Potash (or potassium), along with nitrogen and phosphorous, is present in nearly every type of commercial fertilizer. As one of the top three required nutrients for plant growth, potash encourages hardy, durable plants with healthy fruit, flowers and foliage. Maintaining soil with the proper balance of nutrients is one of the principal tasks every gardener faces. In the vegetable garden, knowing how to provide sufficient potash in the soil for healthy plant growth makes the difference between a mediocre or truly magnificent harvest.
Risks of Over and Under-Fertilizing
DDC's Vegetable Garden, an online culinary resource for local gardening, points out that symptoms of potash deficiency in the vegetable garden include, "reduced vigor, susceptibility to diseases and thin-skinned or small fruit." For those about to invest several seasons' worth of time, effort and resources into a garden, finding out at the end of the year that your plants weren't getting enough potash can be extremely discouraging. However, the risks of over-fertilizing (particularly with potash) can be disappointing and outright destructive. Knowing how often to apply potash, and what form to use, makes a huge difference during harvest time.
Obtaining Potash Naturally
M. F. Ahearn of Kansas State University's Department of Horticulture points out that the principal source of potash in nature is wood ash (though synthetic potash is available in other forms). For the natural or organic gardener, this automatically presents a problem. Wood ash can be risky for composting, often resulting in a caustic lye that is both dangerous for hands and harmful to plants. Spreading ashes over your vegetable garden may boost the potash levels significantly, but at a high cost. Natural compost or barnyard manure are better sources of comprehensive nutrition for your garden, according to Easy Garden Tips. In addition to providing a balance of nutrients to the soil, compost and manure are slow-release options that gradually provide nutrients throughout the growing season. A liquid or granular fertilizer will typically run its course within weeks, thus requiring additional applications to ensure healthy soil.
If you will be using a commercial fertilizer, you'll still need to use a little caution when attempting to boost potash levels. Gardeners that have used commercial fertilizers are accustomed to reading labels that indicate nutrients, such as 5-10-5 or 10-15-10. Potash is always the third number in the series; always keep tabs on how much potash you add to the soil. Commercial fertilizers are typically much more concentrated than organic alternatives. Since these fertilizers can actually "burn" the roots in high quantities, a regular schedule of fertilizing isn't a good practice. The trick with any fertilizing schedule is to fertilize just enough to provide the essential nutrients to the plants, and no more. Unfortunately, no one can look at a soil and guess its nutrient levels, so soil testing is a key part of your overall soil health program. Regular soil tests will enable you to choose the right fertilizers, which will give your plants exactly what they need. You'll also avoid dangerous accumulations of fertilizer, saving your plants from root damage.
Test Before Adding Potash
When deciding how often to apply potash to your vegetable garden, you'll first need to first determine how you intend to fertilize. Amending your garden soil with organic compost or manure in early spring before planting will probably provide sufficient nutrients throughout the year, while commercial fertilizers may need to be applied more often. According to the University of Rhode Island Landscape Horticultural Program, the best practice for the application of any nutrient---including potash---is performing regular soil tests during the growing season so that you stay on top of your plants' changing needs. Since plants are at risk in situations of both under and over-fertilization, the safest approach requires more than an educated guess about what the plants may need. Your local extension office or gardening store should have kits available--they're well worth the money come harvest time in the fall.