Fertilizer Numbers and the Basics of Fertilizing Vegetables

How to Use Organic Fertilizer for Vegetables

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Fertilizer numbers are something that I learned about when I was a biology major in college. Both my chemistry and biology classes taught me the importance of having balanced nutrients in the soil in order to have a successful yield and healthy plants, year after year. After college, fertilizer numbers didn’t come up again until my husband and I finally found a place we could call home. The year after we moved in, we created four beautiful vegetable and herb gardens and planted a small orchard of apple trees in our side yard.

After 12 years of gardening outdoors, we decided to learn how to make a cheap greenhouse and switched to growing vegetables in pots. (Our larger outdoor gardens are now dedicated to growing staples like potatoes, onions, garlic, and herbs.) My husband was delighted to be doing more container gardening. He was so impatient for the vegetables that we planted to start growing, that he decided to use some commercial fertilizer to sort of help them along. He also figured that since we were using recycled soil from a local garden club that he would need to use fertilizer – without bothering to check on the fertilizer numbers.

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Well. Using the fertilizer didn’t exactly produce the results he wanted. After a week of faithfully using commercial fertilizer whenever he watered the vegetables, we started to notice that the leaves of many of the plants were turning brown and getting crunchy. Turns out that he had burned the leaves to a crisp by using too much fertilizer. Without checking the existing soil nutrients, he had gone overboard and, not knowing the correct fertilizer numbers, managed to kill a good number of otherwise healthy plants. Even the best potting soil from a garden supply store might need some help when it comes to balancing the pH and adding the correct nutrients for the type of vegetables you want to grow.

Fertilizer Numbers: What Do They Mean?

If you want to avoid the same gardening catastrophe that we experienced, we need to start at the beginning. Let’s talk about fertilizer numbers. What do they mean? Commercial fertilizers are labeled with three numbers – the first refers to the percentage of nitrogen, the second number refers to the percentage of phosphate and the third refers to the percentage of potash or potassium. These three nutrients are key in maintaining soil health. If you’re going to use a commercial fertilizer, you want to look for fertilizer numbers that indicate all three of these nutrients are present. Most often, you’ll see fertilizer numbers that look like 12-12-12 or 5-10-5. Doing a simple soil test before you apply commercial fertilizer can help you determine which fertilizer number you need to improve and maintain soil health. Understanding soil facts, and how to improve and maintain soil health can go a long way to having a happy, healthy garden!

Fertilizer Numbers: Organic vs. Chemical Fertilizers

Fertilizer numbers aside, the first choice you need to make when looking at fertilizers for your vegetable gardens is whether you’re going to use an organic fertilizer or a chemical (synthesized or manufactured) fertilizer. You should know the difference between each of these before choosing which one to use in your soil.

fertilizer-numbers

Organic Fertilizers

Organic fertilizers are made from things like animal manure, blood meal, cottonseed meal, granite dust and fish emulsion. These kinds of organic fertilizers will actually add more organic matter to your soil, which improves the health of the microbes living in the soil. Organic fertilizers release their micro nutrients slowly over time, which is great for the long-term health of your soil and your plants, but not so good if you’re an impatient gardener and want to see results quickly. In addition to creating a healthy environment for microbes in your soil, organic fertilizers also help to fight harmful fungus and bacteria that can damage or kill your plants.

You can use organic fertilizers in your soil for container gardening by mixing it with your potting soil before you plant your seeds and seedlings.

Because organic fertilizers are made from organic matter, they are generally less balanced than chemical fertilizers. A fertilizer made of blood meal, for instance, may have fertilizer numbers of 13-0-0, meaning that it is 13 percent nitrogen and 0 percent phosphorous and potassium. This is great if you have very acidic soil since nitrogen will help to neutralize some of the acid. Based on a simple pH test (which you can purchase at most gardening supply stores), you may need to add additional organic fertilizers that will help balance the pH of the soil.

fertilizer-numbers

Chemical Fertilizers

Chemical fertilizers are just that – chemical nutrients that have been processed in a plant and produced in either a liquid or granular form to be added to your soil. They do not improve the overall health of your soil, and in some cases, may actually leach nutrients from the soil over time. Some organic gardeners have also expressed concern over the way these kinds of fertilizers are manufactured because they use large amounts of non-renewable resources that cause more damage to the environment.

Liquid chemical fertilizers (like the one we used to kill the tomato and pepper plants in our greenhouse) are meant to be diluted with water. Use the liquid fertilizer to water around the base of the plants – never spray it on the leaves – and depending on the instructions, reapply it no more than twice a week. Liquid fertilizers tend to dissipate rather quickly, so you need to apply it continuously.

Some chemical fertilizers come in granular or pellet form, and release their nutrients slowly over time, although not as slowly as organic fertilizers. These forms of chemical fertilizers are generally sprinkled around the plants in the soil, and can easily be mixed with potting soil for container gardening.

Take care when using chemical fertilizers that you don’t end up washing any excess fertilizer into nearby streams or waterways. Excessive amounts of these kinds of chemical fertilizers in water can hurt native fish and other animals, not to mention poisoning the water itself.

What Type of Fertilizer Is Right For You?

Both types of fertilizer have their place when it comes to both container gardening and growing vegetables in outdoor gardens. Make sure you check your soil pH before adding any kind of fertilizer to your vegetables, and always follow the recommendations on the label to avoid over-fertilizing your soil.

Do you have any tips to share when it comes to protecting your soil health and properly fertilizing your vegetables? Leave a comment here and share your experiences with us.

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Comments
  • Use caution when using compost, you need to know where the compost came from and what (if any) herbicides where used on it. There are some herbicides that last in the soil (and get passed in manure if they were used in a hayfield). They kill tomatoes as well as some other plants. I bought some compost based potting soil and suspect that there are traces of herbicide in it. Last year I planted tomatoes in two large pots, after transplant they immediately looked stunted with curled leaves and only got worse from there. This year I changed the soil in one pot, then put tomatoes in both. The plants in the pot with new soil look good, the ones in the original soil look like they did last year. Stunted with curled leaves. Just because the magic word ‘compost’ is used doesn’t mean it’s a superior product. Know your sources.

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