New gardeners may find garden centers and nurseries to be confusing places. There are so many choices of fertilizer that it’s overwhelming. What is the composition of those bags and bottles of fertilizer? What do the fertilizer numbers on the package mean? It might not seem like it would make much of a difference which type of soil you use for your garden, but it can actually have a pretty big impact. If we closely examine the numbers associated with plant fertilizer, we can see how it can help us create a more successful garden.
What is a plant fertilizer?
Let’s start at the beginning. A plant fertilizer can be either a chemical or a natural material that is added to the soil to increase its fertility and help the plant grow. Although your mother may have drenched her plants with a blue, water-soluble chemical fertilizer every week, you may not think you should do the same. However, there has been a significant change in attitude over the past ten years with regards to how to fertilize plants. The idea that we should focus on feeding soil instead of plants has gained traction in recent years.
Fertilize with compost first
Compost is a great plant fertilizer and soil amendment because it contains a broad diversity of nutrients essential for plant growth and acts as a great food source for soil microbes. The best way to promote optimum plant growth is by encouraging healthy, biologically active soil by adding compost to the garden every year.
There are times when our plants need more nutrition than what is provided in the compost. Instead of spreading wheelbarrows of compost, we can use less when we can’t afford it. There are a number of natural fertilizers that are easy to use and do an excellent job of feeding the soil. You can add these fertilizers to your garden at any time during the growing season. It is important to understand what is in each bag or bottle of fertilizer and how it will affect plant growth. This allows gardeners to get more value for their money while preventing excessive nutrients from polluting waterways and harming our plants.
What do fertilizer numbers mean?
Although it might be tempting to just grab the first bag of fertilizer you see, it’s important to make sure that the fertilizer you choose contains the right mix of nutrients for your particular type of lawn. Although it might be tempting to just grab the first bag of fertilizer you see, it’s important to make sure that the fertilizer you choose contains the right mix of nutrients for your particular type of lawn. The numbers on the front of a fertilizer package indicate the percentage by weight of each of the three major nutrients: nitrogen (N), phosphorus (P), and potassium (K). These are the ingredients used to make the fertilizer.
The three numbers represented on the label of every bagged or bottled fertilizer indicate the product’s nitrogen, phosphorus, and potassium content. In a ratio, the N stands for nitrogen, the P stands for phosphorous, and the K stands for potassium. The fertilizer numbers on the package represent the percentage of macro-nutrients by weight. Though plants need many different nutrients to grow, these three are used the most.
A fertilizer with the numbers 10-5-10 on the label indicates that it contains 10% nitrogen, 5% phosphorus, and 10% potassium. This means that only 25% of the bag’s weight is actual product.
How To Read Fertilizer Labels
The three letters commonly seen are N-P-K, which typically correspond to numbers. The percentage of the product that has each value can be seen in the example 5-7-4. The lower the values, the more filler there is in the product. A product with a higher percentage of the nutrient value would be miracle gro all-purpose. This product contains 2.4 lbs of nitrogen, 0.8 lbs of phosphorus and 1.6 lbs of potassium per 10 lb of product. The rest of the product is made up of ingredients that help it dissolve, be released slowly, and stay stable in solution.
Organic fertilizer numbers vs synthetic fertilizer numbers
The numbers in the N-P-K ratio for natural-based organic fertilizers are often smaller (2-3-2 or 1-1-6, for example). The label percentages for natural fertilizers are not accurate because they are based on the amount of nutrients that are available immediately, and many nutrients in natural fertilizers are not available right away. Soil microbes need time to process and release nutrients for plants. Although this may appear to be a negative thing, it is not. Instead of being released all at once, the nutrients in slow-release fertilizer are released gradually over a long period of time. This provides a steady supply of nutrients over a period of several weeks.
The study showed that organic, fish-based liquid fertilizer is much better for plants than synthetic chemical fertilizers because it releases nitrogen slowly over a period of 15 weeks. organic products may cost more, but you’ll get more nutrients and they will last longer.
What do plants use the N, P, and K in the fertilizer numbers for?
It is important to understand how plants use the three nutrients.
Nitrogen is in chlorophyll, which helps plants grow. A fertilizer high in nitrogen will cause a tomato or petunia to grow a lot of green leaves, often at the cost of flowers and fruit. It is more sensible to add the substance to a green, leafy vegetable plant, such as spinach or lettuce.
Unlike nitrogen, phosphorous is used for cell division and to generate new plant tissue. This fertilizer encourages good root growth and is effective in promoting fruit and flower production. Phosphorous is particularly important for plants whose roots are eaten, like beets, carrots, and onions, as well as for encouraging flower and fruit production. Fertilizers that contain bonemeal and rock phosphate are often recommended for use on root crops because they are both rich in phosphorous. When choosing a fertilizer, opt for one that is higher in phosphorous for plants that produce flowers, fruits, or edible roots.
This plant nutrient influences the activity of certain plant enzymes and manages a plant’s carbon dioxide uptake by determining the size of the pores on a leaf’s surface, called stomata, which gasses pass through. Potassium levels influence a plant’s heartiness and vigor.
What’s in a package of fertilizer?
While synthetic chemical based fertilizers are made from salts that are created in a factory, natural fertilizers are made from a blend of materials that occur naturally. Natural fertilizers have four main ingredient sources.
- Plant materials
- Manure materials
- Animal by-products
- Mined minerals
A combination of these ingredients in fertilizers is a great way to feed your soil when nutrients are low and you can’t add more compost.
The fertilizer numbers on the bag, in combination with the ingredient list, provides all the information you need to know about the fertilizer.
Best Ratio For Flowering Plants
The best fertilizer ratio for flowering plants is 10-5-15 or 8-12-6. The biggest difference between each option is the phosphorus and potassium. If you are using any form of mycorrhizae addition for the soil you will want to aim for the lower levels of phosphorus (10-5-15). If you are not utilizing microbe inoculants with the plants then you can use the fertilizer with higher levels of phosphate.
Microbial inoculants work with the plant to help it get more nutrients. Garden products that promote mycorrhizal growth are effective at solubilizing phosphorus. This symbiotic relationship requires energy from the plants. This means that if the plant can get phosphate that is available to it, it will not need to spend energy forming a relationship with fungi. Although the inoculant will not go to waste, it is likely to remain inactive until all the excess phosphate has been used up.
Best Ratio For Lawn Fertilizer
You want a lawn fertilizer that is high in nitrogen and low in phosphorus and potassium. This fertilizer has a high first number, which means it has a high percentage of nitrogen. This is good for a lawn that needs to be thick and green. The goal here is always going to be greenery. We should not focus on root development when looking at an established lawn.
If you are starting a new lawn or have recently installed turf, you will want to use a fertilizer with a higher potassium level. Choose a fertilizer with a lower concentration of nitrogen and a higher concentration of potassium. Approximately 9-0-2 fertilizer would be good for a new lawn.
The Best NPK Ratio For Vegetable Garden
The ideal NPK values for your garden will depend on the types of plants you are growing and the texture of your soil. The chart above suggests ranges for soil texture. If we explore the NPK values of garden vegetables, we will get a more generic view.
For Leafy Greens
A fertilizer with a high nitrogen level is ideal for leafy greens. The value can be 15-5-5 or 32-5-10. If your soil contains a lot of sand, you should use more nitrogen and potassium. We can use less nitrogen when we have clay soils. The only time this rule does not apply is when the clay soil is old. This can be determined by the color of the soil. Red clay soil is an older type of soil that has a high iron content. To learn more about it, check out the article on soil color.
A 20-5-10 fertilizer can be used if you are growing leafy greens in containers or potting soil. The reason for this is the potting soil tends to allow some nutrient loss through the water. Sandy soil has a lower water retention capacity than clay soil. Always wet your potting soil before applying fertilizer to prevent losing the fertilizer through the soil.
For Root Vegetables
The NPK ratios for root vegetables should have a lower nitrogen content overall, with a greater focus on potassium. Our goal is to achieve a bigger root and less upper foliage.
For Fruiting & Flowering Garden Plants
The NPK ratios for fruiting and flowering will be all-purpose during the vegetative stages of growth. The fruiting and flowering stage of garden plants in Canada and cold climates lasts until approximately mid-late June. We can add higher levels of phosphate and potassium after the flowering stage begins.
For Tomatoes & Peppers
The most common question about fertilizing tomatoes and peppers is about calcium and magnesium. Once they are transplanted outside, focus on using the fruiting and flowering NPK ratio regime. Fertilize your plants with a calcium magnesium fertilizer before planting them outdoors. Provide this to tomato and pepper seedlings. Potting soil growers are the exception to this rule. During the growing season, it is recommended to add lime or use a cal-mag supplement to ensure optimal plant health.
For Alliums Garlic, Leeks & Onions
The fourth number refers to Sulphur. N-P-K-S, this is VITAL to alliums and brassica species. This is what gives them their smell and flavour. If you have alkaline soil, you can lower the pH of the soil by adding elemental sulfur to it. If your soil pH is acidic or neutral, you only need to add the Sulphur-containing fertilizer to the areas where it is needed.
Fertilizer Ratio During the Seedling Stage
When the plant is a seedling, the main focus is on developing the roots and shoots. A fertilizer with higher nitrogen and phosphorus is what you should go for.
Fertilizer Ratio After Transplanting
If we have taken the proper precautions to harden off our plants, then we will mainly be focused on the roots and treating stress. Our primary nutrients will be phosphorus, potassium, and sulfur.
Fertilizer Ratio For Flowering Plants
If you want your plant to flower or it already has flowers, you should give it more phosphorus. If you are not getting enough flowers, it is probably because you are putting too much nitrogen in the soil.
Fertilizer Ratio For Stressed Plants
A plant is considered stressed if it has experience extreme temperatures, been moved to a new location, or been affected by pests or diseases. When possible, this means higher levels of potassium and sulphur.
This is an in-depth guide from a soil scientist on what fertilizer to use and when to use it. You are now prepared to give your plant the nutrient it needs when it needs them. This will help your plant to grow healthy and strong.