All about fertilizer – 

What Do the Numbers on Fertilizer Mean? 

NPK

The three numbers on fertilizer represents the value of the three macro-nutrients used by plants. These macro-nutrients are nitrogen (N), phosphorus (P), and potassium (K), or NPK for short. 

The higher the number, the more concentrated the nutrient is in the fertilizer. For example, numbers on fertilizer listed as 20-5-5 has four times more nitrogen in it than phosphorus and potassium. 

So now that you know what the numbers on fertilizer mean, you need to know why NPK is important to your plants. 

All plants need nitrogen, phosphorus, and potassium to grow. Without enough of any one of these nutrients, a plant will fail. 

Nitrogen (N) – Nitrogen is largely responsible for the growth of leaves on the plant. If too much nitrogen available the plant may grow abundant foliage, but not produce fruit or flowers.  In some cases growth may actually be stunted because the plant isn’t absorbing enough of the other elements it needs.

Phosphorus (P) – Phosphorus is largely responsible for root growth and flower and fruit development. It does this by helping transfer energy from on part of the plant to another.

Potassium (K) – Potassium is a nutrient that helps the overall functions of the plant perform correctly. 

Three Additional Nutrients That Matter

Plants also need these three nutrients, but in much smaller amounts:

  1. Calcium is used by plants in cell membranes, at their growing points and to neutralize toxic materials. In addition, 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.

Organic vs. Synthetic

Do plants really care where they get their nutrients? Yes, because organic and synthetic fertilizers provide nutrients in different ways. 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. In most cases, organic fertilizers and compost will provide all the secondary and micronutrients your plants need.

Synthetic fertilizers are water-soluble and can be taken up by the plant almost immediately. 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 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.

Note that the N-P-K ratio of organic fertilizers is typically lower than that of a synthetic fertilizer. This is because by law, the ratio can only express nutrients that are immediately available. Most organic fertilizers contain slow-release nutrients that will become available over time. They also contain many trace elements that might not be supplied by synthetic fertilizers.

TOMATO FERTILIZER REQUIREMENTS

In addition to NPK tomatoes also require these macronutrients

Calcium for root and leaf growth, helps produce firm tomatoes and also prevents tomato blossom end rot, a common tomato plant disease.  Additionally, it helps strengthen cell walls and therefore aids in preventing your tomatoes from cracking and splitting.

Magnesium – Magnesium deficiency is a problem where the plant looks like it has a virus with yellowing leaves, but it is caused by a lack of magnesium.  If in doubt as to the cause, treat as if it is a magnesium deficiency. It can do no harm to try!

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