Christian County Extension Office
Selecting and Using Fertilizers
One of the more common questions I receive is how much fertilizer do plants need and when do they need it? It should first be noted that when we look to natural areas, it’s obvious that most plants do well without added fertilizer. Nevertheless, research has shown that the addition of certain materials to the soil can sometimes cause plants to produce more fruit, grow faster, and reveal more and brighter flowers. So how do you know what your soil needs? A soil test is the only sure way of determining the amount of nutrients to add to the soil. Soil test reports make recommendations for the amount and type of fertilizer to add. This will depend on the amount of organic matter present, your soils’ natural fertility and the crop you are growing. You can get a soil test box and information sheet from the Cooperative Extension Service.
When deciding what type fertilizer to use, you basically have two choices: organic and inorganic. Organic fertilizer is derived from living plants or animal wastes and is slow to break down and be absorbed by the plants. One potential drawback of organic fertilizers is that they may not release enough of their nutrients at the right time because they depend on soil organisms for break down of the nutrient source. Soil organisms are dependent on soil moisture and temperature to be active. However, the advantage to organic fertilizers is that they increase the soil’s organic content and improve the soil’s physical structure. Some examples of organic fertilizers include: cottonseed meal, blood meal, compost, and fish emulsion. Inorganic (chemical) fertilizers are manufactured and are in ready-to-use form for plants when applied. Examples include ammonium nitrate, ammonium sulfate, super phosphate and potassium chloride. So which type should you use? Simple, if you need a quick growth response, select chemical fertilizers. If you want to improve your garden soil and are not in a rush for nutrients, select an organic fertilizer.
In general, fertilizers for trees, shrubs, and perennials should be applied in late winter or spring. This assures the nutrients will be available as these plants come out of dormancy. Fertilizing in the summer can cause disease problems in cool season lawns and encourage new growth on plants, which may be damaged by early frosts in the fall. Summer annuals and vegetables do best when fertilized after planting in April and May.
How to apply fertilizer typically depends on the formulation you purchase. As a general rule of thumb, use granular fertilizers for established plants in late winter or early spring. Apply this formulation to the ground and allow it to filter into the soil. You can also ‘sidedress’ granular fertilizer 4 to 6 inches from vegetable rows and then till it into the soil. Slow-release fertilizers are in a time-release form and are best for annuals, perennials and vegetables where you want to release a small amount of nutrients over a long period of time. You can use soluble fertilizers on seasonal plants, like annuals and vegetables, where the nutrients are dissolved in water and applied using a hose-end sprayer or watering can.
As you can tell, there is some thought involved in selecting a fertilizer. Regardless of your choice, be sure to read the label. The biggest mistake most people make is to believe if a little works that a lot will work better. This type of thinking is not advised because it cost more, gives no additional benefit to plants, and can contribute to pollution of our lakes and streams.