Nitrogen – the first number in the three numbers on any fertilizer – encourages more growth. Higher levels of nitrogen produced larger plants. This is great for leafy greens.
However, in a recent study by a US agricultural college, some plants initially did better without any fertilizer. Tomato plants that were not fertilized produced fruit earlier and in greater number. Not really surprising as unfertilized plants devote all their attention to reproduction – producing fruit and seed – instead of growing more leaves. However, by the end of the growing season, fertilized tomato plants out-performed the unfertilized ones.
Another surprising result was that higher doses of phosphorus – the second number in the three on any fertilizer – didn’t necessarily produce more fruits and flowers – although that is what phosphorus is supposed to do. The study concluded that plants can only use so much phosphorus and excess amounts just go to waste and may contribute to water pollution.
Salt buildup in the soil can be an issue with liquid fertilizers. Another reason not to overdo it. Don’t add fertilizer with every watering or if you do, cut the amount of fertilizer in half.
Bottom line? Using fertilizers provides better results than not using them. Don’t overdo it: read the label and perhaps use less than recommended. When in doubt, do a soil test so you know what your plants really need.