by Sadge, at Firesign Farm
We make a big compost pile every Fall - cleaning out beneath our slat-floored chicken coop and mixing in all the fallen leaves and spent plants from the garden. Turned a time or two through the winter, by Spring I have an abundance of organic fertilizer to scratch into each garden bed as I prepare it for planting, and to spread around the perennial plants as they start waking up. Besides replacing needed plant nutrients used up each season, the compost also helps retain water in my sandy high-desert soil.
When first starting a garden, the main thing you'll want to know is if your soil is more acid or alkaline - the soil pH. Testing kits are available from gardening supply catalogs, or by professional services. Your local Co-operative Extension Office might also offer that service, or can tell you who does so locally. pH is measured on a scale from 1 to 14 - 7 is neutral, above 7 is alkaline, and below 7 is acidic. Most vegetables like pH from 6 - 7, just slightly acidic.
If your soil is too acidic (below 6), a sprinkling of lime, ground limestone, will raise the pH. For alkaline soils (above 7), adding extra organic matter such as acidic peat moss will help bring the pH down. Compost, by its very nature continues to break down incrementally years after it's first applied. By adding compost each year, the ongoing process has transformed my initially highly-alkaline desert soil to a constant neutral pH.
When you look at every fertilizer label, there will be three numbers listed, ie. 30-10-10. They refer to the percentage of three basic plant nutrients, and are always in the same order: N-P-K, Nitrogen-Phosphorus-Potassium (potash). In the example above, the remaining 50% would be inert or inactive ingredients.
Compost alone can be enough for a garden, but I like adding a bit extra to make up for anything missing, plus ensure a quick, healthy harvest in my short-season climate. General-purpose chemical fertilizers, besides being composed of possibly harmful synthetic chemicals, are also, for the most part, designed to be water-soluble. Mix them up, spray them on, (buy more) and reapply regularly. They also need lots of water - something in rather short supply here - to make them break down into a form readily available to plants. I prefer making my own general-purpose fertilizer mix from items that normally occur in nature, and then break down slowly and naturally over time.
Each Spring, I stir up a bucket of my dry fertilizer mix, adding a light sprinkling over each garden bed along with an inch of compost. That's mixed into the top 6 inches, then leveled for planting. My fertilizer mix is equal parts bloodmeal (high in nitrogen), bonemeal (phosphorus - you can also use ground phosphate rock if that is readily available to you), and greensand (potassium, plus trace minerals). Trace minerals in the soil are also necessary for optimum garden growth. Zinc, copper, molybdenum, boron, and manganese, though required in very small amounts, are vital for plant well-being, and greensand, coming from sea-bottom deposits, is a good source. Some folks use wood ash as a source of potassium. The potassium in wood ashes is in a very soluble form. Potash used to be made by leaching water through ashes, then drying to concentrate the potassium. If you want to use wood ash for a potassium source, composting the ashes first can help to keep the potassium available for your plants.
Some individual plants also get specialized attention. The blueberries need very acidic soil, so they get a light application of granular sulfur each Spring, and a mulch of pine needles and coffee grounds. What I call my "fruiting" plants - the tomatoes, peppers, okra, and eggplants - benefit from crushed eggshells (calcium) and a bit of Epsom Salts (magnesium) added to each planting hole. My bulb beds - the daffodils, hyacinths, and tulips; onions, garlic, and shallots - like an extra sprinkle of bonemeal. Feed your soil now and it will, in turn, feed you well the rest of the year.