Fertlizer Blends and What They Mean

Fertilizing

It is the time to start your shrub and tree fertilizing program. All plants need food through out the year…spring, summer, fall, and even winter! Just how much and how often depends on a lot of factors, which I will address in my next blog.

Let’s start with just what the heck the numbers mean in a fertilizer blend. When selecting a fertilizer – whether it’s for annuals, vegetable gardens, trees and shrubs, perennials or lawns – the first question to answer is, “What analysis do I need?” The analysis is actually the three large numbers you see on every fertilizer label – put there by law – such as 10-20-10 or 10-10-10 or 21-7-14. These numbers represent the percentage (by weight) of the three major nutrients required for healthy plant growth, always in the same order: Nitrogen-Phosphorus-Potassium (N-P-K). Each of these nutrients affects plant growth differently, and the formulation you select should depend on your specific plants, trees, or shrubs you are feeding.

The first number is the percentage of nitrogen in the mix. So a bag of 24-10-0 has 24 percent total nitrogen. Nitrogen provides plants with the ability to produce more chlorophyll, which in turn allows plants to grow quickly. With each additional nitrogen application, plants will grow taller and develop a darker green color. So if you want a dark green lawn, use a lawn fertilizer that’s high in nitrogen – but then expect to mow more often.

The second number in the analysis is the percentage of phosphorus in the mix. For example, a bag of 10-20-20 would contain 20 percent phosphorus. Phosphorous aids in root development and increases the flowering ability and bloom size. The fertilizer industry markets high phosphorus fertilizer as bloom builder food. High-phosphorous fertilizer should be used when plants are being established in your garden – when sowing a new lawn or planting a new tree, for instance.

The third number represents the percentage of potassium found in the product. A bag of 10-10-20 has 20 percent potassium in the mix. Potassium has many functions: It guards the plant against diseases and aids in drought protection and cold tolerance. It also serves a role in improving root development and helps in the process of photosynthesis. Use a high-potassium fertilizer at the start of winter and summer to protect crops from temperature extremes or when insects and disease have caused damage to your plants.

OK, so the numbers don’t add up to 100 %, what’s up with that? That’s because there are other nutrients and filler product in fertilizer mixtures, such as Iron (which will be the fourth number in a blend). This filler helps to apply the nutrients evenly over an area. No need to do the math. The first four numbers in any blended fertilizer mix are the most important for what you are feeding.

Meanwhile, back at the farm...