Just like all living things, plants must receive nutrients to survive. In addition to light and water, they need a regular diet of minerals and other elements. Grass, flowers, trees and even weeds all compete to absorb nutrients. By applying plant food to your plants on a regular basis, you replenish those nutrients so the plants can continue to grow and produce foliage, flowers and fruit.
In nature, the soil is the source of mineral nutrients, supplemented by organic matter from dead plants and animals. In some soils these nutrients have collected for millions of years to build an enormous reservoir of fertility. The Midwest prairies are examples of such soils. Once the sod was broken, beginning in the 1850’s, prairie soil grew bountiful crops for generations without added fertilizers. Other soils, however, have been leached of their mineral nutrients by rainfall. Regions that get lots of rain in the summer, when the soil is warm and minerals leach more easily, are often infertile.
Most soils provide many, but not all, of the nutrients required by plants. In nature, only plants adapted to each soil thrive on that soil. Gardeners, however, wish to grow a variety of plants adapted to all sorts of soils. This is best accomplished by supplementing the mineral nutrients in the soil with fertilizers.
All fertilizers, whether natural or synthesized, contain some or all of the nutrient elements essential for plant growth. These elements are what make a fertilizer.
In spite of all the technical information on fertilizer labels and in this guide, fertilizing garden soil is no more complicated than adding nutrients that are missing from the soil. Plant nutrients are the same in all fertilizers. They are just packaged differently, with the nutrients in different chemical formulations to be applied differently. The differences between fertilizers lie in the mix of nutrients they contain and the way they are formulated.
What’s in Plant Food?
The three essential nutrients in plant food are nitrogen (N), phosphorus (P) and potassium (K). Each plays a role in building healthy plants. Nitrogen encourages growth of leaves and stems while phosphorus and potassium increase flowering and root growth. Most plant foods also have trace elements, small amounts of other nutrients that are needed to grow healthy, beautiful plants.
Fertilizer Labels: What N-P-K Numbers Mean
Plant foods are labeled according to the percentages of each of the ingredients they contain, always in the same order: N–P–K . The label indicates the relative amounts of the three essential nutrients with an analysis formula (for example: 15-30-15, 18-24-16, or some other combination).
Selecting a Plant Food
There are several types of plant foods. Some gardeners use more than one so that they can feed their plants most appropriately. Select what is right for your flower gardens by comparing the features and benefits of each and considering how you plan to maintain your garden. Many gardeners get excellent results using a single all-purpose plant food on every plant in their garden.
Granular Complete Plant Food
- Scatter on the surface or incorporate into the soil
- Contains a mix of instantly-available and controlled-release nutrients
- Often formulated for specific plants
- Water after spreading
Water-Soluble Plant Food
- Mix with water to apply (with a garden hose or with a watering can)
- Easy to control amount and frequency of feeding
- Feeds through plants foliage and roots
- Won’t burn plants
- Starts feeding almost instantly
- Fast results often visible in a few days
- Proven to grow more and larger flowers and vegetables
- Repeat application every other week for spectacular results
- Used by most professional growers
Slow-Release Plant Food
- Spread around plants (on top of the soil) or incorporate in the soil
- Feeds slowly and steadily for up to 3 months
- No danger of overfeeding or underfeeding
- Apply directly in planting hole
- Water in thoroughly after applying
Other types of plant food, such as fertilizer spikes, are designed for specialty situations.