Rain!

California has been in the throws of a major drought for over a year now, and both rainfall and surface flows from the mountains have been way below average for several years in a row. The map above from the USDA’s National Drought Mitigation Center, provides a pretty good picture. Other drought related information is provided in links at the bottom of this post.

This past winter, we only had two storms that I can recall. Governor Brown declared a state of emergency on January 17.  And nary a drop of rain has hit the ground since February – until recently – TWO weekends in a row! A few weekends ago, the boys and I were so excited about the sound of thunder and feel of rain that we ran around and danced outside until soaked through. Evan made a mini-shelter of our patio furniture so he could stay out and watch the whole storm. And then the next weekend (on the day we had planned a pool party for Evan’s birthday), it rained steadily the entire day. It didn’t stop the boys from having fun at the pool! It was extremely unusual to have such a lengthy storm in the middle of summer in Southern California.

A unique microclimate exists where our little grove is located. While the surrounding areas get about 7 inches of average annual rainfall, the De Luz area usually gets twice that average. But last year, we got barely above 8 inches. But hopefully, the tide is turning. According to historical weather data, we are now 10 times the normal average for the season (which starts July 1). Of course, when the normal average for the summer is only 0.06, achieving ten times that amount is not inconceivable. We are all hoping, though, that this is a sign that we will have a wonderfully wet year. It will get all our baby trees off to a good start.

Riprap  lining to control erosion.

Riprap lining to control erosion.

Luckily as part of our redevelopment, Gary fixed a lot of the erosion issues that were happening on the property. We have a graded pad at the top of the property which had several large gullies starting to form. It’s good to take the opportunity now to implement best practices and prepare for potential rains to come (as an environmental consultant, I have to plug this! 🙂 ). The whole pad was regraded and a riprap lining was installed in the biggest problem area using rocks found while digging holes for the baby trees. Check out the result.

Evan and my mom walking down the spillway toward the baby trees.

Evan and my mom walking down the spillway toward the baby trees.

Speaking of the baby trees, they are doing well. We recently visited and they looked perky after the rains. Gary just made a third application of fertilizers for the year. He also made a second application to all our stumped trees and did another round of phosphorus injections. (See previous posts for fertilizer types and amounts, if curious). This time of year, the weeds can get big, so his crew recently did a lot of weed whacking, hand-pulling, and applied some roundup in the grove.

Some drought information links:

California Avocado Commission Water Page

California State Drought Information Page

USDA National Drought Mitigation Center

De Luz Weather Information

This is for Sonoma County, which is more heavily regulated than Riverside, but there is some good information in here for BMPs:

Sonoma County Ag BMPs

Feeding the Trees

Many people living in California may have an avocado tree in their yard or know someone who does. So when I have mentioned to friends and acquaintances that we have an avocado grove, their eyes light up with curiosity. They often ask how to improve their growth and production. As I understand, sometimes backyard avo trees are stubborn producers. I am no expert on avocado tree management. We have our grove manager, Gary, who is a living encyclopedia on the subject, to help advise us about how to increase production and we generally just nod and tell him to go ahead. But I can report to you all the stuff that Gary does and maybe some things might help your backyard tree.

I’ve talked about water (important for all trees) and phosphorus injections (important for trees infected with root rot) in previous posts. All trees also need food. So Gary supplements with fertilizer twice a year, once in fall and once in spring. In early April, the following fertilizer was applied:

The fertilizer Gary uses.

The fertilizer Gary uses.

  • 8 pounds per tree with 11-7-14+18S+1Zn+Fe, that’s ratios of 11 nitrogen, 7 phosphorus, 14 potassium, 18 sulfur, 1 zinc, and iron.
  • 4 pounds per tree with sulfate of potash (0-0-50).

All fertilizers in our grove were hand broadcast, but some fertilizers can be injected into the irrigation systems.

At the same time, each stumped and mature tree was injected again with nutra-mix P+K phosphorus acid 0-28-25. This is the same as the injections done in the fall (see previous post). So these are done twice a year. Injections are made into alternate limbs and trunks from the previous injection spots in the fall. Recall from the previous post that we are using a “cool” phosphorus acid that requires more holes, but results in less burn. The method is to drill two 7/16″ holes angled 45 degrees down, inject 1 ounce per tree, then refill each hole for a total of 2 ounces per tree. Below are some pictures of new and old injections as examples.

We have 68, 5-month-old stumped Hass trees and 97 tall, mature Hass trees. The same amounts of fertilizer and phosphorus acid injections were applied whether the trees were stumped or fully grown. This is because the root systems on the stumped trees are still as large as if they were full size trees.

These are management practices done for mature trees. We are in the process of planting new trees (in the next week!) to replace the ones we recently removed in the fall. The fertilizer regimen will be much different for those trees. Stay tuned for reports on that. In the meantime, spring was glorious when we recently visited the farm in early May. Enjoy the photo gallery of the splendor below.

Female Today, Male Tomorrow: The Curious Avocado Flower

During a recent visit to the grove in January, one of our trees was already blooming. I was shocked because no other trees on the property were blooming and wondered if it was a fluke caused by a combination of the drought and hot weather we’d been experiencing. But upon further research, I learned it is possible for Hass trees to start blooming as early as January. Although the typical bloom season is from late March to early May, timing can vary greatly depending on location in the grove. This particular tree had the trifecta going for it: located in a warmer area of the grove adjacent to a road where more light and heat from the asphalt kick starts things to action, at the top of the hill on the southwestern edge of the property where it receives long exposure to sun in the afternoon, and just behind some other trees that provide some nice windbreak from the west. Mystery solved.

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The Curious Avocado Flower

Nearly every branch on our early bloomer seemed to end in a cluster of buds and flowers similar to the picture above. One tree can blossom with up to a million flowers a year (really!), but usually produce between 100 (5,000 lbs. per acre) and 500 avocados (25,000 lbs. per acre) a year (Bender). So the next mystery was how to get them to bear more fruit (closer to the 500 range would be nice!), which led to some sleuthing on the flower structure. Although it’s not the most beautiful flower in the world, it is definitely the most curious. Each avocado flower has both male and female organs, but they function at different times. When it first opens, the flower is female, its stigma receptive to pollen, but its stamens do not shed pollen (Bergh 1974). The flower will stay open for several hours, then close overnight. The next day it will re-open as a male! The stigma no longer accepts pollen, but the stamens now shed. The picture above shows all the flowers in the female stage (the white anthers of laying flat against the petals and are not releasing pollen). The flower in the middle of the cluster looks like it is just opening. If I had returned to the same flowers the next day, all the anthers would have been erected, close to the stigma and split opened to release pollen.

Successful Pollination: The Key to High Yield

Here is San Diego, the main mode of pollen transfer is via honeybees. We have a cover crop of flowers to attract bees to the property. Fascinating research abounds on bees; I’ll have to save that for a later post. Besides pollinators, avocado trees can cross-pollinate (pollen transfer between different cultivars), close-pollinate (pollen transfer within same tree through branches touching, wind), or very rarely, self-pollinate (same flower). The idea of cross-pollination is intriguing because it involves planting a cultivar that operates on a different “sexual clock” than Hass trees. Hass trees are “Type A”, meaning the flower opens as a female in the morning of the first day and then reopens as a male in the afternoon of the second day. “Type B” cultivars’ flowers open as a female the afternoon of the first day, and then reopen as male flowers the morning of the second day. Below are some tables (borrowed from Bergh) to show how this works to allow male and female flowering stages to overlap.

Real Timing Functional Overlap
Type First Day Second Day Type Morning Afternoon
Morning Afternoon Morning Afternoon A Female Male
A Female Male B Male Female
B Female Male

Before we removed and stumped many of our trees, we had a few Fuerte cultivars (which are Type B) interspersed through the grove. We may still have some down in the ravine. The research has not sold me that it really helps increase yield. Plus, the Type B crops are not as marketable. The UC breeding program is currently researching development of Type B cultivars (Marvel and Nobel) with Hass-like properties. We will probably plant a few Type B trees in the future, but I think we will depend more heavily on attracting bees to the property. So eventually adding some hives along with our cover crop is in the plan. I’ve always wanted to have an apiary for honey production. The early blooming tree on our property was thankfully swarming with bees doing their magic!

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Clusters of flowers; also notice leaf-tip burn (see earlier post on watering)

As for most of our other remaining, non-stumped trees, they are located down a ravine with southeastern exposure. They looked pretty far from blooming, so I’d expect them to start the usual time in March. If you are curious, there are all sorts of factors that affect bloom, such as age, phenology, temperature, day length, water stress, and whether it is an “on year” or an “off year”. Avocado trees have “on” years when crops are very heavy and “off” years  when there is little or even no crop. If you want to learn more about these factors and how they affect flowering, you can find more in Dr. Gary Bender’s work.

Photos taken by Julie Ogilvie.

Bender, Gary S. Avocado Production in California. University of California Cooperative Extension, San Diego County. Book 1. Chapter 3. Available at: http://ucanr.edu/sites/alternativefruits/Avocados/Literature/.

Bergh, B.O. 1974. The Remarkable Avocado Flower. California Avocado Society Yearbook. 57: 40-41.