As we get closer and closer to spring and plants begin to come out of their winter slumber, I’d like to talk about fertilizers. There are many different types out there. I’ll talk about some basics of fertilizers. Next week I’ll talk about some of the different types that are out there, so that you can make an informed decision about which kind fits your needs this spring.
First thing to talk about with fertilizer is what’s in it. Usually a fertilizer will have a series of three numbers on it, for example 10-10-10 or 16-4-8. These numbers are percentages. The first number is always nitrogen, the second phosphorus, and the third potassium. These can be abbreviated to N-P-K, which are the symbols for these elements on the periodic table of elements. These three elements are the most important for plant growth. That’s why we make recommendations based on them. If you had a 100 lb bag of 16-4-8, that bag is 16% N, 4% P, and 8% K. Meaning in that 100 lb bag you have 16 lbs of N, 4 lbs of P, and 8 lbs of K. Now, you make be thinking, “I paid for a 100 lb bag! Why am I only getting 28 lbs of nutrients from it?!” The rest of the poundage in that bag is probably going to be some other nutrients that are needed for planted growth, but in much smaller quantities, and other inert materials that keep those nutrients in a form that’s usable by plants; there could be a special coating on the pellets that make them easier to apply as well. But now that you have this knowledge it brings up an important point, that when purchasing a fertilizer it is good to look at how much N-P-K you are getting for your money, because it will vary.
Now let’s talk about when to apply it. It’s best to apply fertilizer when plants are actively growing. Fertilizer that is applied when plants are in a dormant state can be washed away before the plants wake up and need the fertilizer. Nitrogen is very mobile in the soil, meaning that when it rains your nitrogen will likely be leached out of the soil. Phosphorus and potassium will stick around a lot longer in the soil, but can be lost by erosion. Never apply fertilizer to a stressed plant. If the plant is wilted from lack of water applying fertilizer can do more damage to the plant.
Where you apply fertilizer is important. Don’t just dump all of it at the base of the plant, instead spread it around so that the roots growing out from the plant can reach out and receive it. Applying it too heavily in one spot can result in burn or keep the plant from properly taking up water. If you’re fertilizing trees remember that tree roots extend out beyond the canopy of the leaves, so you’re going need to make that application in a wide circumference around the tree. Fertilizer left on the leaves can burn the leaves.
Knowing how much to apply is very important. Under fertilizing can leave plants underdeveloped. Over fertilizing can result in a lot of young tender growth that is susceptible to disease or insect pests. Taking a soil test and bringing it to the Extension office, to send to the lab, will tell you exactly how much fertilizer you need for what you are growing.
If you have questions about fertilizers contact your local Extension Office or email me at [email protected]