Spring Fever: When to Start Irrigating

By Ben Smith
Hortau Grower Support Specialist

I grew up in a cold climate.  Each spring I looked forward to that first smell of fresh earth that came after the snow melted and the soil warmed enough to allow for that fresh fragrance.  It was also about that time that I was suddenly hit with strong symptoms of spring fever.

You know the symptoms, someone comes in from being outside and you can smell spring on them, or you walk out into the cool sunshine and suddenly you feel the need to turn over some soil and put some plants in the ground.  As strong as I always felt those urges, I haven’t been surprised to see them in almost everyone else involved in growing crops.  This is what we do.  We care for soils and plants and there is something about the revitalization that comes after winter that recharges us and gets us fired up to get out and start helping our plants grow.

When to turn on irrigation in springAll things considered, however, spring is still a transition period.  And as is expected, transition takes time.  As explosive as almond bloom may be, and as fast as it seems leaves break from the bud and begin expanding, it still takes time for them to come to productive size and to really start their photosynthetic factories.  The rate of plant growth is determined in large part by the temperature and climate.

All the processes in the plants that contribute to growth are accelerated by heat, and hindered by cold. And so, the cool, gentle days of spring provide sanctuary as delicate seeds germinate and develop essential roots, and as trees develop energy-producing leaves and water-seeking roots.

Spring is a time for plants to get all the basic mechanics and organs in place in order to be ready when the heat comes on and they can really start being productive. While it is important for us to help promote the conditions that help our plants become productive as soon as possible, we also need to take care that our spring fever exuberance doesn’t lead us to do too much and cause more harm than good.

If a single tree were a business and we were to chart its cash flow: spring, although important, would be a period of loss where total cash (energy and nutrition) falls into the red.  It takes a great amount of energy for trees to reestablish functionality by growing all new leaves and all new feeder roots each spring, and it takes a fair amount of time for these new organs to be mature enough to carry their own weight.  That’s why post-harvest care is so important to tree health.  Each spring I see a common trend:   bloom comes, leaves begin to grow, temperatures increase a little bit, and we all get very concerned about applying water and fertilizer to our plants.

When to start irrigating in spring

It’s a natural response.  I often joke and say, “Irrigation is an emotional response.”  I do mean it as a joke.  However, there is more truth in it than any of us really want to admit, especially in the spring.  But why wouldn’t it be? Spring is in the air, leaves are emerging, it’s getting warmer, and traditional irrigation scheduling methods are frustratingly complex to calculate.  Furthermore, PCAs and CCAs are anxious to get their business going so they are beginning to pressure us to apply fertilizer.  All of this usually leads us to irrigate too much, too soon.

While it is true that when leaves emerge, trees begin to transpire.  However, what we don’t always realize is that those tiny immature leaves just aren’t capable of doing very much until they mature and harden off.  Early in the season, almost all of a plant’s resources are put toward developing structure that will allow it to be productive later in the season.  This is why we see massive vegetative growth early on and then less growth as fruit size begins to grow.  The truth of the matter is that the small light-green leaves we see right now cost the tree more than they are able to provide.  They use up resources and use more water to expand cells than they do to move water through the plant.

Water traveling through the plant and transpiring into the atmosphere is the vehicle by which nutrition, including nitrogen, is transported into the plant.  If water isn’t moving through the plant, nitrogen in the soil won’t be taken up effectively.

To summarize, at this early stage plants just don’t have the ability to use many of our inputs.  Instead, they rely on storage they’ve built up prior to dormancy to redevelop their ability to be productive.  Water and nutrition applied before the plant is ready to take it up has the potential of being leached beyond the reach of the roots, and causing damage due to overly-wet or saturated conditions.  Waiting for the optimal period may only require another week, two at the most.  But this short wait has the potential of saving you money, increasing the efficiency of fertilizers and maintaining healthy roots.

Watch this year, in a matter of a few weeks, you will notice that leaves begin to turn from light green to a dark-rich green.  This is when leaves are mature and really begin their work.  You will see it as you monitor soil tension and see a sharp increase in the amount of water used.  This is when you know that it’s time to really go after the trees and take care of them. They have moved from development into full production.

In the meantime, wait until soil tension is at an appropriately dry level and then apply water and fertilizer. 
In the meantime, wait until soil tension is at an appropriately dry level and then apply water and fertilizer.  Just take care to apply the fertilizer quickly through an irrigation so you can shut off the water at the appropriate time instead of saturating the soil in order to get all of the fertilizer out.  If needed, split the application of fertilizer rather than overwatering.  Because immature leaves do not pull a lot of water, irrigations have a tendency of staying longer in the soil.  So, mistakes in over-watering now tend to stick around in the spring and compound issues later on.

The next time spring fever has you itching to irrigate, take a moment to check your tension levels and don’t be afraid to hold off watering and trust the data. Instead, take a walk in your orchard to enjoy the perfect weather and the wonders of a new season.


Ben Smith provides grower support in California’s Central Valley for Hortau. 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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