How To Choose the Right Fertilizer
You know that your vegetable garden and rose bushes need some extra nourishment, but how do you go about choosing the best fertilizer? There are many varieties available, so it's good to gain some basic knowledge about fertilizers before you go shopping. (For specific information about lawn fertilization, see our Lawn Fertilizer Buying Guide.)
Because pH levels affect the ability of soil to release fertilizer nutrients, you will first need to test the pH of your soil. Luckily, testing your soil is relatively easy. At-home test kits are available and most local Cooperative Extension Services provide tests for a small fee. Before you buy fertilizer, consider the following questions:
• Do you need fertilizer for plants in containers or in your garden?
• Will you need a fertilizer that works immediately or over time?
• What do the numbers on a fertilizer package tell you?
• Have you ever applied fertilizer to your vegetable garden?
• Would an all-purpose or specialized fertilizer work better for you?
Types, Application Tips and Nutrients
Before buying fertilizer, you must first do some research on the different types available. The three-number code on the fertilizer package indicates the amount of its three primary ingredients: nitrogen, phosphorus and potassium. Different plants and vegetables need varying concentrations of these nutrients and other elements. Fertilizers are created in a range of different formulas. So, depending upon the types of plants you are working with and the soil pH, you are sure to find a formula that works well for you. Fertilizers can be applied differently, so it's best to familiarize yourself with some application tips beforehand.
Types: There are three main types of fertilizers: organic, water-soluble and synthetic. Organic fertilizers are made from natural ingredients and have a slow release, meaning that the materials in these fertilizers must be broken down by soil microorganisms for the gradual release of nitrogen and other elements. Synthetic, granular fertilizers are the most popular type and work by releasing small quantities of nutrients each time the plant is watered. Water-soluble fertilizers are easy to apply and make nutrients immediately available to plants.
• Organic fertilizers contain lower nutrient levels than other types of fertilizers and are the least likely to
cause "fertilizer burn" on plants.
• Granular, synthetic fertilizers work well for vegetables and perennials.
• Use water-soluble fertilizers with annuals and container plants.
Application Tips: Different types of plants need varying amounts of fertilizer, so make sure to follow the instructions on the fertilizer package label for best results. Work organic fertilizers into the soil before you plant, then around your plants afterward. With granular fertilizers, measure out the required amount and sprinkle lightly around the bottom of the plant, mixing the fertilizer into the soil. Mix water-soluble fertilizers with water then apply using a watering can or sprayer.
Applying too little fertilizer leaves plants undernourished, while too much can burn plants.
• Temperature affects organic fertilizers, so nutrients may be unavailable until spring or fall.
• To avoid burn from synthetic fertilizers, water thoroughly after application.
• Regular application of fertilizer results in healthier, greener leaves.
• Applying granular fertilizer in windy conditions can result in uneven application.
|Nutrients: Every fertilizer package features three numbers that indicate the percentage of primary nutrients included in the fertilizer: nitrogen, phosphorus and potassium. For example, a fertilizer showing 5-10-5 on its package has 5 percent nitrogen, 10 percent phosphorus and 5 percent potassium. Depending upon the type of plant you are fertilizing and the growth stage of the plant, look for higher or lower levels of these chemicals. Labels also indicate other chemicals, called secondary nutrients, that are included in lesser amounts. Examples include calcium, magnesium and sulfur. Even smaller amounts of nutrients, or "trace elements," are used to encourage different aspects of plant growth. Trace elements include boron, manganese, copper and zinc.|
| • Nitrogen is used in the growth stage to help plants achieve leaf growth.
• Nitrogen can damage plants, so avoid direct contact with leaves.
• Formulas higher in phosphorus stimulate root development and are used for plants
nearing the flowering or fruit stage.
• Fertilizers high in potassium enhance disease resistance and the overall vitality of plants.
• Iron is a trace element that aids in the synthesis of chlorophyll. This helps plants stay green.
|Calcium||Ca||• Improving plant vigor and
promoting growth of young
roots and shoots
|Calcium benefits tomatoes by promoting plant growth and decreasing the potential for blossom-end rot|
|Magnesium||Mg||• Regulating absorption of
plant foods and helping
|Magnesium helps distribute phosphorus throughout the plant for stronger roots and increased productivity|
|Nitrogen||N||• Green, leafy growth and plant
• Blood meal fertilizers are
applied to gardens lacking
|Lawns need high levels of nitrogen because they are constantly growing new, green leaves|
|Phosphorus||P||• Strong roots, healthy fruit
and seed formation;
|Flowers usually need a fertilizer high in phosphorus to encourage blooms|
|Potassium||K||• Vigorous growth and disease
resistance, improving overall
plant health and increasing
|Winterizing fertilizer is high in potassium to improve cold hardiness in lawns|
|Sulfur||S||• Maintaining dark green
coloring; promotes vigorous
|Azaleas, camellias, rhododendrons and blueberries require acidic soil so they do well with a fertilizer high in sulfur, magnesium and iron to encourage deep green leaf color|
|Flower: Special fertilizers are available just for flowers. Many are water-soluble, which work especially well for annuals. Flower fertilizers are typically higher in phosphorous and may contain equal amounts of nitrogen and potassium.|
|Rose: Roses need more fertilizer than any other type of landscaping plant and thrive on regular feedings of slow-release fertilizers high in nitrogen. Rose fertilizers include a special mixture of nitrogen, phosphorus and potassium to encourage continued blooming throughout the growing season.|
|Vegetable: Special fertilizers uniquely formulated for vegetables are often granular or controlled-release fertilizers that provide deep penetration into the soil where small amounts of the nutrients are released as water penetrates the soil. These types can last for three to six months, based on the variety and the amount of water in your garden. Vegetable fertilizers contain nitrogen, phosphorus and potassium.|
|Houseplant: Fertilizers designed for houseplants, also called "plant food," are typically available in granular or water-soluble forms such as crystals, liquid or spikes. You can use houseplant fertilizer to encourage plant growth, increase blooms or to simply maintain the plant's health. Houseplants are container-bound and eventually need more nutrients than they can get from their potting soil.|
|Liquid: Spray liquid fertilizer on plant leaves or pour directly on root systems, depending upon the manufacturer's instructions. Because it is water soluble, liquid fertilizer is quickly and easily absorbed into a plant's root system for an immediate boost. Liquid fertilizers quickly leach into soil so they need to be applied more frequently than other types. Liquid fertilizers that are high in phosphorus can also help prevent transplant shock.|
|All-purpose fertilizer: All-purpose fertilizer works on all flowers, vegetables, trees, shrubs and houseplants, and is appropriate for soil that is fairly balanced.|