Plants are like people—they need nutrients to grow, and if you want really healthy plants, you have to give them the right nutrients in the right amounts.
This is true whether you’re using homemade compost, organic fertilizer or synthetic fertilizer.
Plant nutrients are divided into two main categories: major elements and micronutrients. In total, there are 16, including nine major elements and seven micronutrients (although some sources include additional micronutrients, we are sticking with the basics).
Feeding and Fertilizing Elements for Tomatoes
The nine major elements are the most important. They are used to make leaf tissue, conduct photosynthesis, stimulate flowering and fruiting, and grow your plant into the towering monster you desire. The nine major elements are:
- Carbon (C)
- Hydrogen (H)
- Oxygen (O)
- Nitrogen (N)
- Phosphorus (P)
- Potassium (K)
- Calcium (Ca)
- Magnesium (Mg)
- Sulfur (S)
1- Carbon, Hydrogen, and Oxygen
The first three (carbon, hydrogen, and oxygen) are supplied by water and air and the growing environment. These are the structural elements.
2- NPK: Nitrogen, Phosphorus and Potassium
The next three (nitrogen, phosphorus, and potassium, or NPK) are sometimes called the “fertilizer elements,” because they are the main ingredients in plant fertilizers. If you look a fertilizer label, you’ll see the NPK rating.
This number indicates how much of these three elements the fertilizer has by volume. So for example, a 10-10-10 fertilizer would have 10% each of these three elements.
Differences between organic and synthetic fertilizers
One of the major differences between organic and synthetic fertilizers is the strength of these three nutrients. Synthetic fertilizers might have as much as 30% of a particular macronutrient. That’s strong enough to seriously overdose your plant—imagine how you’d feel after eating a pound or so of salt in one sitting.
You’d feel dead. Organic fertilizers tend to have much lower concentrations of the major elements, with volumes that are typically below 5%. It’s much harder to cause nutrient burn with these mild fertilizers.
Organic fertilizers for Tomatoes
While we’re on the subject of organic fertilizers, here’s something else to chew on: there is no difference between organic nitrogen and synthetic nitrogen. Molecules are molecules, and plants use them all the same way. When you’re using organic fertilizer, you’re not supplying the plant with different nutrients. It’s all the same.
The difference is in how these two products are manufactured and the strength they are formulated at. Organic fertilizers rely on natural products, like seaweed and animal manure, while synthetic fertilizers are created in chemical plants from raw ingredients.
Tomatoes NPK Fertilizers Buying Guide
When you’re buying fertilizers for tomatoes (or any vegetable or fruit), look for one with a higher second number in the NPK rating. This fertilizer has been formulated to encourage flowering and fruiting. The first number (nitrogen) encourages strong leaf growth.
Excess NPK Impact on Tomato Plant
Plants with excess nitrogen have dark, lush foliage, but fewer and smaller fruits. With all those big, juicy leaves, they are more susceptible to insects and diseases. By contrast, the second number (phosphorus) encourages fruiting and flowering.
Vegetable fertilizers have a higher second number than first, so a 3-4-6 (like Espoma’s Tomato-Tone) is a good choice.
3- Calcium, Magnesium and Sulfur
The final three major elements (calcium, magnesium and sulfur) used to be known as secondary nutrients, but this is gradually fading from use as they are increasingly recognized as major elements.
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This is where things get trickier. These elements aren’t routinely included in vegetable and plant fertilizers, or at least you can’t always be sure. But they are crucially important to a successful harvest—tomatoes in particular have a relatively high demand for calcium, which they use to build the skin of the fruit.
Lack of Calcium Impact on Tomato
Lack of calcium results in a condition known as blossom end rot, which is a real bummer because it destroys your harvest.
Most of the tricks you run across in TomatoLand are basically ways to deliver sufficient calcium and magnesium to the plant. This is why people sprinkle powdered milk (calcium), egg shells (calcium), bone meal (calcium), Epsom salts (magnesium), and other things around their plants.
This is also why dolomite lime, or agricultural lime, is such wonderful stuff if you’re growing in acidic soil or in peat-based container mixes. It raises the pH to more optimal levels (around 6.5 for most vegetables) and it supplies calcium and magnesium naturally.