The best course to follow is to have your garden soil tested before you plant, then follow the recommendations given with your test results. Knowing what nutrients are needed helps cut down on the number of choices, but still leaves the decision of whether to use an organic or inorganic fertilizer up to you.
If you're able to obtain the nutrients you need from organic fertilizers, you reduce the risk of possibly harming the environment. However, if the nutrients you require cannot realistically be obtained from such sources, there's little danger in using inorganic fertilizers as long as you apply only as much as is needed.
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Granular and powdered commercial fertilizers release nutrients more quickly than organic fertilizers.
As you study the NPK (nitrogen, phosphorous, and potassium) formula on each plant food, you'll notice that organic fertilizers contain much lower percentages of nutrients per pound than do inorganic fertilizers. For the most part, this doesn't matter when feeding annuals.
Where this can become a problem is when you're trying to adjust a large garden bed's nutrient content at the beginning of the growing season. You may find that, in order to raise the nutrients to the recommended level, you'll have to add 4 inches of the organic material. This can be done if the area to be covered is small, but for large areas, it could become unwieldy. In these cases it's more practical to make major adjustments with inorganics, then proceed with organics for minor adjustments in future years.
Fertilizers are applied in a dry granular or powder form, or mixed with water for a liquid application. The granular or powder foods should be broadcast over the soil surface and dug in; liquid applications can be made with a hand sprayer or a special mixing attachment for your garden hose.
To supply food for immediate use by bedding annuals that are newly planted out, a weak solution of water soluble fertilizer -- either fish emulsion or an inorganic type -- can be poured from a watering can directly around each plant. Thereafter, a couple of side dressings of granular plant food sprinkled around each plant at two-week intervals should carry them through the rest of the summer.
For best absorption, fertilize when the soil is moist. Take care to apply it on the soil rather than on the plant leaves. The plants, your hands, and the fertilizer should be dry when you fertilize. Caution: Always wash your hands after handling fertilizer.
A final word regarding two homemade soil amenders: compost and liquid manure. Compost is made by combining plant wastes with soil and fertilizer, allowing them to decompose for several months, then mixing them back into the garden. Liquid manure is made by combining animal wastes and water, allowing them to decompose, then watering the garden with the resultant liquid. Both are good organic nutrient sources even though their level of nutrients is low. However, neither is especially practical for the average, small home garden.