Post-Harvest Irrigation Critical for Next Season

By Ben Smith
Hortau Director of Grower Support & Advising

When I was a kid, I remember asking my dad why it is that turkeys can’t fly? He answered me with a somewhat well-known parable …

It goes: One Sunday, all the turkeys went to church. Upon arriving, they were surprised to find a guest preacher; an eagle, of all birds. The eagle stood to give his sermon and said, “Fellow Fowl, you can fly! He then proceeded to instruct the basic techniques of flight. Before long, the eagle and the entire turkey congregation were soaring and swooping above the church house. At the end of the service, after all had returned to the ground, hymns had been sung, and prayers said, the turkeys proceeded to walk home.

Normally, this story is used to expound the necessity of applying anything you learn whether from church, school, work, or elsewhere. However, I see it a little differently today. I have to ask, if there is one thing you could do to dramatically change your ways and make you much more profitable, would you do it? What if it really messed up the way you normally do things. Would you still do it?

The one change I am referring to is post-harvest irrigation of crops. In this article, specifically almonds. Shakers are so fresh in the fields that the operators are still trying to get used to running the machine again and establishing a rhythm. We are nowhere near post-harvest care, and yet I still feel the necessity to bring it up, as it has turned out to be a very difficult to change, and it’s never too early to start trying to convince you to fly.

Irrigation is difficult, much more so than we give credit. We have a ton of improvements to make, yet if I had to choose just one thing to change (out of all the things we can improve), I would choose to change the way we handle post-harvest irrigation. I am convinced, it is the single most critical and neglected stage, and therefore holds the greatest potential for pay-out.

Why Post-Harvest Irrigation Gets Neglected

Before I explain best practices, let me build the foundation of why. To do so, we need to look forward, or backward (cropping is cyclical after all) to bloom and spring time. Spring is a treacherous time for deciduous crops. Leaves are a plant’s factory  the place where all the energy needed to grow and reproduce is created.

However, a deciduous tree is expected to come out of dormancy, regrow their leaves, provide root flush, produce bloom, AND begin developing fruit, all at the same time, and without the use of its leafy factories having dropped them the previous fall. “Well…” you may be tempted to say, “the trees regrow their leaves pretty darn quick come spring.”

While true, leaves do show up quite early in the game, the leaves are so fragile and immature they can’t produce enough energy to give back to the tree. As they grow larger, they are able to produce more, however, and they really don’t begin to create enough sugars (carbohydrates) to give back to the tree until sometime in May. Being that bloom starts in mid-February, that means an almond tree must bloom, grow leaves, flush roots, and grow a nut all the way to the jelly stage (about 3 months) all without additional input from the newly forming leaves. How is it possible? It is all possible due to the efforts the trees put in in fall, or as I wish to describe it today: post-harvest.

Think about it.  A tree uses up all its resources starting spring growth and carrying it in to May. At that point, summer heat smacks down and the tree is left working through the dog days with no spare resources to develop and finish the nut and continue canopy growth. That’s asking a lot from our trees!

Eventually, harvest comes around and we shake off all of the fully-developed posterity.  At last, the tree has finished its labors… or, has it? The end of harvest tends to coincide nicely with cooler days and even cooler nights. Cooler nights signal trees to begin to ship carbohydrates for storage in the roots.  With no crop load, cooler temperatures, and fully developed leaves, the tree now has sufficient energy to do so. This is a usually overlooked, but absolutely critical crop stage. This is the period when a tree stores all the energy it will need come spring when it has to bloom, root flush, regrow leaves, and develop a nut without the aid of mature leaves.  If we stress a tree during this critical storage period, we ultimately limit the resources available for development of fruit in the coming year.

Don’t Cut Tree Production Short

I recently started dabbling in bonsai. (I love to prune, and the poor trees in my yard can only take so much, I needed more victims.) It is a fascinating art.  It amazes me that such a small tree can still look proportional.  I learned that when a bonsai-ist has a new bonsai, they repeatedly cut off the leaves that first push in the spring. They will cut off a minimum of two flushes of leaves, before letting the third flush grow out. The reason behind this relates so well to this discussion. By cutting off the first two flushes of leaves in the spring, the tree is essentially wasting energy stored in the fall. By the time the third flush grows, the tree is running low on resources and, in desperation, cuts the “cost” of growing leaves by growing smaller leaves. This is why the trees still look proportional, even though they are so small.

Almond and other tree crops can be limited the same way, being shorted an opportunity to produce and store carbohydrates in the fall. It has been shown that trees forced to drop leaves early, have smaller leaves, smaller fruit loads, and smaller fruit the following season.

Am I wrong is saying that our standard practice for little to no post-harvest irrigation is shorting trees in a similar fashion? Harvest is brutal.  No one ever wants to see a shaker or harvester again by the end. By the time harvest is finally complete, it feels like the work is done. The crop is in, holidays are just around the corner, and no one can ever predict what the winter weather will do.

Best Practices for Post-Harvest Irrigation

It is difficult to even think about taking care of our trees at this stage. That is why I can’t blame anyone for just wanting to get the work done, to landplane, apply fertilizer, gypsum, to get the pruners in, and to just forget about patching all the holes in the irrigation line so a proper irrigation can be performed. But when we overlook irrigation management, the trees pay a terrible price. They struggle to produce and store carbohydrates, and then, all too often, we add insult to injury by applying foliar zinc to try to force the leaves off early, effectively shortening the time the tree has to produce and store for the next year.

Understandable or not, how much crop are we losing by not paying more attention to post-harvest irrigation?

We can fix this. Out of necessity, almonds get extremely dry during harvest. Heavy equipment, slipping bark, and multiple varieties make it really hard to minimize stress during harvest. By the time harvest is over, the soil is beyond depleted of water, and yet the trees are still trying to pull a significant amount of water from the soil. As soon as the last nuts are up off the ground, we need to get in and put a serious amount of water on.

As soon as the last nuts are up off the ground, we need to get in and put a serious amount of water on. 

A lot depends on the irrigation system and soils, but it is a pretty good rule of thumb to expect to put 200 hours of water on with drip systems in the two weeks following the end of harvest. Or for fan jets or spinners, expect to put on 90 hours of water in the first week. I know this is a ton of water, but at the end of the day, it will be enough to fulfill the trees’ production needs all while refilling the soil profile. This is usually where I get pushback. The most common responses are, “I need to hurry and get the landplaning done before it rains.” Or, “it will be too muddy for pruners to get in.” Yes, both of those are likely to be true, but this only needs to happen once.

If you take the time to put on water to mitigate stress and refill the profile first, you can then return to a normal irrigation schedule: 48 hours per week, or so, and lessening as cooler weather brings lower ETs.  At that point all you have to do is watch your tension and apply a reasonable amount of water when it is needed. It won’t be muddy and soaked all the way into winter. With a rehydrated soil, and a normal irrigation schedule, you will have plenty of time to perform all the needed cultural practices. And at the same time, your trees will be producing like they should and will be fully recharged and ready to put on an incredible show in the spring. In the long run, it is a pretty minor adjustment. It changes the way all post-harvest practices are handled, but it gives your trees the best chance to really produce and gives you the best chance of really making it big with your next season.

Let’s not forget the eagle and the turkeys. Even though it provides no real benefit to us, the Eagle is protected from hunting, and is held with pride by all patriots. Whereas the turkey was nearly extinct until renewed interest in hunting prompted wildlife officials to begin planting more to replenish the wild population. Still, the turkey has be relegated to a once-per-year feast where it is overcooked and unappreciated, often overshadowed by cranberries and killer sweet potato casserole.

Which do you wish to be next season: the eagle that soars, or the turkey that learned to fly but never changed its ways?

ABOUT THE AUTHOR

Ben Smith is Hortau’s Director of Grower Support and Advising in California’s Central Valley. He grew up on a small dairy farm in northern Utah, where he spent most of his summers in the alfalfa and corn fields shoveling dirt, desperately trying to get the water to flood the fields evenly. He knew that there had to be a better way.

Ben went to Utah State University and received a B.S. degree in Crop Science with a minor in Soil Science. He has an extensive background working for irrigation equipment manufacturers and in large-scale production agriculture installing irrigation systems, maintaining existing systems, and scheduling irrigations over large acreages.

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