- Author: Ben Faber
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
- Author: Ben Faber
So I got an email with an attached set of photos showing a number of 18 month avocado trees that had broken at the ground line in a wind storm. It looked something like an incompatibility between scion and rootstock, since below the graft union the rootstock girth was substantially smaller than the scion. The problem is, I'd never heard of this between ‘Hass' and ‘Dusa' and the combination has been around for at least 15 years in trials.
So it was time to go out to the orchard and see the setting in which the trees had failed. And there was the answer. All of the trees had been planted too deeply. The trunk sleeves had been buried and the graft union was below grade and had been infected by disease organisms. The crown roots are the most active physiologically and that union area is a weak spot. Burying it encourages disease and a weak union.
The trees had been planted with an auger and over time the trees had settled into the soft earth and had been buried. The first time I had ever seen something like this was in Guatemala and Costa Rica. There growers had created these massive 3 x 3 X 3 foot holes and amended them 50% with compost. And over time, the trees had settled as the compost decomposed and the unions were covered with dirt. Occasionally you see people moving too fast when they are planting and this shows up in a few trees, not usually a whole orchard.
The lesson here, is that if you are going to err on plant depth, plant high. A few exposed roots won't hurt, and the settling problem doesn't become a problem. Of course it's best to plant just right.
Broken Trunks
The Buried Avocado Graft Union
- Author: Ben Faber
I am amazed how such a simple procedure can go so wrong. For avocado and citrus growers, it’s time to think about planting in the spring. And every spring and summer I get called out to diagnose trees that are failing. It often turns out that the trees have been planted too deeply. There are various ways of killing a tree, such as digging a hole too deeply and then backfilling. When the ground settles, it settles around the root collar and the tree suffocates. Or installing a dry root ball and then not irrigating soon enough. Or adding fertilizer to the planting hole which burns the roots. One of the major problems of lack education and supervision of the planting crew. Don’t assume that everyone knows how to plant a tree.
Deep planting can result in death of woody plants either because they rot in moisture saturated soils or they dry out. In either case, the symptoms are similar: wilting, sunscald or burnt leaves, lack of growth, leaf drop and eventual death of leaves, shoots and branches. Root balls planted below grade cause several problems at establishment. Since native soil surrounds the ball, there is an immediate problem with and interface between the two soil textures. Most container media are lighter than bulk soil, which is done to make sure there is adequate drainage in the nurse. When these soil-free media are planted in soil which is of a heavier texture, the interface does not allow the water to enter the root ball.
When trees are planted too deeply, they are much more subject to fungal cankers and other pathogens that can girdle the stem, killing it and all above ground parts. Planting slightly higher than grade will prevent this. Just look for the color, textural change between the roots and stem and dig the hole no deeper than the root ball to prevent settling. Newly planted trees can’t draw water from bulk soil, not until the roots move out into the soil will they be able to absorb water. Also planting cannot be rushed, because that’s when errors in planting occur.
- Author: Gary S. Bender
Since our last article on high-density avocados appeared in Topics in Subtropics we have had a lot of questions from growers concerning the cost of installation of such a grove. We have also had a lot of interest from potential winegrape growers who think this might be the way to go given that wine-grapes use about 25% of the amount of water per acre compared to avocados. For higher quality wines growers use less water, but harvest lower pounds/acre.
I am currently advising a student at Cal State San Marcos who is doing a cost study for removing an avocado grove and installing a winegrape planting in San Diego County. Hopefully we will have an article on that in the near future.
We don’t have a lot of experience in high density avocados but we will try to show some costs to help you decide.
Clearing an older grove can get expensive. In a study we did in 2010 we found that it cost $40/tree to cut a tree down, haul the cut wood down to a firewood stack and haul to small branches to a chipper. The old stump is usually killed with a herbicide and left in place to rot. So, just to remove a tree at 109 trees/acre may cost $4,360 per acre.
For our high density planting we will be planting Hass avocados grafted on Dusa rootstock. We are using this rootstock because it appears from several trials to be a good rootstock for resistance to avocado root rot in the well-draining hillside soils in San Diego County.
The current price is about $30/tree (plus or minus). For a 10’ x 10’ spacing we would plant about 435 trees per acre, this would be an initial cost of $13,500/acre. We are not calculating the cost of a grove road installation, and we are assuming that the entire acre would be planted.
Planting cost: digging, planting, wrapping and staking trees takes about 15 minutes per tree. This includes carrying the tree to the hole. At 435 trees per acre, this would take about 109 hrs. At $14/hr, this would cost $1526/ac. Stakes (435) at $2.25/stake would cost $979/ac.
The irrigation system installation would cost $2,660/ac. This is based on an entire system being installed in a 20 acre block, divided by 20 to get the cost per acre.
There are quite a few other costs that you can see from our complete avocado cost study, but these basic costs will get the trees in the ground (Table 1).
Table 1. Basic costs for the installation of a high density avocado grove. |
|
Trees (Hass on Dusa rootstock) |
$13,500 |
|
|
Planting (digging, planting and wrapping) |
$1,526 |
|
|
Stakes |
$979 |
|
|
Irrigation system |
$2,660 |
|
|
Total |
$18,665/acre |
If you are thinking about planting 10 acres, then you would need $186,650 in the bank to get the trees in the ground. There will be some shifting of costs because this study does not include clearing or building of grove roads, and with grove roads you will be planting less numbers of trees/acre.
Will you make more money in the long run? That is the question we are trying to answer with our high density trial in Valley Center.
Reference
Bender, G.S. and E. Takele. 2010. A guide to estimate compensation for loss of a single avocado tree. University of California Cooperative Extension county publication AV 606.
Takele, E., Bender, G.S., and M.Vue. 2011. Avocado sample establishment and production costs and profitability analysis for San Diego and Riverside counties, conventional production practices. http://coststudies.ucdavis.edu/
- Author: Gary Bender
Since our last article on high-density avocados appeared in Topics in Subtropics (Vol. 10 no. 1, Spring 2012) we have had a lot of questions from growers concerning the cost of installation of such a grove. We have also had a lot of interest from potential winegrape growers who think this might be the way to go given that wine-grapes use about 25% of the amount of water per acre compared to avocados. For higher quality wines growers use less water, but harvest lower pounds/acre.
I am currently advising a student at Cal State San Marcos who is doing a cost study for removing an avocado grove and installing a winegrape planting in San Diego County. Hopefully we will have an article on that in the near future.
We don’t have a lot of experience in high density avocados but we will try to show some costs to help you decide.
Clearing an older grove can get expensive. In a study we did in 2010 we found that it cost $40/tree to cut a tree down, haul the cut wood down to a firewood stack and haul to small branches to a chipper. The old stump is usually killed with a herbicide and left in place to rot. So, just to remove a tree at 109 trees/acre may cost $4,360 per acre.
For our high density planting we will be planting Hass avocados grafted on Dusa rootstock. We are using this rootstock because it appears from several trials to be a good rootstock for resistance to avocado root rot in the well-draining hillside soils in San Diego County.
The current price is about $30/tree (plus or minus). For a 10’ x 10’ spacing we would plant about 435 trees per acre, this would be an initial cost of $13,500/acre. We are not calculating the cost of a grove road installation, and we are assuming that the entire acre would be planted.
Planting cost: digging, planting, wrapping and staking trees takes about 15 minutes per tree. This includes carrying the tree to the hole. At 435 trees per acre, this would take about 109 hrs. At $14/hr, this would cost $1526/ac. Stakes (435) at $2.25/stake would cost $979/ac.
The irrigation system installation would cost $2,660/ac. This is based on an entire system being installed in a 20 acre block, divided by 20 to get the cost per acre.
There are quite a few other costs that you can see from our complete avocado cost study, but these basic costs will get the trees in the ground (Table 1).
Table 1. Basic costs per acre for the installation of a high density avocado grove. It is assumed that land is cleared and ready to plant. Installations of grove roads are not considered. |
|
Trees (Hass on Dusa rootstock) |
$13,500 |
Planting (digging, planting and wrapping) |
$1,526 |
Stakes |
$979 |
Irrigation system |
$2,660 |
Total per acre |
$18,665 |
If you are thinking about planting 10 acres, then you would need $186,650 in the bank to get the trees in the ground. There will be some shifting of costs because this study does not include clearing or building of grove roads, and with grove roads you will be planting less numbers of trees/acre.
Will you make more money in the long run? That is the question we are trying to answer with our high density trial in Valley Center.
Reference
Bender, G.S. and E. Takele. 2010. A guide to estimate compensation for loss of a single avocado tree. University of California Cooperative Extension county publication AV 606.
Takele, E., Bender, G.S., and M.Vue. 2011. Avocado sample establishment and production costs and profitability analysis for San Diego and Riverside counties, conventional production practices. http://coststudies.ucdavis.edu/