Now with 15% Boron

The best choice for dry boron fertilizer

Ideal for bulk blending. OMRI listed. 

Get Better ROI with Organic Soil Nutrients

Granubor® is the only pure, 100% water soluble micronutrient that is engineered to meet crops’ boron demands during the growing season. Other products and minerals with a lower water solubility fail to meet these demands. As a result, Granubor has delivered a greater return on investment (ROI) for farmers than any other mineral in use today. Plus, this granuated boron material meets the stringent requirements of the bulk blended-fertilizer industry.

Application and benefits

Granubor is a granulated form of refined boron, perfect for blending into fertilizer or direct application:
  • With an average particle size of 2.8 mm, Granubor is perfect for blending, providing a minimum of segregation in bagging, transport, and application
  • Granubor’s physical form makes it an excellent choice for direct application, such as spreading under or around tree and plantation crops
  • Granubor provides gradual release or boron, for more consistent, long-lasting benefits
  • The product is highly crush resistant, limiting dust during transport, hauling, and spreading
  • Granubor contains no impurities, fillers, coatings, or added ingredients
To calculate the amount of Granubor required for a specific application, simply multiply the elemental boron by 7.0.
OMRI Listed
Granubor may be used in certified organic production, food processing, and handling according to the USDA National Organic Program Rule.

Learn more about OMRI Listed® products >

Unlike Granubor, granulated ulexite is made of raw mineral borates. These raw unprocessed minerals, typically sodium-calcium borates, contain impurities and have low water solubility, making it difficult to determine just how much boron is released into the soil and when.


Granubor is produced solely from sodium tetraborate pentahydrate, which is refined from the tincal ore found only in our Boron, California mine. As a result, the product is a sodium borate—free of calcium, which can cause boron deficiency in plants.

We refine Granubor only through physical means:
  • Crushing
  • Steam
  • Water
  • Settling
  • Crystallization
The product is never treated with chemicals or other impurities or added ingredients, fillers, or coatings.

To help guarantee its optimal average particle size of 2.8 mm, Granubor is screened between -4 and +14 mesh. With very few particles falling outside these values, the product has a uniform size distribution, similar to popular blends of prilled and granulated fertilizers. As a result, less segregation occurs during bagging, transport, and application.

Surface treatment with borate reduces degradation and dust content of Granubor. The product has a particle strength of 9 lb (4.08 kg) per granule. And no other product has a dust content of less than 2,000 ppm.

The typical flow rate of Granubor is 11 lb (4.99 kg) per minute, according to fertilizer industry standard EN 1235-1995. The product can be pneumatically transported, tipped, and conveyed.

Bulk density is 57 pounds/ft3 (913 kg/m3 ) loose or 60 pounds/ft (961 kg/m3 ) tight, with a 30° angle of repose.

Granubor is formulated to provide a slow release of boron, for long-lasting crop support during the all-important growing season.


%B Average 15.0%Inconsistent B levels
Loose Bulk Density 57.2 lb/ft3 (916 kg/m3)46.0 - 55.8 lb/ft3 (736.8 - 893.8 kg/m3)
Water Solubility 100% solubleIncomplete dissolution
Research > 30 years of worldwide field tests and researchLimited field tests
Purity No added ingredients, fillers, or coatingsCan contain high levels of arsenic, aluminum, and barium

A Minute in the Field: Granubor and Soybeans

A Minute in the Field: Granubor and Soybeans

Product Video

Dan Luepkes from Corn Warriors talks to U.S. Borax about his best practices for using Granubor on to solve boron deficiency on soybeans. Watch the video

U.S. Borax, part of Rio Tinto, is a global leader in the supply and science of borates—naturally-occurring minerals containing boron and other elements. We are 1,000 people serving 650 customers with more than 1,800 delivery locations globally. We supply around 30% of the world’s need for refined borates from our world-class mine in Boron, California, about 100 miles northeast of Los Angeles. Learn more about Rio Tinto.

Copyright © 2023 Rio Tinto. All Rights Reserved.