There are several organic potash sources that can provide potassium in organic vegetable gardens.
Greensand, kelp meal, and hardwood ashes are all good organic potassium sources. All are readily available.
Plants need Potassium (sometimes called potash) for plant immunity, flowering and fruiting, and potassium is critical for producing the brightly-colored pigments—like lycopene in tomatoes and leutine in corn—that are so good for us.
Use these single-nutrient organic fertilizers when your garden is deficient in potassium, but has enough nitrogen and phosphorus for healthy plant growth. If your garden needs an all-around fertilizer boost, use a good balanced organic fertilizer.
See below for application rates for these organic potash sources:
|Soil Amendment||N-P-K||Description||Lasts||Application Rate|
|Greensand||0-0-3||Iron-Potash-Silicates of marine origin. A long-term, slow-release organic potash source that gradually improves water-holding capacity in both clay and sandy soils. Can reduce watering frequency when used as part of container potting mixes.||3-5 Years|| 5-10lbs/100 sq ft
1/3 cup/10” pot
|Important source of potash & trace minerals. Excellent in seed starting mixes—boosts growth & reduces damping-off & fungal problems in seed starts. Encourages microbial populations. Contains plant growth hormones—do not over-apply!||6-12 Months|| Up to 1lb/100 sq ft
—but no more!
|Hardwood Ashes||0—1-10—0||Crushed black ash is best. Do not use near acid-loving plants, or on alkaline soils (pH greater than 6.5).||1-3 Months||1-2lbs/100 sq ft|
|Alfalfa Meal||2-1-2||A quick-release, balanced source of N, P, K, and some Sulfur. One of the best all-around organic fertilizers. Great for roses!||3-4 Months||Up to 16lbs/100 sq ft|
|Sheep Manure||0.7-0.3-0.9||Good manure source for N and K.||3-12 Months|| 1-2” layer
(10-20 5-gal buckets/100 sq ft)
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