It’s frustrating and perplexing when you apply fertilizer to your crop, yet they don’t flower or fruit as profusely as you had expected. So, you might wonder why the fertilizer isn’t working.
Your fertilizer isn’t working because you may have applied too much or too little of it or applied it at the wrong time. A fertilizer also becomes less effective in these instances:
- Wrong soil pH level
- Too much or too little watering
- Incorrect use of compost or slow-release fertilizer
It’s essential to strike the right balance between how much to apply and when to apply your fertilizer. You also must ensure that you create the right soil conditions for the fertilizer to be effective. Keep reading as I explain why fertilizers don’t work and what you can do to make them effective.
You’re Using Too Much Fertilizer for Your Plants
Too much of a good thing is not always good, and this goes for fertilizers as well.
While most plants need fertilizers to grow, thrive, and produce fruits and flowers, overfertilizing can damage plants and even cause them to die. Here’s how:
Excessive Use of Fertilizer Will Cause Root Burn
Overfertilizing causes soluble salts to accumulate in the soil. These salts burn the roots of the plants. Plants that suffer root burn fail to thrive, show stunted growth, and often do not flower.
The roots also take up these salts. The salts then travel to the leaves and burn the foliage.
This is very common when fertilizing a lawn. I’ve written an in-depth article about why fertilizer burns grass here.
Too Much Fertilizer May Attract More Pests
Overfertilizing can trigger greener and more lush growth. The dense foliage attracts aphids that feed on the leaves and weaken the plant.
Vigorous green growth also creates a dense canopy that prevents sunlight from reaching all corners of the plant. It tends to create a humid environment that attracts pests and fungus.
Overfertilizing Will Only Weaken Your Plants
As counterintuitive as it may sound, it’s true that overfertilizing can weaken plants.
According to a study conducted by the Washington State University, overfertilizing sunflowers produces weak stems that snap easily and fewer blooms.
According to the findings of a study by the University of Georgia Extension, overfertilization caused root burn in blueberry plants that showed up as scorched leaves and shoot diebacks.
You’re Using Too Little Fertilizer for Your Plants
Some plants like blueberries have lower nutrient demands than row crops and vegetables. Herbs, too, can grow in poor soil. They don’t need too much fertilizer.
However, plants like tomatoes and fruit trees are heavy feeders. They require fertilizers at regular intervals to promote bloom and set fruit. If you don’t fertilize regularly and in amounts needed by the plant, you might not obtain the harvest you expect.
You’re Using Compost Incorrectly
Although compost is an excellent fertilizer, it may sometimes fail to increase yield to desired levels. Here’s why using compost may not give you the results you expect:
Too Little Compost Won’t Provide Your Plants With Enough Nutrients
It’s not uncommon for farmers and gardeners to err on the side of less when using compost. However, pound for pound, compost contains fewer nutrients than conventional fertilizer. So, growers need to apply more compost than a conventional fertilizer to obtain an equivalent harvest.
Tip: I’ve written in-depth articles about why plants need nitrogen, phosphorus and potassium. Check them out!
Compost Alone May Not Be Suitable for High-Need Spaces
Compost is an excellent source of nutrients for plants and usually meets the nutrient needs of perennial beds.
However, compost alone doesn’t suffice for high-need spaces like vegetable beds or commercial farms and gardens where high turnovers are expected.
If you’ve been applying compost in these spaces and wondering why the harvests are meager, you probably need to supplement the feed with conventional fertilizer.
The Compost You’re Using Can’t Correct Nutritional Deficiencies in Plants
Compost takes a while to break down in the soil and become available to the plants. So, if a plant is exhibiting symptoms of a nutritional deficiency, you must use a synthetic fertilizer that the plants can use immediately and overcome the deficit.
Unfinished Compost May Compete With Your Plants for Nitrogen
Unfinished compost will continue breaking down in the soil and compete with the plants for nitrogen. This creates a nitrogen deficiency temporarily, during which plants may not receive the nutrients they need to grow.
You’re Not Using the Slow-Release Fertilizer Correctly
Slow-release fertilizers provide a steady supply of nutrients throughout a plant’s growing period. However, not applying it correctly reduces its effectiveness.
You must choose a slow-release fertilizer with the appropriate longevity. The fertilizer you apply should provide nutrients to the plant throughout its growing period.
If you choose a fertilizer that doesn’t last long, your crop won’t receive the nutrients it needs during the later stages of its growing period. Your crop won’t receive the nutrients it needs during the initial phases of its growth if you use a fertilizer that has a longer-acting period.
You should choose a slow-release fertilizer based on the length of the growing period of your crop. If you use a fertilizer with an extended acting period, dig it into the soil a few days before planting so that it breaks down and is ready to release nutrients when you plant your crop.
You’re Not Applying Fertilizer When Your Plants Need It
Plants benefit most from fertilization when growing actively and need the most nutrients. You must apply fertilizer during the following periods:
- The deciduous plants are leafing out.
- The plants are putting out new growth after being dormant during the winter.
- The plants are about to flower.
- Your plants are getting ready to set fruit.
- You need to correct a plant’s nutritional deficiency.
Fertilizing at other times when the plant doesn’t need nutrients or is dormant will not make it grow bigger or flower or fruit more.
Sometimes, fertilizing at the wrong time can harm your plants. You mustn’t fertilize in the following instances:
- Dry weather: Fertilizing drought-stressed plants stresses them further. The salts in synthetic fertilizers harm these weak plants. During dry conditions, you should let your plants rest. Or, you can use an organic, slow-release fertilizer.
- Winter: You don’t want to fertilize your plants when they’re dormant during winter. Fertilizing when plants are dormant induces them to put out new growth when they should ideally gather and conserve energy for a spring or summer burst.
- Before the last frost date: Late spring frosts aren’t uncommon in many parts of the world. Fertilizing induces plants to put out new growth, flowers, and fruit. A late freeze can damage the new growth and weaken the plant.
- Flooded soil: When the root zones of the plants are flooded, the fertilizer you apply will wash away.
You’re Not Using a Fertilizer That Suits Plant Needs
To thrive and grow, plants need a mix of:
These are called macronutrients.
However, as a grower, you don’t have to provide all macronutrients in equal amounts to your plants. Soils may be deficient or abundant in one or more macronutrients depending on the location, weather conditions in a region, and the types of crops being grown.
Nitrogen deficiency can show up as yellow leaf tissue between the green veins. The appearance of reddish, violet or reddish-violet patches on older growth may indicate phosphorus deficiency. However, if you don’t know what to look out for, a soil test is the best way to determine if your garden or farm soil is deficient in one or more nutrients.
A fertilizer is effective and can help a plant thrive if it can compensate for a deficiency. For instance, if the soil is deficient in phosphorus, a fertilizer with a nutrient profile of 3-15-0 (3% nitrogen and 15% phosphorus) will be more efficient than one with a nutrient profile of 4-3-3 (4% nitrogen, 3% phosphorus, and 3% potassium).
If the soil isn’t deficient in nutrients, you don’t need to apply any fertilizer.
You Didn’t Fix the Soil pH Levels Before Applying the Fertilizer
Most plants prefer a soil pH between 6.0 and 7.0, which is on the acidic side of neutral. Nutrients are more available to plants when the pH level is near neutral. So, your fertilizer may not work if you don’t correct for extreme acidity or alkalinity in the soil.
However, some plants love acidic soils. Blueberries and azaleas need an acidic soil with a pH between 4.5 and 5.2. These plants are heavy iron-feeders, and iron is available at low pH levels. You must ensure that the soil is sufficiently acidic for any fertilizer to work for these plants.
Add lime to increase pH in acidic soils. Use sulfur to lower pH in alkaline soils.
A soil test tells you if you have acidic or alkaline soil.
The SONKIR Soil pH Meter (available on Amazon.com) incorporates the Double-needle Detection technology that provides consistently accurate results. It’s an easy-to-use apparatus that needs no batteries to work. This pH meter also measures moisture levels in the soil.
Your Plants Are Getting Too Much or Too Little Water
Overwatering will wash away the fertilizer, so your plants are left with little to derive their food from.
On the other hand, watering too little makes the soil dry and hard. Any fertilizer you apply cannot penetrate the compacted soil and reach the roots of the plants. You need to keep this in mind when you apply fertilizer during spring.
Before applying fertilizer in spring:
- Ensure that the soil is loose, moist, and well-aerated.
- Break up large clumps.
- Water the ground to ensure it seeps in and doesn’t form a puddle on the surface.