There are two common terms that gardeners often use interchangeably. “Plant food” and “fertilizer”. From a certain angle, this makes natural sense. Plants don’t eat food, with all the vitamins and minerals they need, the way animals do. The way we do. So, when we give our plants those things, we think of it as “feeding” them.
From a plant’s point of view though, that’s not entirely accurate. The definition of plant food vs fertilizer is simply a matter of how each is made and how it’s used.
Through photosynthesis, plants prepare a diet of glucose, starches, and carbohydrates, for themselves. This is their food. But, this process begins to fail without the inclusion of specific nutrients that they look for in the soil.
Fertile, well-curated soil is rich with macronutrients like nitrogen, phosphorus, potassium, and a collection of micronutrients and trace elements. These can also be added by applying different fertilizers as soil amendments.
- Plant Food is A Naturally Occurring Process
- Fertilizer is a Nutrient Supplement
- Fertilizer is Manufactured
- Over Fertilization Can Harm Plants
- Fertilizer N-P-K Ratio
Defining Fertilizer and Plant Food
Understanding plant food vs fertilizer, how plants access them, and what they do, helps us to, what I call, garden smart. Newfound confidence is gained when the reasons behind why we do what we do in our gardens become clear.
Let’s now take a closer look at the exact difference between the two. Further on, we’ll cover how each one is accessed and used by plants.
What is Fertilizer
Fertilizer is simply a soil additive, used to enrich nutrient-poor soil. This can be found in both organic and inorganic forms. And can be a simple, easy-to-use way of changing the composition of your soil to more closely mimic that of the most fertile landscapes in nature.
There are a number of nutrients, essential to the health and vitality of plants, that they seek out in the soil. If they don’t find them, plants begin to visibly wither.
The most imperative ones are nitrogen (N), phosphorus (P), and potassium (K). Because of the importance of these three elements, fertilizer labels will prominently display the amount of each, in the form of an NPK ratio. Along with other included micronutrients and trace elements.
What is Plant Food
The reason why we need to amend and cultivate our soil with fertilizer is that plants depend on those vital nutrients to photosynthesize. Which is, to make their own food. Without them, plants can neither make food nor consume it, causing them to fail.
Plant food, by definition, is made when carbon dioxide in the air is absorbed by leaves and comes in contact with the chlorophyll cells that make our plants green. Chlorophyll requires sunlight, water, and soil nutrients to function properly.
When we water our plants, moisture is absorbed through the roots. Taking with it all the nutrients necessary to support chlorophyll function. And the collaboration between carbon dioxide and chlorophyll results in glucose and starch, a plant’s primary food source.
Differences Between Plant Food Vs Fertilizer
Another factor in plant food vs fertilizer is that plants have been making their own food since the first sprouts emerged, millions of years ago. Over time, the process of recycling nutrients back into the soil evolved.
This process begins when foliage falls from plants and trees in autumn. That material decomposes, returning vital nutrients back to the soil where those same plants and trees, or new ones, can access it.
It wasn’t until early humans began practicing agriculture that they discovered increased crop quality and yield when certain natural materials were added.
And it was only in the early 17th century that science revealed the reason for this. The connection between NPK ratios and certain natural materials, or organic fertilizers, was made.
Plant Food is A Naturally Occurring Process
In botany, plants are considered autotrophs. Which are organisms that possess the ability to produce their own food. By using sunlight, water, carbon dioxide, and nutrients to stimulate the metabolic and enzymatic processes necessary for photosynthesis and food consumption.
In the same way that healthy food gives us energy, the glucose, starches, and carbohydrates that result from photosynthesis give your plants energy.
These substances are also used to make cellulose, a biological material that goes into making new, strong plant cells. Consistent watering allows plant-made food to travel throughout the plant, keeping it healthy.
Once the foliage has fallen from outdoor plants, shrubs, and trees in autumn, photosynthesis pauses for the season. These plants keep minimal internal processes going using nutrients present in the soil.
Evergreens and houseplants, however, in a state of partial dormancy, continue to photosynthesize in winter. Thus, the need to maintain adequate light for houseplants to keep them healthy. Evergreens have naturally adapted to continue efficient photosynthesis while rationing resources, despite fewer hours of daylight.
Organically Occurring Nutrients and Minerals
Infertile soil, certain nutrients, and minerals organically occur that plants use to maintain minimal, winter processes. In warmer months, they’re used to stimulate healthy growth.
The primary nutrients are nitrogen, phosphorus, and potassium. Followed by micronutrient content with calcium, magnesium, and sulfur. Metals and minerals like molybdenum, boron, copper, and zinc finish the list. In less-than-fertile soil, nutrient supplements will need to be added to support that healthy growth.
Fertilizer is a Nutrient Supplement
The level of fertility in the soil will typically vary from place to place. Untouched, wild landscapes will, of course, be teaming with plants absolutely thriving on nutrients accessed through the natural recycling of organic material. But places that have been built upon and disturbed for years will often be less so.
If you’re faced with the task of rejuvenating your soil for the purpose of gardening, luckily there are many nutrient supplements for soil available. In both organic and inorganic fertilizer form. Remember, we’re not “feeding” our plants. We’re supplementing and replenishing missing soil nutrients.
Fertilizer is Manufactured
Store-bought fertilizers are lab-designed and manufactured to replace nutritional elements taken from the soil by plants as they grow. Even organic fertilizers need to be processed into a form that is easy to use.
Crop fertilizer research began, in earnest, back in the early 17th century. As populations grew, so did the need to increase agricultural production. That technology has evolved to where synthetic fertilizers can now be tailored to the needs of specific plants. Thus, a wide number of NPK options are available.
Inorganic fertilizers are manufactured with synthetic materials and are often cheaper than organics. But the cost of over-applying can be soil and water source contamination.
Synthetic fertilizers can result in larger crops as well as a higher yield. But these nutrients don’t always come in a form that plants can immediately absorb. Microorganisms in the soil must first convert them. This is why plants grown in soil lacking these microorganisms may seem unresponsive.
In my garden, organic fertilizers are a no-brainer. They naturally improve your soil and increase water and nutrient retention. As well as essential microorganism activity. All while providing your plants with all they need to thrive, naturally.
Organic options are a bit more pricey but the crop and soil quality that results is well worth it. As we move toward more sustainable gardening practices and demand increases, the cost of organic products will inevitably go down.
Fertilizer Liquid, Granules and Spikes
Liquid fertilizers are fast-acting, often keep pH levels balanced, and can also be used as foliar sprays when leaves show signs of deficiency.
Granules and spikes are slow-releasing options that can provide consistent nourishment for up to nine months, with the first results showing in just a couple of weeks. Carrying the added benefit of stimulating an increased resistance to disease and pests, they run little risk of root burn.
Over Fertilization Can Harm Plants
Despite the lower risk, even the gentlest fertilizers can be of harm when overused and the effects of overuse can vary. For example, when too much high nitrogen fertilizer is applied to flowering plants, energy is focused on foliage growth rather than bud formation.
Depending on the type of plant, this can result in few to no flowers on ornamentals, fruits, and vegetables.
Excessive amounts of nitrogen, or any of the other elements we’ll be discussing, will eventually cause fatal damage. Not only because plants only use so much but inorganic fertilizer compounds are salts. Too much salt in the soil will absorb water before the plant can access it.
Essential Plant Nutrients
All living things need sustenance for long-term, healthy growth and development. For plants, sustenance means access to 13 specific elements for optimal growth and flower/fruit production. These are in addition to the “food” that plants make for themselves.
Fertile soil that is curated with well-aged compost, manure, and leaf mold will already be rich in these essential plant nutrients. These can also be added manually with the help of organic or inorganic fertilizers.
For effective absorption and metabolization, however, sufficient light, heat, and water must also be supplied, in tandem with these nutrients. Keep in mind that each plant variety has its own nutritional requirements.
Macronutrients form the building blocks of every plant, shrub, and tree. They create the base from which every internal plant process stems.
Through photosynthesis, plants produce starches and carbohydrates for their own consumption. But what defines plant food vs fertilizer, like no other example, is that they can’t produce these vital nutrients, themselves. They must be found in the soil.
If you regularly amend your soil with well-aged compost and other organic materials, then it should be teaming with these much-needed nutrients. With beneficial organisms just waiting to provide them to your plants.
If not, they should be regularly added and replenished by way of either an organic or inorganic fertilizer.
Nitrogen plays a vital role in the development of healthy foliage, by fueling the production of chlorophyll. These cells give leaves and stem their green color and ensure that photosynthesized energy is available to convert starches and carbohydrates into food.
This multi-tasking macronutrient also fuels the proteins and enzymes that regulate water and nutrient uptake and disbursement. High nitrogen fertilizer is typically formulated for lawns and evergreens where foliage is the primary focus.
Magnesium is a trace element that gives plants their green color. At the heart of each chlorophyll molecule, magnesium enables foliage to harness the sun’s rays. This triggers photosynthesis and the metabolization of starches and carbohydrates.
Magnesium is one of 13 minerals found in fertile soil, but once depleted, it must be replenished for your plants to stay green and continue photosynthesizing. This can be done using both organic and inorganic compounds.
Phosphorus is essential in the process of photosynthesis. Once the chlorophyll is produced, this macronutrient triggers the energy captured by the chlorophyll to convert starches and carbohydrates into food. Another important (and more visible) function of phosphorus is the creation of abundant buds, flowers, and fruit, rather than foliage.
Phosphorus begins its work at the cellular level. Contributing to the construction of those same proteins and enzymes that nitrogen uses to regulate water and nutrients.
Potassium is responsible for the circulation of water, nutrients, and photosynthesized food throughout your plants. It also activates those proteins and enzymes that were formed using phosphorus and nitrogen to build a healthy plant structure.
High potassium can contribute to a plant’s resistance against disease and extreme heat and drought by helping them to conserve moisture. And is especially effective in encouraging large, well-formed fruit on vining crops like tomatoes, squash, and melons.
Fueled by nitrogen, sulfur is the mineral responsible for the formation of chlorophyll molecules. Making it another significant part of the photosynthesis process. It also plays an essential role in nitrogen-fixing plants like legumes and bean varieties.
Sulfur is often added to fertilizers for the purpose of lowering pH levels in the soil. Where microorganisms convert it to sulfuric acid. Thereby increasing soil acidity to benefit bloomers like hydrangeas and azaleas and many berry varieties.
Fertilizer N-P-K Ratio
Every fertilizer label reflects three numbers, separated by dashes. This is its N-P-K ratio, indicating its proportions of nitrogen, phosphorus, and potassium. For example, a 10-10-10 fertilizer NPK contains 10% nitrogen, 10% phosphorus and 10% potassium.
Every plant requires these three elements in order to thrive. Just in different proportions or NPK ratios.
Each of these macronutrients plays a unique yet vital role in cell formation, photosynthesis, nutrient distribution, and flower and fruit production. All working in tandem to create a healthy, bountiful plant. And when applied properly, they can increase soil fertility and beneficial bacteria activity, too.
Whether naturally occurring or supplemented, there are 8 earthly elements, defined as micronutrients, that plants require for optimal health. Just like people, if they don’t get their vitamins, they start to wane.
The following elements each offer unique abilities that contribute toward healthy plants. Yet, a team effort is required to create robust and thriving plants that produce high yields, exceptional crop quality, abundant blooms, and vibrant foliage. Let’s take a look at each.
Boron stimulates the growth of strong plant cells in all manner of reproductive processes like pollen tubes and viable seed formation. These processes are activated by the careful regulation of a plant’s hormone levels.
This dictates what plant parts grow up, which grow down, and also the plant’s life span.
Organic chlorine is a natural by-product of fertile soil. Together with magnesium, it contributes to controlling plant disease. With potassium, chlorine regulates the circulation of nutrients and photosynthesized food. But, this form of chlorine is very different from that used to clean pools, which would actually kill your plants.
Senescence, the process of plant aging, reduces chlorophyll in foliage to give us beautiful autumn color. Cobalt plays a vital role in foliage growth, but in proper doses can also slow the aging process to prolong summer growth.
This soil element also increases drought resistance in seeds and helps to maintain viability.
Copper is one of eight essential micronutrients required by plants for critical, enzymatic processes. With only tiny doses needed, nitrogen uses copper as the catalyst for chlorophyll production, as new leaves and stems emerge. Once flowers fade, copper steps in to assist boron in the formation of viable seeds.
Iron is a vital nutrient for most living things. Mainly for its role in life-sustaining processes, like DNA synthesis, respiration, and photosynthesis. Like copper, only small amounts are needed to be effective. Without it, chlorosis (the yellowing of leaves) may take over your plants and result in them failing.
Manganese is another metal micronutrient that contributes to critical plant processes. Like cell function and photosynthesis. It is the presence of manganese that allows nitrogen to do its job.
An important function of manganese is to send signals throughout flowering plants when successful pollination has occurred, by wildlife pollinators.
Beans, peas, and other legumes have a knack for nitrogen fixation. By working with microorganisms, and the trace metal molybdenum in the soil, these crops are able to pull nitrogen literally out of thin air (the atmosphere) and convert it into a form that they can use as a nutrient.
Photosynthesis is how plants make food for themselves. With only tiny amounts required, zinc helps plants consume that food. Without the presence of zinc in the soil, every part of the plant associated with photosynthesis, like chlorophyll production, will fail because the food produced will have nowhere to go.
Is Compost or Manure a Fertilizer?
Compost and manure are not considered fertilizers, per se. Compost and manure work to increase soil fertility, making their inherent nutritional content available to plants when they need them.
Synthetic fertilizers are made to convey specific amounts of nutrients, at specific times, directly to plants, which are then absorbed and utilized. These seldom increase soil fertility, in the long term.
Unlike store-bought fertilizers (both organic and inorganic), compost and manure don’t contain any fillers intended to maintain a certain product consistency or shelf life. They are completely natural. Just what plants are looking for when seeking out nutrients.
Even better, if you happen to have a compost bin or any kind of livestock (chickens, cows, etc), this ‘gardening gold’ is free.
How Often Do Plants Need Nutrients?
Indoor and outdoor plants all need consistent access to nutrients during their active growth stages.
How often to apply those nutrients depends on a few factors, like what you’re using to supplement nutrients in your soil. The application method of store-bought fertilizers will dictate frequency, as well.
Compost – 2-3” of well-rotted compost should be worked into the top 6-8” of topsoil every year, prior to planting.
Manure – This has a higher application frequency, requiring top dressings around ornamentals, fruits, and vegetables every 2-3 weeks.
Inorganic liquids – One application every 7-14 days is needed to maintain a steady flow of nutrients.
Slow-release granules or spikes – these last anywhere from 2 months to an entire growing season, depending on the product.
How Long Does Fertilizer Last in Soil
How long fertilizer remains present in the soil will depend on certain environmental factors. Soil condition, weather, the types of plants you’re growing, and the application method and formulation of your chosen fertilizer will all be determinants.
Liquid fertilizer options only last a week or two, as most get absorbed by plants while the rest leeches away from roots.
Slow-release fertilizers can continue sporadically delivering nutrients for months.
Signs Plants Require Fertilizing
Being able to look at plants and determine if fertilizing is needed is a skill gardeners tend to naturally acquire over time
When plants are in nutrient distress, they usually need either nitrogen, phosphorus, or potassium. With visible signs showing in the foliage.
Foliage can’t photosynthesize on low nitrogen, causing fading color and wilting. Low phosphorus causes a reddish hue on foliage and low potassium will give the foliage a burnt appearance.
Importance of Soil pH in Fertilizing
Most plants, trees, and shrubs thrive in a pH range of 5.5 to 8.5. Hydrangeas, azaleas, and many berry varieties prefer a range of between 4.0 to 5.5.
Many popular ornamentals and shade lovers prefer it closer to the high end, while vegetables do very well somewhere in the middle.
Ph levels above a plant’s preferred range will block nutrients entirely. A lower level will leave plants vulnerable to heavy metals in the soil that inhibit photosynthesis.
Overfertilizing can alter pH levels, as well. For example, when too much phosphorus is introduced, soil pH levels can rise. Which, in turn, blocks phosphorus availability.
Soil pH Testing
DIY soil tests range from simple pH strips to those that detect specific nutrient deficiencies. Choosing the right soil testing kit and target results will save you time and money. Here are a few effective options to choose from:
Digital testing kits – test soil samples for current pH levels and amount of nitrogen, phosphorus, and potassium.
Analog testing kits – test soil for moisture content and pH levels, with some testing the quality of the light in specific locations.
Chemical testing kits – measure nitrogen, phosphorus, potassium, and soil pH.
Amending Soil pH
If your soil pH is too high, compost or manure additions will gradually and naturally lower soil pH over time. In a way that is most healthy for plants. After a few years, a soil test can determine if the pH is getting too low for plants to thrive in.
Some synthetic fertilizers are formulated with sulfur, aluminum sulfate, or lime to either raise or lower pH levels faster, as needed.
Verdict: Is Plant Food the Same as Fertilizer
The verdict is in, puzzle solved! We’ve seen some pretty clear examples of plant food vs fertilizer. They are two very different substances. One is made naturally, by plants, themselves, and the other is a processed formula designed to supplement nutrients in poor soil.
Plants produce glucose, starches, and carbohydrates through photosynthesis. This is when carbon dioxide in the air is absorbed by leaves and comes in contact with the chlorophyll cells that make our plants green. This also requires sunlight, water, and soil nutrients to function properly.
Macro and micronutrients form the building blocks of every plant that create the base from which every internal plant process stems. But, they can’t produce these vital nutrients. Instead, these are sought by plants via the soil in which they are planted. This is why we need to fertilize them.