From Bloom to Nuts: Maximizing Almond Nut Development
By Robert Smith, Chief Agronomist
Almond yield hinges upon the early stages of development. In just a few weeks, almond trees go through a staggering transformation as they go from dormancy to bloom, pollination, and nut set. Every pollinated bloom turns into an almond. This is when the nuts are going through rapid cell division. During this time, the number of cells being formed inside the developing kernel determines its final size and ultimately your yield potential. Once that cell division phase slows down, you can’t go back and add more cells! So, what happens now really matters.
Calcium is the most important building block for the development of strong cell walls. As new cells are formed, calcium acts as the glue to strengthen the cell walls. Phosphate is essential for energy transfer (ATP) that drives cell division. If the tree is short on either or if uptake is limited by cold soils, poor root activity, or wet conditions, kernel development can be restricted before you ever see it. The first few weeks after full bloom, nut size and ultimately yield are determined. Ensuring the availability of calcium and phosphorus during this window is a key management priority for a strong harvest.
During the first 4 to 8 weeks after full bloom, the hull (epicarp and mesocarp), the shell (endocarp), and the kernel undergo rapid growth (rapid cell division). And by late April to early May, most of the structural cells in hull and shell are largely complete; development then shifts to shell hardening and kernel growth. Once the nut has “all its cells” and transitions from cell division to cell enlargement, the capacity to take up calcium into the nut declines.
The size of the kernel is directly related to the number of cells formed during the early post-bloom period. This is an energy-demanding phase that relies heavily on phosphate for ATP production. Calcium is required both as a signal for cell division and as a structural component for cell walls. Limited calcium supplies at this time will reduce the total number of cells and ultimately the kernel size.
Plant hormones (cytokinins and auxins) also promote cell division in young, developing tissues. High cytokinin levels at bloom push bud break, bloom, and early nut growth. Auxin is associated with cell division in the developing nut. For the first 4-to-8 weeks following full bloom, anything that restricts photosynthesis or carbohydrate supply, such as defoliation, severe water stress (too much or too little), nutrient imbalance (insufficient calcium or phosphate during peak demand), or heavy disease pressure, will reduce cell division and final nut size.
Ensuring adequate availability of phosphate and calcium, along with strong early leaf area, from bloom through late April, is important if the goal is to maximize cell division and set up larger, heavier kernels at harvest.
The early stages of almond development are a decisive period that determines kernel size and overall yield. During this time, effective nutrient management and supportive environmental conditions are essential. Ultra Gro’s soluble calcium products—Calcium Soil Treatment, Cal9, and ThioPlex—along with the Synstack and Rhizoplex lines that supply plant-available phosphorus, are designed to meet the tree’s needs during this critical period.
These formulations deliver essential nutrients and biologics that strengthen soil structure, improve water retention, and support vigorous early growth. By incorporating these tools into their programs, growers can better position their orchards for strong kernel development, improved crop performance, and consistently high-quality nuts.
