A Year of Nutrition in Citrus
By Dennis Laux, CCA –
It’s a new year, and in the citrus world, we drag 2025 into 2026 with crop harvest and farming techniques. There are a lot of different styles of farming today. Some are bare bones and some are upper-end. Today I am using the University of California, and Yara, nutrient timelines as a reference. Anyone can look these up, and they are great reference points to use for timing and products used in orchards.
The four basic phases we’re diving into are:
- Flowering
- Fruit set
- Fruit fill
- Post harvest
Flowering
Four nutrients are needed:
- Nitrogen
- Phosphorus
- Potassium
- Calcium
Nitrogen boosts yield and tree productivity. Based on soil and leaf analysis, a grower may want to alter their program to fit their specific needs. Too much nitrogen produces rank growth. Also, we are discovering in lemons, very small amounts of nitrogen (maybe zero nitrogen) can increase fruit set. The lemon tree wants to go vegetative, if there is too much nitrogen.
Phosphorus maintains long-term productivity. It is tied up very easily in the soil, so maybe a foliar application, and very active biology in the soil helps with releasing soil nutrients tied up.
Potassium promotes good early growth. It is needed for cellular function, off sets sodium levels, aids in leaf growth, pollination, and fruit set.
Calcium helps with leaf growth, pollination, and fruit set. One of the fundamental building blocks to cells, it helps make bigger cells that can increase fruit size. It counter-acts sodium in the soil. Outside of water, it is one of the most up-taken nutrients in plants. So it is very important – don’t skip the calcium!
There are other nutrients that need to be looked at including zinc, manganese, and sometimes boron. Again, a good fall soil and leaf analysis can make you money, and save you money, if you don’t need the extra nutrients.
There are several other things to think about, including plant growth regulator, cytokines, and auxins. Some growers think they work well to increase their production, and some don’t. Personally, I have seen them work.
Fruit Set
- Nitrogen
- Potassium
- Calcium
- Zinc
- Manganese
Nitrogen is a building block for trees and fruit. It turns into proteins and amino acids, which the plant uses to build cells. As the saying goes, if a little is good, more is better, but this is not the case with nitrogen! A balanced program is the only answer. As you raise the nitrogen levels, you need to raise all of the other macro nutrients, so remember, it is a balanced approach.
Potassium contributes to strong growth, stomata function, and rind quality, off-sets higher sodium cell development, and many more advantages.
Calcium helps with fruit productivity and quality.
Zinc and Manganese help with fruit set, quality, and fighting disease.
Phosphorus, though not listed above, adds energy to the plant, helps with plant stress, and helps move nutrients throughout the plant.
Check your analysis for other missing micros, iron, boron, cobalt, moly.
Fruit Fill
- Nitrogen
- Potassium
- Phosphorus
- Calcium
- Magnesium
- Zinc
- Manganese
Nitrogen is a very powerful nutrient, so use it cautiously. At this point of fruit development, monitoring the nitrogen levels is very important. More is not better – remember the balanced approach. Small doses more often are better than big slugs 2-4 times a year.
Potassium is essential for plant stress, heat and other things such as rind quality, fruit growth, and building sugars toward harvest time.
Phosphorus, the work horse of nutrients in this stage of development, offers energy for fruit growth, has a synergistic relationship with potassium, and helps the plant to overcome stress from heat and environmental factors.
Calcium provides leaf growth and tree vigor, and mitigation of sodium in the soil. It is a building block for fruit growth.
Magnesium helps with fruit fill, fruit size, rind quality.
Zinc and manganese help with fruit fill, size, and quality.
Remember, not one nutrient is the magic bullet. Balance and monitoring help to keep the tree strong and growing during stress.
There are other things to add to this mix: Cytokines help stress. Proper water management, in my opinion, a flooded orchard floor, does not help during heat. 24-hour sets, multiple times, is better than 48-to-36-hour irrigation runs. There is a ton of microbial activity going on, especially during the summer heat, when the soil temperatures are in the 70 to 80 degree range. Microbes breakdown the nutrients so the plant can take them up. Good microbes breath air, so too much water can cause stress and kill microbes. Anaerobic conditions are not good.
Post Harvest
In citrus, post-harvest nutrients are tricky, and there is never a perfect time to apply. I prefer to do a late-September-to-October Post Harvest nutrient package. Because of different varieties of citrus, early, late season, or mandarins, I prefer not to add nitrogen. My suggestion is a phosphorus, potassium, and calcium application, with essential micronutrients, such as zinc and manganese. The goal is to load the tree for next year’s spring flush. I have seen this work, and we have increased crop yields.
The other thing to think about in the growing season is work on fruit size. One fruit size can increase your yield by around 12 percent. Two fruit sizes can yield up to 20 to 24 percent increased production.
Ultra Gro sells the most available nutrients to grow a successful crop. Our potassium and phosphorus are in a class of their own. They’re plant ready and available. I have helped many growers to increase their crops and fruit sizes to maximize their returns. So, before you look at the price tag, really look at what you are purchasing. Ultra Gro applies what you need when you need it – plant-ready products, delivered on time for the specific need that your crops need, backed up with analysis to make the correct decision for your crops.
