From the Ground Up Blog

A Beginner's Guide to Plant Nutrition

A Beginner's Guide to Plant Nutrition

Written by Shelby of Farminence 

There’s no limit to the amount of nutritional information that you can find out there for humans and even our pets. But understanding the nutrition for plants can seem a little more difficult (and more like a biology class). Understanding plant nutrition is key to having healthy plants and a healthy garden. You’ll be better prepared for potential plant problems and will feel more confident in caring for your plants. If it’s been a while since you had a biology class, keep reading to get a refresher on plant nutrition.

Plant Processes

You’re aware that plants make their own food – they do this through the process of photosynthesis. During photosynthesis, plants absorb energy from the sun and use this energy to change carbon dioxide and water into a form of food. Photosynthesis occurs in the plant’s cells, in specialized compartments called chloroplasts. Fun fact: chloroplasts contain a special pigment called chlorophyll that is responsible for the green color.

Photosynthesis occurs in the leafy green parts of the plant, not the roots or stems. Photosynthesis creates a food molecule, called glucose, a type of sugar, which is the same glucose that is present in many of the foods that we eat. When plants produce glucose, they also produce oxygen as a by-product.

Unlike us, plants can’t use glucose as a source of energy. Glucose is a large molecule and has to be broken down before the plant can use it, so plants use a process called respiration to break down glucose. (Does this sound like high school biology yet?)

Respiration can seem like a tricky subject, but it’s not complicated. During respiration, plant cells take the large glucose molecules and break them down through a series of steps. The large, unusable glucose molecule is broken down into a small molecule that the plant’s cells can use for energy. This form of energy is called ATP. In order to make ATP from glucose, plants need to use oxygen and release water.

I know this sounds backwards from what you may think. Many people don’t realize that plants also use oxygen and release water. They think of plants as releasing oxygen and using up water. During photosynthesis, an abundance of oxygen is produced, so there is usually enough oxygen for respiration to take place and for the plant to release back into the atmosphere.

If you have house plants, you may have noticed tiny droplets of water forming on the tips of the leaves. These droplets aren’t from being watered. The water that you see is the result of water being released through the undersides of the leaves during respiration.

Just like humans, plants need other chemicals in order for them to complete processes to grow and stay alive. In human diets, we refer to these chemicals as vitamins and minerals. In plants, they’re simply referred to as nutrients.

Types of Plants and Nutrition

The type of plant that you’re growing will affect the type of nutrition that it needs to thrive. When we think of garden plants, there are two main categories that we can split plants into, either vegetative plants or fruiting plants. Vegetative plants are grown for their foliage and leaves. This could include vegetables like lettuce, spinach, herbs or greens. Some ornamental plants are vegetative also, like ivy, hostas, or coleus.

Fruiting plants produce flowers or fruit and have different nutrient requirements than vegetative plants. The nutrients that are needed for blooms and fruits to grow are different that nutrients needed to increase leaf growth. So, if you’re growing tomatoes, cucumbers or peppers, you’ll want to feed your plants with a fertilizer that is designed to increase bloom and fruit growth. The same thing goes for ornamental plants like petunias, geraniums or daisies. For the best blooms, you’ll want a fertilizer designed to maximize blooms.

Nutritional Differences for Fruiting and Vegetative Plants

What’s the difference between nutrition for the two?

All plants need to have plenty of leafy growth in order to survive, since that’s where photosynthesis occurs and food is created for the plant. So, there’s some overlap in plant nutrition. The key to good plant nutrition is fine-tuning feedings to support the desired plant growth.

Plants that are grown for their blooms and/or fruits will need the right nutrients to make sure that blooms are full, healthy and that fruits can develop without problems. These plants will need more phosphorus than plants grown just for their foliage. Phosphorus is a crucial nutrient that supports bloom development and fruit set. Without enough phosphorus, flowering plants will not put on blooms or create fruit.

All plants will need plenty of nitrogen and potassium, which are the other two key components of most fertilizers. These nutrients are involved with numerous processes in the plants, both vegetative and flowering plants alike.

Feeding Your Plants

Plants will get most, if not all, of their nutrients from the soil. That’s why it’s so important to make sure that your garden soil is healthy and well-amended. If you’re unsure of your garden soil’s health, use a soil testing kit to get an idea of the pH as well as the amounts of nitrogen, phosphorus and potassium in the soil. The soil pH can affect how well your plants are able to absorb nutrients. If the pH is too high or too low, plants can suffer in even the most fertile soil since they won’t be able to absorb nutrients properly.

Fertilizer

One of the most common soil amendments used by gardeners is fertilizer. Fertilizer is a quick and easy way to add nutrients to the soil and keep your plants healthy. There are a ton of options when it comes to fertilizer, so how do you know which one to choose?

Start by determining whether you want a fast-acting fertilizer or a slow-released one. Both are suitable options and can deliver nutrients to your plants. A slow-released fertilizer can take longer to provide your plant with nutrition, so if you suspect a nutrient deficiency, it’s best to use a fast-acting fertilizer to get them the nutrients they need quickly. Otherwise, for healthy plants, either option will deliver nutrients to your plants.

It’s also important that you understand what you’re looking at when you buy fertilizer. On a bag of fertilizer, you’ll notice three numbers that are separated with hyphens. These numbers indicate the amount of nitrogen, phosphorus, and potassium that is present in the fertilizer. The numbers tell you what percentage of the fertilizer is composed of each nutrient. The first number represents % nitrogen, the second number represents % phosphorus, and the last number indicates the % potassium. These numbers are called the NPK (nitrogen, phosphorus, potassium) value.

Let’s look at a couple of examples. If you purchase a 100lb. bag of flower and vegetable plant food that has an NPK value of 4-6-4, you will get a bag of fertilizer that contains 4 lbs of nitrogen, 6 pounds of phosphorus and 4 pounds of potassium. Think back to the differences between vegetative plant and flowering plant needs. Remember when I said that flowering plants need more phosphorus than vegetative plants? Most vegetable and flower plant food and fertilizer will have a slightly higher amount of phosphorus than nitrogen or potassium.

Now let’s say that you purchase a bag of lawn fertilizer. Grass isn’t going to need as much phosphorus since it’s not blooming. So, you can expect lawn fertilizer to have an NPK value of 8-2-4 or something similar. If you bought a 100lb bag of this lawn fertilizer, you’d get 8 pounds of nitrogen, 2 pounds of phosphorus and 4 pounds of potassium. Nitrogen is a key component for leaf growth, which is why there is a higher amount of nitrogen in lawn food.

You may be thinking “If I’m buying all of this fertilizer, why is there so little fertilizer actually in it? What’s the rest of the fertilizer made of?”

This is a reasonable question! Most fertilizers have other components in them that can improve the soil and ensure that the nutrients are stable and in a usable form for the plant. You can definitely purchase stronger fertilizers for your plants, but you’ll also run the risk of putting too much fertilizer into the soil and burning your plant’s roots. For the best results, look for fertilizers that contain other beneficial materials that can improve the soil’s condition.

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