Wouldn’t it be great if you can just quickly choose the best liquid or granular fertilizer? Unfortunately, there are so many fertilizer types, elements, and factors to consider that choosing one can be rather, well… daunting.
Liquid and granular fertilizers have different pros and cons to consider in terms of (1) your goals and limitations, (2) what your plants need, (3) what the soil lacks, as well as (4) the fertilizer type and nutrition content you should use for best results.
Few of us who use fertilizers actually know the key advantages and disadvantages of granular and liquid fertilizers. Of course, we know common generalizations such as these:
|Liquid fertilizer||These act faster than solids, and can be spread faster over larger areas such as farms and orchards.|
|Dry fertilizer||Dry fertilizers such as powders, granules, pellets, and cakes are best for small gardens and farms because of lower cost, better control of nutrient release, easier storage, and control of wastage.|
|Gel fertilizer||Gel fertilizers combine the advantages of both dry and liquid fertilizers designed for slow or controlled nutrient feeding. They contain specific NPK macronutrients and chelated trace elements. They’re water-soluble and provide a high ratio of nutrients per liter.|
While mother nature doesn’t do labels, fertilizer manufacturers are required by law to inform buyers exactly what goes into their products. Thus, each package shows an NPK code: three numbers that indicate the proportion of elements in the fertilizer.
PRO TIP: When buying fertilizer from bulk sellers, write the NPK formula on your containers. And remember: that formula shows percentage by weight.
|Nitrogen (N)The first NPK number||Function: Nitrogen helps develop the parts of plants that you see above-ground, particularly the health of leaves.Deficiency: Your plant lacks nitrogen when the leaves are smaller than normal and many of the leaves are turning yellow.|
|Example 1||NPK 12.0.0: The fertilizer contains 12% nitrogen. NPK 0.1.1: The fertilizer has 0% nitrogen, 1% P, and 1% K.|
|Phosphorus (P)The second NPK number||Function: Phosphorus makes plants resistant to pests and diseases as well as helps in root growth and development.Deficiency: Phosphorus deficiency is not easy to spot. Some plants show purplish stems or dark blue-green leaves.|
|Example 2||NPK 1.9.1: The fertilizer has 1% N, 9% potash, and 1% K.NPK 7.8.9: A 100-pound bag of fertilizer has 7 pounds of nitrate, 8 pounds of phosphate (phosphorus), 9 pounds of potash (potassium), and 76 pounds of filler (also called ballast).|
|Potassium (K)The third NPK number||Function: Potassium helps plants to develop buds, flowers to blossom and fruits to grow.Deficiency: Potassium deficiency in plants show as chlorosis, or yellowing between the veins of leaves, scorching at the edges of leaves, and some plants show purple spots under the leaves.|
|Example 3||NPK 12.10.20 fertilizer for tomato plants: One kilo includes 120 grams N, 10 grams P, and 20 grams of potassium.NPK 10.10.10 or 5.5.5: This is a fertilizer that provides the same relative amount of nutrients, so which one you use doesn’t matter. What you must know is how much fertilizer you should use, and when.|
|Trace elements (not coded)||Minuscule quantities of calcium (Ca), sulphur (S), Iron (Fe), and magnesium (Mg) in the soil are secondary but are key elements for chlorophyll as well as for plant growth and development.|
PRO TIP: Other countries use NPKS where S stands for sulphur.
About 90% of fertilizers are dry. Powders, pellets, granules, or cakes are put into soil, but most are dissolved in water and then diluted before fertigation.
Whether organic or synthetic, dry fertilizer gives different benefits. Here’s a quick rundown of dry fertilizer forms.
|Cakes||DIY as well as commercial fertilizers cakes are made to be ground or powdered for dilution and control. Examples are dung cake, oil cake, neem cake, mustard cake, sugarcane cake, and fermented cake fertilizer.|
|Granules||Commercial grade fertilizer sold as concentrated dry granules are used for slow release. The granules are activated by water. PRO TIP: To prevent fertilizer burn, always wash away with water any granules left on leaves.|
|Manure||Animal feces, either raw or dried dung collected from animals have been used for centuries to fertilize crop soils. It can smell but is eco-friendly.|
|Mulch or compost||Organic fertilizer can be in the form of mulch (spread on topsoil) or compost (mixed into the soil) which is deteriorated bio-materials from plants or animals.|
|Pellets||Commercial as well as DIY fertilizers in concentrated pellets or chips are made for ease of application and for the slow release of nutrients. Examples are chicken manure, fecal sludge, wool pellets, goat pellets, and fish pellets.|
|Powders||Commercial and DIY fertilizer is made in concentrated powder form for ease of sprinkling or mixing into soil or compost, as well as for water solubility in hydroponic or indoor use. Many manufacturers of powder fertilizer use synthetics such as phosphorus, calcium, magnesium, potassium or silicon, or organics such as bone meal, fish, peat, neem seeds, or seaweed.|
|Sludge||Municipal sludge from community sewage can be collected, dried, treated, and ground into biosolid compost for ease of application as soil fertilizer.|
|Spikes, sticks, or stakes||Commercial fertilizers in spike forms are designed for hammering into the ground and for slow nutrient release over 6 months. Before using, know how much fertilizer to use, and the type of fertilizer for specific plants.|
PRO TIP: Hammer the spikes into soft, damp topsoil along the dripline for nutrient distribution and root contact when watered.
Since it’s clear that the wellbeing of our plants lie entirely in our hands, choose your fertilizer only after you have considered these common arguments for and against dry or granular fertilizers.
|Blending: Can be blended into specific types of fertilizer analysis.|
Application: Can be applied as broadcast or bands. With powders, there’s less chance of waste or spills.
Timing: Nutrients are available throughout the growing season
Cost: Cheaper when purchased in bulk. When ordering online, lighter weight means cheaper shipping.
Storage: Will not settle or salt out when stored for long periods.
Release control: Slow-release products (e.g., polymer-coated urea) available
|Non-liquidity: Requires water for nutrients and minerals to be absorbed by plants|
Non-distribution: Less mobile elements (e.g., phosphorus) stay in the individual granules until accessed by plant roots.
Rejection: Roots turn away from hot granules with too-high levels of potassium or nitrogen.
Inconsistency: Nutrition or mineral content of each granule varies and cannot be assured.
FACTOID: For centuries, food crops in China and in Japan grew on soil fertilized with human feces, the smell of which spread around agricultural provinces.
Liquid fertilizers can be natural concentrates or extracts, or they can be commercial products sold in agricultural stores as natural extracts, liquid concentrates, emulsions, or gels.
One advantage is that you can precisely control liquid fertilizers to provide a steady supply of nutrients. For instance, you can stop feeding dormant plants in winter or increase feeding for new growth.
The disadvantages? You need to a) remember to do it every time, b) never go away on long trips, and c) you can’t use them for slow release of nutrients.
- Liquid concentrates: Liquid fertilizers dissolve and mix with water more rapidly than powders or other dry forms and therefore work more effectively. These are best for hydroponic plants.
- Extracts or natural concentrates: Liquid fertilizer extracts are more concentrated by pressing, straining, and when most of the water content is removed, often by evaporation.
- Emulsions: Liquid fertilizers that come with A and B solutions are called emulsions. When the two solutions are combined, the nutrients and elements react with each other.
- Gels: Gel fertilizers such as liquid gel, starch gel, and seaweed gel combine the advantages of powder and liquid fertilizers. Slow-release fertilizers provide a high ratio of nitrogen, phosphorus, potassium, and other nutrients per liter of product (yes, they’re completely water-soluble).
|Urine||Anhydrous liquid ammonia||Fish emulsion fertilizer|
|Compost extract||Ammoniates||Hydrolyzed fish liquid|
|Grass extract||Aqueous ammonia||Water-in-oil emulsion fertilizer|
|Seaweed extract||Ammonium nitrate and urea||Pinolene polymer emulsion|
|Mulch extract||Nitrogenous fertilizers||Soluble calcium emulsion|
|Chicken manure extract||Potassium, phosphorus, nitrogen calcium blends||Ammonium nitrate emulsion, suspension, or gel|
|Aquarium water||Urea||Emulsifiable concentrates|
FACTOID: Colloidal clay and bentonite additives are used to prevent crystallization in liquid fertilizers during long storage.
Here’s a quick summary of the most common pros and cons of liquid fertilizers such as extracts, concentrates, emulsions, and gels.
Liquid Extract Fertilizer: Pros
Liquid Extract Fertilizer: Cons
Liquid Concentrate Fertilizer: Pros
Liquid Concentrate Fertilizer: Cons
Emulsion Fertilizer: Pros
Emulsion Fertilizer: Cons
Gel Fertilizer: Pros
Gel Fertilizer: Cons
PRO TIP: Emulsions are liquid fertilizers with A and B solutions. To fertilize, the two solutions must be combined
How long does it take for fertilizer to work? If quick-release fertilizer is used, plants absorb nutrients in 15 to 24 hours. If you use slow-release fertilizers, you’ll see the effects any time after three to 10 weeks.
How long do organic fertilizers last in the soil? Organic fertilizers need about two to six weeks to decompose but can nourish plants from three months up to 10 years. Nutrients in liquid fertilizers are immediately consumed by plants – the fertilizer remains in the soil for two weeks at most. On the other hand, dry or granular fertilizer remains active in soil from about six up to eight weeks.
Can I mix granular fertilizer with water? Yes. You should completely dissolve dry fertilizer in hot water (about 180° F).
Can I turn granular fertilizer into liquid? Yes. Soak 1 cup of granular organic fertilizer in one gallon of water for 24 hours, with occasional stirring. Strain out the solids. Use the liquid as fertilizer.
Why does granular fertilizer have more salt content? As a slow-release fertilizer, granular fertilizer is highly concentrated with nutrients that last longer. Higher salt content is due to high concentration. If this doesn’t work for your plants, switch to organic, natural, or diluted liquid fertilizer.
How do I know when I must fertilize? You have nutrient deficiency when you see generalized (not localized) symptoms of purple, reddish, or dying plant tissue (necrosis), stunted growth as well as:
- Dark green veins on pale green or yellow leaves (chlorosis) needs nitrogen;
- Dull, dark green or purplish leaves (interveinal chlorosis) towards the base means potassium is low;
- Reduced flowering means phosphorus is low;
- Rotting ends of blossoms means calcium is needed.
Note: Before applying fertilizer, check if it’s too much water that’s turning leaves yellow or pale green or if it’s the lack of water that results in dying or dead leaves
What NPK ratios are used for indoor herbs? Here’s a table of NPK ratios for indoor herb gardening.
Table 7: Recommended NPK for 10 Indoor Herbs
|Herbs||N (nitrogen)||P (phosphorus)||K (potassium)|
Which is better: foliar spray or soil fertigation? You can use liquid fertilizers either way. Here’s a summary of what you need to know.
|Foliar spray||Application: Can be sprayed on leaves|
Supplementation: Can supplement soil-applied nutrients
Timing: Can correct mid-season deficiencies
|Limitation: Rain, wind, heat, or pests limit effectiveness.|
Short availability: There is short-lived nutrient availability
|Soil fertigation||Application: Fertilizers is irrigated for ground absorption (via roots)|
Supplementation: Can supplement foliar-applied nutrients
|Escape: Nutrients can be carried away by water out of reach of plant roots.|
PRO TIP: Since nutrient intake is higher when absorbed via roots (compared to the foliar spray) always dilute organic liquid fertilizer before fertigation.
FREE PDF: Fertilizer Types and Calculating Application Rates (3 pages)
But, before you go, here are your key takeaways.
Because plants can’t tell us when they’re hungry or what they need to eat, it’s our job to know that and provide the right input.
Now you know: their lives are in our hands.
When choosing the better fertilizer, know what’s available and how to use it, what your plants need, and what the environmental effects will be. For example:
- Pellet VS liquid: Go for pelleted fertilizer if you buy in bulk for more savings and easier storage and handling. Pellet fertilizer releases nutrients gradually over the growing season. Use liquid fertilizer for quick absorption of nutrients to correct the severe nutritional deficiency.
- Fertilizer forms: Fertilizers can be gaseous (not available commercially), liquid (including concentrates, emulsions, and gels), as well as solid (including powders, pellets, sticks, and cakes). Solid fertilizers can be slow-release or fast-acting.
- Fertilizer content: Organic fertilizers improve the soil and provide a slower distribution of NPK nutrients and micronutrients. Synthetic or chemical fertilizers feed plants quickly with specific ratios of NPK nutrients. Unfortunately, the need for constant replenishment is bad for the soil and the environment.
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