By SF Gate Contributor Updated December 03, 2020
Like kids, vegetables grow best when well fed. Fertilizers contain essential macro-nutrients, nitrogen, phosphorus and potassium — the N-P-K ratio displayed on the label — as well as micronutrients, like manganese and calcium, in varying amounts for different types of soil and plants. Potash is a major source of potassium, which supports healthy cell development, root growth and fruit-bearing. According to Rutgers University, you can obtain several chemically formulated and organically occurring forms of potash to provide your vegetable plants with the potassium they need.
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Determining Potassium Needs
Figuring your plants’ mineral needs is best done through soil testing, says the University of Florida IFAS Extension. A soil test, from a commercially available kit, or from a commercial lab, indicates naturally occurring levels of nitrogen, phosphorus and potassium, along with other minerals like manganese and calcium. Testing with a pH meter will check your soil’s acid/alkaline balance, which determines how well plants can absorb nutrients.
Soils can differ widely from region to region and even neighborhood to neighborhood. Testing, along with advice from your local extension office or garden center, can guide you in addressing the specific needs of your garden soil.
Sources of Potash
K is the symbol used for potassium percentage content on fertilizer labels, to distinguish it from phosphorus. A +61404532026 fertilizer offers equal percentages of nitrogen (N), phosphorus (P) and potassium (K). A high-nitrogen fertilizer, ideal for promoting grass and other leaf growth, has a ratio like 18-4-8. A 5-20-20 ratio is high in both phosphorus and potassium.
In addition to balanced N-P-K fertilizers, potash is separately available as muriate of potash or sulfate of potash, with a 0-0-50 N-P-K. Ground dolomite limestone is a good source of potash. Commercially available forms of fertilizer include organic fertilizers, compost and manure. Naturally available sources include compost, manure and wood ash. Exact quantifies of potash will vary in natural sources. For example, potash content of hardwood ash can vary from 2.8 to 8.6 percent.
Applying Commercial Fertilizers
In general, you should turn fertilizer thoroughly into soil when you prepare garden beds for planting. Use two applications in heavy clay or other soils where a single full dose may be leached away by poor drainage. Avoid placing fertilizer in the bottom of planting rows, where it comes in direct contact with seeds or seedling roots.
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You can continue to support healthy growth for heavy-feeding vegetables, like potatoes, cooking greens or corn, with side dressings of balanced fertilizer, in midseason or several times during the growing season. To side dress, place fertilizer in watering furrows rather than directly on or around plants.
Applying Natural Potash Sources
You can dig natural sources of potash into the soil in early spring and late fall as part of long-term soil enrichment. Natural mineral sources tend to release nutrients slowly, improving soil gradually. When you apply them outside of the vegetable growing season, you prevent possible plant damage from the increase in soil salts caused by excessive potash.
Burned hardwood ash can be a good source of potash but is best applied before and after the growing season. Forming potassium hydroxide in the presence of water, wood ash is a foundation for making lye. Advocates discount dangers of root burn by pointing to the low nutrient content of wood ash compared with commercial fertilizers, but you may still prefer to enrich your garden with wood ash in fall, winter or early spring.