Plants should be fertilized because most soil does not provide the essential nutrients necessary for optimum growth. Even if you are lucky enough to begin with great garden soil, as your plants grow, they absorb nutrients and leave the soil less fertile. Remember those tasty tomatoes and beautiful roses you grew last year? It took nutrients from the soil to build those plant tissues. By fertilizing your garden, you replenish lost nutrients and make sure that this year’s plants have the food they need to flourish.
Well-fed plants are healthier, less susceptible to disease and insect problems, more productive and more beautiful.
There are 6 main nutrients that plants require. Plants obtain the first 3 main nutrients (carbon, hydrogen and oxygen) from air and water. The other 3 are nitrogen, phosphorus and potassium.
Nitrogen helps plants create the proteins they need to produce new tissues. In nature, nitrogen is usually in short supply so plants have evolved to take up as much nitrogen as possible, even if it means not taking up other necessary elements. If too much nitrogen is available, the plant may grow abundant foliage but not produce fruit or flowers. Growth may possibly be stunted because the plant isn’t absorbing enough of the other elements it needs.
Phosphorous stimulates root growth, helps the plant set buds and flowers, improves vitality and increases seed size. It does this by helping transfer energy from one part of the plant to another. To absorb phosphorous, most plants need a soil pH of 6.5 to 6.8. Organic matter and the activity of soil organisms can also increase the availability of phosphorus.
Potassium improves overall vigor of the plant. It helps the plants make carbohydrates and gives disease resistance. It also helps regulate metabolic activities.
There are 3 additional nutrients that plants need, but in much smaller amounts:
1. Calcium is utilized by plants in cell membranes, at their growing points and to neutralize toxic materials. Additionally, calcium improves soil structure and helps bind organic and inorganic particles together.
2. Magnesium is the only metallic component of chlorophyll. Without it, plants can’t process sunlight.
3. Sulfur is a component of many proteins.
Finally, there are 8 elements that plants need in tiny amounts. These are called micronutrients and include boron, copper and iron. Healthy soil that is high in organic matter usually contains adequate amounts of all these micronutrients.
Organic vs. Synthetic
Do plants really care where they get their nutrients? Yes, because organic and synthetic fertilizers provide nutrients in another way. Organic fertilizers are made from naturally occurring mineral deposits and organic material, such as bone or plant meal or composted manure. Synthetic fertilizers are made by chemically processing raw materials.
In general, the nutrients in organic fertilizers are not water-soluble and are released to the plants slowly over a period of months or even years. For this reason, organic fertilizers are best applied in the fall so the nutrients will be available in the spring. These organic fertilizers stimulate beneficial soil microorganisms and improve the structure of the soil. Soil microbes play an important role in converting organic fertilizers into soluble nutrients that can be absorbed by your plants. Generally, organic fertilizers and compost provides all the secondary and micronutrients your plants need.
Synthetic fertilizers are water-soluble and can be taken up by the plant quickly. In fact applying too much synthetic fertilizer can “burn” foliage and damage your plants. Synthetic fertilizers give plants a quick boost but do little to improve soil texture, stimulate soil life, or improve your soil’s long-term fertility. Because synthetic fertilizers are highly water-soluble, they can also leach out into streams and ponds. Synthetic fertilizers do have some advantages in early spring. Because they are water-soluble, they are available to plants even when the soil is still cold and soil microbes are inactive. For this reason, some organically-based fertilizers, such as All-Purpose Fertilizer, also contain small quantities of synthetic fertilizers to ensure the availability of nutrients.
For the long-term health of your garden, feeding your plants by building the soil with organic fertilizers and compost is best. This will give you soil that is rich in organic matter and teeming with microbial life.