate the tree in a mound for better drainage? Yes, good idea. Make the mound 1 to 2 feet high and 3 to 5 feet around. Put down 20 pounds of gypsum spread 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.
- What do you mean by a "coarse yard mulch" and where can I get some? Redwood bark will work and maybe cocoa bean husks and shredded tree bark. Need something that is woody and about 2 inches in diameter. 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 your tree (like root rot). Another source of coarse mulch would be a tree trimming operation, like Asplundh or Davy. They usually have material that has been pruned from the tops of trees and doesn't contain any diseased roots. Just go through the yellow pages looking for tree services.
These directions hold true of all trees, citrus, avocado, mango..............And for a nice discussion of avocado planting and root rot, go to:
http://www.avocadosource.com/journals/avoresearch/avoresearch_02_01_2002.pdf
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