Three nutrients in one mineral: potassium, magnesium, and sulfur — the mid-season trifecta for fruiting crops. Langbeinite is a naturally occurring evaporite mineral mined from ancient sea deposits, and it delivers all three nutrients in sulfate form that plants absorb readily without spiking pH in either direction. Unlike many potassium sources, it is pH-neutral.
 
This is the amendment to reach for when tomatoes, peppers, squash, or cucumbers are flowering and setting fruit, and you want to support that transition without a nitrogen surge that pushes leafy growth at the wrong time. Potassium drives fruit sizing, sugar development, skin quality, and disease resistance. Magnesium keeps leaves green and photosynthesis running through the long production stretch of late summer. Sulfur supports protein synthesis, enzyme function, and flavor development, particularly in alliums and brassicas.
 
Why this matters in the Pacific Northwest: Our heavy rainfall continuously leaches both potassium and magnesium from soil and container mixes. By mid-season, even well-amended beds and bags can be running short on both, and the symptoms (yellowing between leaf veins on older leaves, poor fruit set, bland flavor) are easy to misread as nitrogen deficiency and overcorrect with the wrong input. Langbeinite addresses the actual deficiency.
 
How to use:
Raised bed establishment: 2–4 lbs per 100 square feet worked into the top 6–8 inches
Container top-dress: 1–2 tablespoons per 5 gallons of mix, worked into the surface and watered in
Mid-season correction: apply at first flower and again at fruit set for tomatoes, peppers, squash, cucumbers, and melons
Blueberries and acid-loving shrubs: 1–2 tablespoons per plant annually — pH neutral, so it won't conflict with your sulfur or acidification program
Potato grow bags: use in place of or alongside gypsum for a potassium and magnesium boost without pH impact
 
How it compares to other potassium sources:
Greensand — very slow release over years, best for long-term soil building, minimal in-season impact
Soluble kelp extract — fast-acting, low concentration (17% K), best for foliar feeding and liquid applications
Langbeinite — moderate release, high concentration (22% K), best for soil incorporation and mid-season container top-dressing
 
OMRI listed for certified organic production. Granular form — easy to measure, handle, and store. Shelf life is indefinite — it is a mineral and does not degrade.