Take a stroll through the plant fertilizer aisle at your local garden center and you’ll be met with a dizzying array of fertilizer options. Chemical or organic? Slow-release or quick release? Granular or liquid? The different types of fertilizers aren’t necessarily better than one another. They’re each meant to address certain plant growth needs. Many gardeners use a combination of fertilizer types over the course of the year. Generally, an all-purpose fertilizer is just fine for basic gardening. Some plants, such as cacti or orchids, have specific needs and may do better with a plant-specific fertilizer. Always follow manufacturer’s instructions carefully when applying fertilizer—over-fertilization burns plants.
Granular fertilizers are dry fertilizers that usually come in pellet form and must be either worked into or watered into the soil. These are applied with an automatic spreader or a fertilizer shaker container. Granular fertilizers are best suited for fertilizing larger areas. You can buy them in slow-release, controlled-release, and quick-release formulas designed to work for different amounts of time.
Slow- or gradual-release fertilizers are excellent for quick-color plants. These products feature special coatings that gradually release nutrients, usually over a period of three to nine months. The fertilizer label will clearly specify the time frame. Slow-release products frequently are already blended into bagged potting mixes, both soilless and soil-base types. If you purchase mixes that don't contain fertilizer, add it prior to planting. As the name suggests, it may take some time before you see results, but slow-release fertilizers prompt steadier growth. Midway through the growing season, if needed, you can work more slow-release fertilizer into the soil.
Granular fertilizers are also available in quick-release forms that last several weeks. These tend to be less expensive, but you’ll have to apply them more often.
Liquid Fertilizer (or Soluble Fertilizer)
Liquid fertilizers are available as powders or in bottled liquid solutions. Dissolved in water, soluble fertilizers deliver a quick nutrient burst. They're easy to handle and store and contain a high percentage of macronutrients per weight. In soil with organic matter, nutrients from a soluble fertilizer are retained. But in sandy soil or soilless mixes, nutrients move out of root zones quickly when more water washes through the soil. Most liquid fertilizers are poured onto soil. Some are sprayed onto leaves, which absorb nutrients.
Related: Evaluating Your Soil
How to Use Fertilizer and Water Together
You can apply liquid fertilizer to plants directly with your garden hose by adding a hose end sprayer attachment. The water flowing through the hose dilutes the concentrate. These are available as fixed rate sprayers, which release a set amount of fertilizer per gallon of water each time, or adjustable sprayers, which have a dial that lets you control the settings.
Organic fertilizers include compost and manure, which provide slow-release nitrogen. These fertilizers typically are used with planting beds or large containers like half-barrel planters. They improve soil structure, encourage soil microbes and earthworms, and contain a high level of micronutrients that plants need to grow. Some organic fertilizers, such as bonemeal, blood meal, or cottonseed meal, are concentrated. A small amount of these materials offers a large nutrient boost, which explains their often higher price. Although meal fertilizers are a good organic choice, they require microbes to break them down. That means they can't provide readily available nutrients during cold seasons when microbes are inactive. This is why it’s important to prepare your plants ahead of time, in the fall.
Common Fertilizer Issues
Most plants give clues when available nutrients are insufficient to fuel growth. Watch foliage carefully. When nitrogen is scarce, leaves turn yellow. Too little phosphorus causes leaves to turn reddish or purple. Older leaves burn and drop when potassium is in short supply. Other symptoms of nutrient deficiency include weak or slow growth and smaller leaves and flowers. Note that temperature shifts, insufficient light, and overwatering can also cause some of these symptoms. Troubleshoot light and watering habits first so you don’t accidentally over-fertilize your plants.