A fertilizer is a solution for optimizing your plant’s health and growth.
What are fertilizers made of? Why do your plants need it? and how to choose the best plant food for your garden.
We presented all of these questions and more to Amanda Lander.
Amanda is an enthusiastic gardener with experience gardening in two very different climates. She has a passion for all things green and growing, especially native plants and their many uses. She tries and tests all she learns and loves to share that practical, proven knowledge with others
Amanda, could you explain what is a fertilizer?
Fertilizer is food for plants. It contains all the essential nutrients needed to grow and produce. Fertilizers can be any natural or synthetic material containing these elements.
How is fertilizer different from manure?
Fertilizer differs from manure in its nutrient content and application. Fertilizer is most often applied to the surface and contains nutrients necessary for plant growth and production in measurable amounts.
Manure is simply animal droppings. The main nutrient available in manure is nitrogen, though other nutrients are present in negligible amounts depending on the source animal’s diet. Manure should be worked into the soil to prevent nitrogen evaporation and improve soil structure.
Is there a quick reference for picking the right fertilizer?
If you simply want to start your new plants off right or notice a deficiency and need a quick fix, use the list below. Read on to learn why and how these fertilizer solutions work.
- Choose a slow-release fertilizer with a NPK value of 10-10-10 if you are unsure what to use but feel your plants need a pick-me-up.
- For leafy greens use a balanced or nitrogen-rich fertilizer such as 5-5-5 or 7-1-2. Avoid excess potassium but look for molybdenum or lime to increase nitrogen uptake.
- For fruits and vegetables, use a balanced fertilizer such as 5-5-5 and supplement the plants with a high potassium fertilizer like 10-15-10 when they begin to flower.
- For your lawn, use a high nitrogen fertilizer with a NPK value of 4-1-2 or 6-4-0.
- To fix yellowing leaves, if adjusting the watering schedule doesn’t help, apply a nitrogen-rich fertilizer with no phosphors such as 14-0-14 or add manganese to the soil.
What nutrients do plants need?
The 3 major nutrients plants need are Nitrogen, Phosphorus, and (K)Potassium. Calcium, magnesium, sulfur, and a variety of trace minerals are also vital components in food for your plants.
Fertilizers usually contain 2 or 3 of these main nutrients. Some fertilizers may also provide select micronutrients to encourage healthy plant growth in poor soils.
How does Nitrogen (N) affect plants?
Proper nitrogen levels produce vigorous leaf growth. This element is a major component of chlorophyll, which enables plants to photosynthesize. It is also necessary for the production of proteins.
How does Phosphorus (P) affect plants?
Phosphorus promotes early root formation and winter hardiness. It hastens maturity and is necessary for the process of converting sunlight into energy.
How does Potassium(K) affect plants?
Potassium increases disease resistance and helps plants form strong stems. It is associated with the production and movement of starches, sugars, and water within the plant. Potassium also aids in nitrogen absorption.
What are micronutrients?
Micronutrients are additional nutrients, also called trace minerals, necessary for plant growth. Essential trace minerals include boron, chlorine, copper, iron, manganese, molybdenum, zinc, and nickel. Just as the human body needs a small amount of salt, plants need small amounts of these elements in their food.
What is the N-P-K-ratio?
The N-P-K ratio is the relative amount of nitrogen, phosphorus, and potassium found in any fertilizer. It describes whether there is more, less, or an equal amount of each of these 3 major nutrients. The ratio helps gardeners apply the correct type of fertilizer to achieve the desired growth.
The numbers on the package represent the percentage of the material containing each major nutrient. They are always presented in the same order for easy comparison. These numbers are not the ratio but the concentration. However, we can learn the ratio from the concentration values.
Example: 20-20-20 fertilizer has a 1-1-1 ratio, an equal amount, of the 3 major nutrients. 20% of the material in the package is nitrogen, 20% of the material is phosphorus, and 20% of the material is potassium. The rest of the material (40%) is filler, which is necessary to prevent burning and over-fertilizing.
What ratios are available? What is each of them good for?
The following fertilizer ratios are commonly available and widely used by gardeners.
- 1-1-1 is an all-purpose fertilizer.
- 1-2-1 is best for rooting. It contains twice as much phosphorus as either nitrogen or potassium.
- 1-1-2, 1-2-2, and 2-1-2 are the most useful ratios for encouraging flowering and fruiting. The most important element in these ratios is potassium.
- 2-1-1 or 3-1-1 are the best ratios for leafy growth since they have more nitrogen than the others
Is it better to use a fertilizer that is more concentrated like 20-20-20 rather than 10-10-10?
It is not always better to use a more highly concentrated fertilizer. There is a greater risk of burning the roots at higher concentrations. Additionally, if using a quick-release fertilizer, much of the food may go to waste simply because your plants are unable to absorb it before it dissipates.
To build and maintain healthy soil, it is usually best to use slow-release fertilizers with low to medium concentrations at regular intervals. Highly concentrated, quick-release fertilizers are useful for quick results, such as encouraging annuals to bloom or remedying specific problems like revitalizing weak plants.
Do my plants even need fertilizer?
Your plants need fertilizer for continued healthy growth. As plants mature, they use the food available in the soil. If nutrients are not added, the soil can become depleted and unable to support future growth.
How do plants get along in nature without fertilizer?
Plants in nature do not survive without fertilizer. Natural fertilizer is available mainly through fallen leaves and animal droppings. Bugs, worms, and bacteria aid the decomposition process and make the nutrients available for plants to take in the resulting food through their roots.
Natural fertilization is the inspiration for garden composting. Many gardeners use it successfully as an all-purpose fertilizer for general plant health. However, compost can’t address specific problems in the garden because the nutrient content can’t be accurately measured.
When should you fertilize? Is there a rule of thumb?
Fertilize your plants in early spring as a rule of thumb. Plants need food at the peak of their growing cycle. For most established outdoor plants, this peak is in early spring when they are coming out of winter dormancy.
Vegetables benefit from regular slow-release fertilizers throughout the growing season. Other plants may benefit from a small jolt of nutrients to encourage green growth or profuse flowering.
Avoid applying fertilizer to new plants that are not yet established to prevent weak or leggy growth. Do not feed your plants in winter while they are not actively growing.
Should I test my soil before fertilizing?
You should test your soil before fertilizing to learn which amendments to apply. Applying the wrong fertilizer can do more damage than good to your plants.
For example, if you applied high nitrogen fertilizer to untested soil that is already high in nitrogen, the excess nitrogen would evaporate, unused, or burn your plants’ roots. A lack of phosphorus would prevent healthy root development and your garden would fail. Conversely, too much phosphorus and potassium can result in high soil salt levels and negatively impact microbe activity.
Does fertilizer pH matter?
The pH of the fertilizer can affect the pH of your soil. Soil pH impacts the ability of plants to take up nutrients and the activity of beneficial microbes.
The optimum pH range for most plants is from 5.5, which is slightly acidic, to 7.0, which is neutral. The specific preferences of different plants can be met by applying the appropriate fertilizer. The main nutrient that affects soil pH is nitrogen but phosphorus also has a small effect.
Ammonium-based nitrogen fertilizers are most likely to acidify the soil. Opt for nitrate-based fertilizers if your soil tends to be too acidic and consider applying baking soda or lime to raise the pH.
How much should you fertilize? Is there a rule of thumb?
As a rule of thumb, you should apply 2-3 pounds of fertilizer to every 100 square feet of garden soil or 10 pounds for every 1,000 square feet of lawn. Be careful not to over-fertilize any plants.
How do they make fertilizers?
Synthetic fertilizers are made by complicated chemical processes using natural gas, atmospheric nitrogen, rock phosphate, potash, and sulfur.
Organic fertilizers are made from mined rock minerals and natural plant and animal materials like dried powdered blood, bone, shell, and seaweed. Often these materials are composted together or the decomposition process is sped up by drying, powdering, cooking, or steeping the ingredients in water.
What are the types of plant food available?
The main types of food for plants are organic versus synthetic, solid versus liquid, and slow-release or controlled-release versus quick-release. These categories help us understand how to use them best.
What’s the difference between organic and synthetic fertilizers?
The main difference between organic and synthetic fertilizers is that synthetic fertilizers are developed to quickly reed the plant without actually enriching the soil. They also differ in their source material and cost. Organic is arguably the better choice of food for your plants but both have their merits.
The main drawback of using organic fertilizers is that they are less concentrated than synthetic fertilizers, which means fewer nutrients per pound of material. Typically they are more expensive and slower acting but have a better long-term effect on the soil. Organic fertilizers are safe for pets and they can’t be easily over-applied, which would damage plants.
Synthetic fertilizers usually offer faster results than organic plant foods and the N-P-K ratio is more accurate. They are typically less expensive than organic fertilizers and easier to apply. Synthetic fertilizers are generally not safe for pets and must be applied judiciously to avoid burning plants but frequently enough to nourish them.
How are liquid and solid fertilizers different?
Liquid and solid fertilizers act in different time frames and are applied differently. Liquid fertilizers, which are powdered nutrients mixed with water, deliver quick access to nutrients needed by plants but they also dissipate quickly. They are best applied to the soil around established plants every few weeks.
Solid granular or powdered fertilizers can release nutrients slowly with each watering so they need to be reapplied less frequently than liquid food for plants. Solid fertilizers can be mixed into the soil before planting or sprinkled around established plants and watered into the soil.
What is Foliar Feeding?
Foliar feeding is the application of diluted liquid fertilizer to the leaves of a plant instead of the soil around it. Foliar feeding is not a replacement for building healthy soil but can benefit plants in distress. It can supplement micronutrients such as zinc which may not be present in the soil in sufficient amounts.
What fertilizers are safe for pets?
Organic fertilizers are safe for pets when used correctly. Options include seaweed, manure, compost, Milorganite, and Pet-Safe Lawn Fertilizer among others. Always follow the instructions on the packaging regarding wait times for your pets’ safety.
What fertilizers would you recommend for lawns?
Lawns cover a large, usually uniform, area and benefit from high nitrogen fertilizers for healthy green blades. Apply lawn fertilizer after the first mowing of the season.
Milorganite 0636 is an organic, slow-release, high nitrogen lawn fertilizer that also provides iron and stimulates microbes. This fertilizer only needs to be applied 4 times a year and won’t burn your lawn if over-applied. It is safe for pets and children to walk and play on after application.
Scotts Green Max Lawn Food is a synthetic high nitrogen fertilizer that produces noticeable results in as little as 3 days. This fertilizer helps your lawn grow thicker as well as greener and only needs to be applied every 6 to 8 weeks. It is also safe to walk on immediately after application.
Where can you buy fertilizers online?
The following online stores are reliable sources for fertilizer:
- Gardener’s Supply Company– specialized garden fertilizers
- Jonathon Green– lawn fertilizers
- Home Depot
- Amazon
How should you choose a fertilizer?
Choose food for your plants based on their needs and your garden or lawn goals. For fast results, use liquid or synthetic fertilizers. For long-term soil health, choose organic or slow-release plant food.
Perform a soil test to learn what the specific needs of your plants are and choose a fertilizer that provides the necessary nutrients. Remember flowering and fruiting plants will especially benefit from a boost of potassium at their peak growth. All plants will benefit from appropriate amounts of nitrogen for green growth and phosphorus for root development. Apply the correct amount of fertilizer at the correct time and enjoy your healthy productive plants!
We asked Amanda a few other questions you might find interesting: