If you have ever shopped for fertilizer for your plants, then you know the wide variety of options available. Water-soluble fertilizers are popular, often because they seem easy to work with: a scoop or so in the watering can and you’re done. Even within this subcategory, the options seem daunting: Organic? Synthetic? High phosphorus to promote blooms?
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To help clear these muddy waters, we tested five water-soluble fertilizers derived from a variety of sources. We applied them to plants grown for their fruit (‘Sun Gold’ tomato), flowers (a dwarf marigold mix), and foliage (‘Purple Ruffles’ basil). And while some of the results might be what you would expect, there were a few surprises.
Our control group of plants was grown with no fertilizer besides what was in the potting mix (Fafard 3B—a professional growing medium similar to many over-the-counter mixes) to see whether adding fertilizers made a difference in growth. The plants were planted in April, and we applied fertilizers every two weeks at the rates recommended for container plants on the packaging. In two cases, we did not follow the packaging instructions exactly as written. First, we applied Miracle-Gro Liquid All Purpose fertilizer at half of the recommended rate (this was an error caused by misreading the label and not the fault of the company); second, we used fish fertilizer every two weeks instead of every month as recommended on the packaging (this was done for the sake of consistent application across fertilizer types). All of these fertilizers were applied to three of each of the plant types tested. Average flower number and fruit number per plant were tracked for marigolds and tomatoes, respectively. At the end of the experiment, all plants were dried and weighed.
We tested a range of fertilizers that come from different sources: organic options, like seaweed and fish emulsion, to synthetics like Miracle-Gro. The NPK ratio is the percentage of the nitrogen, phosphorus, and potassium, respectively, that the fertilizers provide. All of these fertilizers are widely available, and the costs presented are from amazon.com.
All fertilizers offer a range of nutrients to plants, including nitrogen, phosphorus, potassium, calcium, zinc, and a host of other elements. Of these, nitrogen usually has the most effect on plant growth. Adding nitrogen usually results in more growth. This was evident in our study. The final average weights of the plants tested provided an obvious way to separate the influence of fertilizers on plants. As expected, plants grown without fertilizer were smaller than plants grown with fertilizer. Of the plants treated with fertilizer, those that offered the lowest percentage of nitrogen resulted in the smallest plants, while those with higher levels of nitrogen resulted in larger plants.
All of the plants grew reasonably well with no obvious nutrient deficiencies; however, some differences in plant growth emerged as the experiment continued.
One of the most interesting things that we saw was the earlier emergence and greater number of fruit on tomato plants that were not fertilized. Though interesting, this is not surprising because, unlike the fertilized plants, the plants given no fertilizer immediately devoted their energy to reproduction (fruit production) instead of vegetative growth (stem and leaf growth). Plants that were fertilized devoted their energy to growth and developed fruit later than the control plants. By the end of the experiment, they were clearly producing more fruit. The same general trend was seen with marigold flowers. With sufficient nutrients, plants prefer to grow before they reproduce, but if nutrients are limited, plants prefer to devote what resources they have to ensuring that there is another generation.
One of the most interesting things that we saw in this experiment was the failure of Miracle-Gro Bloom Booster to provide a consistent increase in average bloom number in marigolds or fruit number in tomatoes (which should be expected because blooms turn into fruit). At only one sampling date for marigolds did Bloom Booster have the highest average number of blooms. Bloom Booster is supposed to work by offering plants a high dose of phosphorus, an element that is supposed to improve the number of blooms. Phosphorus is certainly required for plants to bloom; however, only a small amount is needed. Adding more phosphorus can even be considered a waste of a natural resource because most phosphorus for fertilizers is mined from a limited number of sites around the world. With an analysis of 10–52–10, Bloom Booster offers a level of phosphorus that is excessive for most plants. Remember that any phosphorus added to your plant beyond what the plant uses could end up running down a gutter and into a local pond or lake. Once it’s there, it will undoubtedly feed algae and contribute to a damaging reduction of oxygen in the water, which could suffocate fish and other aquatic creatures. Though the use of a half rate of Miracle-Gro All Purpose fertilizer was an accident, it did show that, even when applied at less than the recommended concentration, fertilizers can still have a significant effect on growth. Though a little more fertilizer can improve plant growth, plants can still grow and be perfectly healthy with much less fertilizer than what is recommended.
Using fertilizer provides better results than not using fertilizer, and paying attention to the amount of nitrogen and phosphorus in the fertilizer you are using is important. What appears to be less important is whether the product is organic or synthetic as both types performed well in our tests. Based on our results, our recommendation would be to select a fertilizer with a low concentration of phosphorus relative to the amount of nitrogen, something like a 5:2 ratio, and to apply it according to label instructions—or even at a lower concentration.
Unlike granular, slow-release fertilizers, water-soluble fertilizers offer nutrients already dissolved in water, so they will be quickly available to plants.
There are so many different types of organic and synthetic fertilizers that dividing them along these lines isn’t a reasonable thing to do. That said, organic fertilizers are often (but not always) made from renewable resources, might be more likely to release nutrients slowly, and might be more likely to contain valuable micronutrients.
This can be an issue with any fertilizer. For most fertilizers, it’s important not to add them with every watering so that you can flush out any excess fertilizer. Be sure to follow the instructions on the label.
Water-soluble fertilizers will work fine for in-ground plants; however, some of the fertilizer is likely to run off during application. Granular fertilizers will release more slowly with soil moisture and are likely to be more efficient, unless you have a downpour right after they’re applied.
Jeff Gillman teaches horticulture at Central Piedmont Community College in Charlotte, North Carolina, where Mae Lin Plummer is a student.
Photos: Steve Aitken
To balance your growing media pH, select a water-soluble fertilizer that works with your irrigation water.
There are two primary goals to keep in mind when selecting a water-soluble fertilizer for your facility:
1. Maintaining the growing media pH within an acceptable range, and
2. Supplying your plants with a sufficient amount of essential nutrients for good growth and flowering.
The “best” fertilizer to use on your plants is the one that not only supplies nutrients, but also complements the alkalinity and nutrient content of your irrigation water.
When discussing how water-soluble fertilizer affects growing media pH, it is important to understand that water-soluble fertilizer cannot be applied without irrigation water. The best guide when selecting an appropriate water-soluble fertilizer is to balance the proportion of nitrogen in the ammoniacal form (acid) against the irrigation water alkalinity (base). Although other factors affect growing media pH, research has shown that it is the balance between the ammoniacal nitrogen in the fertilizer and water alkalinity that has the greatest effect on growing media pH of long-term crops.
To understand how the alkalinity concentration in the water and the percentage of ammoniacal nitrogen in the fertilizer interact, picture a balance with water alkalinity on one side pushing the pH up, and on the other side, with the ammoniacal nitrogen pushing the pH down.
If either of these factors is out of balance, the growing media pH will be affected. For example, using a fertilizer very high in ammoniacal nitrogen (like 21-7-7 acid) with low alkalinity water (like RO or rain water) is very effective at driving the growing media pH down, because there is nothing to neutralize all the acidic hydrogens (H+) being produced through nitrification or plant uptake.
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Applying the right water soluble fertilizers can work wonders on field crops, in home gardens, and even for houseplants. Just as the fruits, flowers, and vegetables you grow need adequate light and water to thrive, they need essential nutrients, too. Providing macronutrients and micronutrients that plants can quickly and easily access can help you net better results overall. Water soluble fertilizers can boost both crop growth and the quality of produce. In fact, which nutrients you provide—and how and when you provide them—can affect everything from the health and size of cut-flower blossoms to the thickness of your lawn and the taste of fruit and veggies.
To understand what water-soluble fertilizers are and how they work, you first need to understand how plants access nutrients. Plants acquire nitrogen, phosphorus, potassium, and other essential soil-based elements through their roots. But it isn’t until you fully water plants—or they get a good, soaking rain—that soil-based elements become accessible to your plants’ roots. Once watered, your plants’ roots draw in much-needed moisture and the nutrients present in the resulting soil solution.
Typically available in pellets or granules, water-insoluble fertilizers don’t readily dissolve in water. Instead, these “slow-release” dry fertilizers offer nutrients very gradually. Slow-release formulas are worked into the soil near the plants they’re intended to feed. When it rains or when you water your plants, some of the dry fertilizer’s nutrients reach your plants’ roots.
Unlike their slow-release counterparts, water soluble fertilizers easily dissolve in water and allow for the instant uptake of nutrients. Some water soluble fertilizers are commercially available as concentrated liquids. Others are dry preparations. To use, you measure out some of the concentrated liquid or the dry ingredients and mix with water. Then, you simply water with the quick-release fertilizer mixture. Because the included nutrients are already in solution, they’re immediately available to plants.
Of course, the nutrient sources in fertilizer products vary widely. Some ingredients come from natural, organic sources. Others come from artificial, inorganic sources. Although such chemical-based liquid fertilizers often contain higher percentages of essential nutrients, it’s possible to have too much of a good thing.
From a plant’s vantage point, nitrogen synthesized from a nitrate form like ammoniacal nitrogen or calcium nitrate is just as useful as nitrogen derived from natural ingredients like bat guano or blood meal. The same goes for a potassium-containing potash (which is produced from potassium chloride) and potassium derived from natural sources like sea kelp. Nevertheless it’s best to avoid chemical-based liquid fertilizers.
Synthesized from chemical salts, inorganic fertilizers can negatively impact soil health and structure. With their continued use, accumulating sodium residues contribute to higher acid pH levels. This, in turn, repels worms and other beneficial soil-dwellers and can “lock up” your plants’ ability to uptake nutrients. Excess fertilizer salts also draw water away from plant roots—the cause of fertilizer “burn” injuries. In container gardens, excess fertilizer salts can lead to scale formation on the outside of the pots or the top of the soil. Eventually, the soil’s capacity to retain water also declines. Excess nutrients, such as soluble phosphates, can leach into area waterways, contributing to algae blooms and other harmful environmental effects.
Liquid fertilizers derived from natural sources are better for plants and the soil. They generally have a low salt index, meaning they’re less likely to cause fertilizer burn injury, alter soil pH, or disrupt soil microbial activity. Because they’re derived form natural rather than inorganic ingredients, they may also be chloride-free and include bioactive extras like amino acids, enzymes, and beneficial bacteria. These work to feed and support the soil itself.
You can use water soluble fertilizers on new seedlings, in well-established gardens, and everywhere in between. Want to kick-start very young plants? Start with a relatively weak nutrient solution. Want to induce early flowering or early fruit formation? Incorporate phosphorus and micronutrients like zinc and manganese into the fertilizer you apply. As all of your plants grow larger, you can provide a stronger, all-purpose mixture every couple of weeks. Ditto for routine feedings of houseplants and container gardens.
Water soluble fertilizers have many benefits—and some drawbacks. Their uniformity of application is one of their biggest strengths. Plants take in dry, slow-release fertilizers only when water is present in the soil. Unless this fertilizer remains evenly distributed, you may end up with some nutrient-rich pockets and other nutrient-poor areas. Plants near heavier concentrations of fertilizer salts are at greater risk of burning.
Conversely, water soluble nutrients are immediately available to plants wherever they’ve been applied. They are fast-acting but also short-lived. As a result, water soluble fertilizers are less likely to injure your plants, but they must be reapplied more frequently. Also, some of these cost a little more than dry, slow-release products. Still, being able to deliver specific nutrients exactly where and when you want to just might be worth it.
You can tell how much of each of the “big three” essential nutrients a liquid fertilizer contains by checking its label for three numbers, separated by hyphens. This is known as the NPK ratio. (Nitrogen, phosphorus, and potassium are represented as N, P, and K, respectively.) Say a product label shows a ratio of 3-2-6. That means the product contains 3% nitrogen, 2% phosphorus, and 6% potassium by weight. Just what do nitrogen, phosphorus, and potassium do for plants?
Nitrogen (N)—important for green, leafy growth and new shoot development
Phosphorus (P)—stimulates blossoming and fruiting; aids in new root development and prompts root growth
Potassium (K)—essential for critical functions like plant rooting and cell wall formation
Other important nutrients include but aren’t limited to:
Calcium (Ca)—plant building block bolsters strength of cell wall; neutralizes certain plant acids; aids in protein manufacture
Magnesium (Mg)—important chlorophyll component; helps make plant fats, starches, and more
Zinc (Zn)—needed for chlorophyll production as well as certain plant enzymes and hormones; helps plants set seed
Boron (B)—regulates cell growth and metabolic processes
Molybdenum (Mo)—essential for plants’ nitrogen uptake and use; helps plants make proteins
If you want to learn more, please visit our website Lvwang Ecological Fertilizer.
Manganese (Mn)—another chlorophyll component; assists with uptake of other nutrients
Liquid fertilizers may contain different combinations of these additional elements. Check your product’s ingredients list for references to secondary nutrients, micronutrients, or trace elements.
You can buy organic water soluble fertilizers in either dry or liquid forms. Often available as a powder or in pellets, dry preparations are intended to be measured out, mixed with water, and then applied to plants. Similarly, the concentrated liquid formulas also require some measuring, dilution into water, and mixing before use. Depending on the age and size of your plants, you may want to adjust your fertilizer-to-water ratio. Carefully read the manufacturer’s recommendation on the product label before you mix. Some commonly used organic nutrient sources follow.
Liquid kelp and seaweed preparations can really pack a punch since they often contain some nitrogen, potassium, and many of the harder-to-find trace elements all in one place. Because it prompts roots to grow, some gardeners use very diluted liquid kelp/seaweed solutions as pre-germination seed soaks. Whether you’re growing cherries or cherry tomatoes, the nutrients found in most liquid kelp preparations also can improve the quality of the produce. When applied during fruit development stages, liquid kelp/seaweed may increase fruit size and boost sugar content.
Most fish-based fertilizers are derived from whole fish or fish parts which have been ground up and liquified. These products are usually richest in phosphorus and nitrogen and also may contain some trace elements, beneficial enzymes, and amino acids. Because they may be lacking, some manufacturers add extra sources of potassium to their fish-based preparations.
Although it’s possible to make your own fertilizer teas from finished compost or vermicompost, you won’t necessarily know which nutrients and microorganisms are in your DIY concoctions. Commercial manufacturers offer at least some specifics about the myriad ingredients in liquid compost/earthworm castings tea. These products often contain important trace elements, beneficial bacteria, and fungi which can improve soil structure and health.
Created from a mixture of different nutrient-rich ingredients, combination liquid fertilizers usually contain staples like fish or bone meal, animal manures, and seaweed or kelp extracts. Sometimes marketed as fertilizer supplements, there’s a combination liquid fertilizer for nearly every use case. For example, calcium deficiencies contribute to flower drop, fruit dropping, and tomato blossom end rot, and calcium-rich combination liquid fertilizers exist to mitigate (or, better still, to prevent!) these issues.
You can apply water soluble nutrients with a simple watering can or even an elaborate irrigation system. Want to use water soluble fertilizers with drip irrigation? Just be sure that your chosen fertilizer is thoroughly mixed first. (You might also want to strain it to remove any potentially clogging particulates.)
Besides directing liquid nutrients to your plants’ root zones, you can also apply them to plant leaves as a foliar spray. For this use, check your product label for foliar application instructions and dilute water soluble fertilizers accordingly. Then, decant your mixture into a clean spray bottle. Foliar feeding is particularly helpful if you need to take quick, corrective action. (To avoid burning your plants, lightly mist foliage when the ambient heat and humidity are low—early mornings or evenings are best.)
Water soluble fertilizers provide a greater degree of control in terms of the strength of the nutrient solution you provide and the frequency with which you provide it. What’s more, because organic water soluble fertilizers also contain many essential micronutrients and even beneficial microorganisms, they feed your plants and the soil. That puts you in a better position to combat common issues like insect pests, plant pathogens, and adverse weather events like record heat and drought. Best of all, no matter what you grow, you can choose liquid formulas containing combinations of essential nutrients to meet any special requirement of crops.
Ah, the memories of those science classes! Remember sitting there, soaking up knowledge about photosynthesis? It was like learning the ultimate life hack of the plant world – turning sunlight into food.
But wait, did your teacher delve into the world of fertilizers? You know, those nutrient boosters that often get mistaken for plant grub? The official definition is “any material, organic or inorganic, natural or synthetic, which supplies one or more of the chemical elements required for the plant growth.”
Okay, that’s a little formal. Simply put, fertilizer is not plant food (they make their food!); its plant nutrients – like sulfur, calcium, nitrogen, etc. – required for the plant to grow, develop, and reproduce. There are different sources of nutrients that plants can use. It’s sometimes hard to know what to apply since there are so many options. Let’s go a bit deeper.
Types of Fertilizer
There are two main types of fertilizers: organic and inorganic. Organic ones are naturally derived, meaning they aren’t man-made. Inorganic fertilizers, on the other hand, are the factory-made, water-soluble counterparts.
While both have their merits, it’s important not to overdo the use of either type. Applying too much, or applying them when plants aren’t actively growing, can spell trouble for both your plants and the environment. Think nutrient runoff wreaking havoc on water quality and contributing to pesky problems like algal blooms. 
Regardless of the type of fertilizer, they can do damage to plants and the environment. Luckily, the same basic principles of selection and application apply to both organic and inorganic, or synthetic, fertilizers.
In the wild, plants get their nutrients from natural cycles. In developed areas, we use fertilizers to mimic the nutrients these cycles provide to wild plants. Developed, in this instance, refers to lawns, landscapes, and potted plants or raised beds. Fertilizers should be applied when the essential nutrients for plant growth are depleted, which is common in “developed” situations.
Fertilizers are similar in concept to a nutrient cocktail that plants use to support their growth and survival. Think of it as their vitamin regimen. The main players in this nutrient mix are nitrogen, phosphorus, and potassium – the trio responsible for keeping plants thriving. These are often referred to a macro nutrient – not because they are the most important, but they are typically required in the highest amounts when compared to the micronutrients (think calcium, iron, sulfur, etc.). Nitrogen (N) beefs up those leafy greens, phosphorus (P) digs deep for root health and flowering, while potassium (K) is like a plant’s immune system booster. Some fertilizers also contain micronutrients to support plant growth as well. Match those numbers to your plant’s needs and voila!
The Impacts of Fertilizer
But before you go wild with the fertilizer, hold your gardening gloves! Timing is everything. Just like sticking to a skincare routine, plants need a fertilizing schedule to keep them glowing. Applying fertilizers appropriately will give you the best version of your garden. Overapplication is financially wasteful and can damage your plants. The extra nutrients get washed away and enter water sources, which directly impacts public health and aquatic ecosystems, and not in a good way.
Picture this: Florida, a sunshine paradise, plagued by issues like red-tide and blue-green algae. Sound familiar? Yep, blame it on eutrophication – the fallout from excess nutrients in the water, courtesy of nutrient runoff. When aquatic plants overgrow from the nutrients in the water due to fertilizers, oxygen levels plummet, leaving marine life gasping for breath. Hence the harmful algal blooms.
Fertilizers are regulated materials that contain plant nutrients. On the label, there must be a nutrient analysis. This analysis is the representation of the nutrients as a percentage of weight. These materials are listed on the nutrient analysis, as well as any additional nutrients. So, it is important to be able to read and understand the label to choose the right one. Let’s learn how:
Nutrient Analysis – you can identify this by looking for the 3 numbers on the label. These numbers give the percentage of the three main nutrients, nitrogen (N), phosphorus (P), and potassium (K), by weight. So, think N-P-K when you see these 3 numbers. For example, a 100lb bag has 12-3-4, this means that there are 12lbs of N, 3 lbs. of P, and 4 lbs. of K.
Guaranteed analysis: this is the analysis by weight of each element present in the fertilizer, warranted by the manufacturer.
Total Nitrogen: the total amount of nitrogen expressed as a percentage.
Additional Macro-nutrients: additional nutrients displayed as a percentage by weight of the total amount of fertilizer.
Additional Micro-nutrients: micronutrients displayed as percentage by weight of the total amount of fertilizer. In Florida, our sandy soil may tend to have low levels of micronutrients, but your soil content should be determined by a soil test. Excess amounts of these nutrients can damage and kill plants.
Nutrient Sources: details where the fertilizer was derived from.
How do you know which fertilizer to pick, you ask? Start with a soil test. It’s like giving your plants a doctor’s check-up.
You can easily take a soil sample at home with a kit, or that can be sent to the UF/IFAS soil laboratory, where inexpensive testing is available to the public. Or you can pick up an online based soil test kit at your local Extension Office. Either kit is simple, provides specific instructions, and provides recommendations based on the specific plant and situation you note on the form. Based on the results, choose a fertilizer that caters to the specific nutritional needs of your plants.
Choosing the right fertilizer depends on a lot of factors. The type of plant, soil, and time of year are just a few considerations. Lawn fertilizers would burn garden plants because they contain too much nitrogen and sometimes other chemicals that are meant to control weeds, so it is important to do your research and pick the best fertilizer for your type of plant. One size does not fit all when it comes to fertilizing your plants.
Complete fertilizers: this type of fertilizer contains all three of the primary macronutrients – nitrogen (N), phosphorous (P), and potassium (K).
A balanced fertilizer contains equal amounts of nitrogen, phosphate, and potassium – like a 10-10-10 fertilizer.
It may be beneficial to apply this type of fertilizer if your soil lacks all three nutrients, but if your soil is rich in 2, applying all 3 nutrients could burn your plants and lead to toxicity as well as waste your money!
Incomplete fertilizer: a fertilizer that lacks one or two of the three major plant nutrients.
Slow & Controlled release: provide nutrients to plants over an extended period of time. The idea is to save money by fertilizing less frequently and prevent excess nutrients from entering waterways.
Read the label to find the percentage of slow – or controlled-release nutrients in the fertilizer, paying particular attention to the higher amounts of slow-release nitrogen.
In Florida, any fertilizer that is labeled “slow-release” or “controlled-release” must contain at least 30% or more slow- or controlled-release nitrogen.
Organic fertilizer: made from materials that are derived from plants and animals, like manure.
Inorganic fertilizer: materials that are mined or synthesized from non-living materials.
Dry fertilizer: made of powder or granular materials that dissolve in water.
Water-soluble/liquid fertilizer: water soluble powders or liquid concentrates that mix with water to form a solution.
Check out Types of Fertilizer – Gardening Solutions – University of Florida for more information.
By understanding the delicate dance between photosynthesis and fertilization, you can be a gardening guru and Florida Friendly. Remember, photosynthesis is the plant’s superpower, while fertilizer is its trusty sidekick, ensuring a healthy and flourishing garden. So, next time you’re out amongst the blooms, armed with your watering can and fertilizer in hand, channel your inner botanist and let the gardening magic begin! Happy gardening, folks!
Are you interested in learning more about NPK Water Soluble Fertilizer? Contact us today to secure an expert consultation!