Garden Fertilizer: How And What To Use For Feeding Plants

When it comes to houseplants, you constantly hear about the importance of fertilizing. It makes sense, considering the soil is isolated from the natural processes that normally refresh its quality.

But what about the soil in your garden? Even though Mother Nature does her best, the garden plants will still drain the soil of nutrients faster than they can be replaced.

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In Biblical times, they would let the land lie fallow every seven years to allow the ground to recover.

A more modern tactic is to practice crop rotation, which allows the soil to recover some essential nutrients at the cost of others.

But these methods aren’t always viable, especially if you’re growing perennials in your garden.

Let’s take a look at the complex world of garden fertilization and examine some different options as well as some tricks to get the best results. Read on to learn more about our fertilizing guide.

Garden Fertilizer: How And What To Use For Feeding Plants

Keeping your garden fertilized isn’t as easy as grabbing a random bag of fertilizer and treating the whole vegetable garden.

Different plants will need different diets, and understanding how fertilizers work can make a huge difference in the products you may decide to use.

Soil Nutrition 101

There are a lot of different factors that can affect soil quality, but nutrients and pH are among the most important.

The pH level of your soil can affect how well iron and other nutrients are absorbed, and some plants require more acidic soil than others.

This is important to know because some fertilizers will affect the soil pH.

Another important factor is the NPK rating on the package.

NPK stands for nitrogen, phosphorus, and potassium, respectively, and these are generally considered the three most important nutrients for your plants.

Nitrogen encourages foliage and stems healthy growth, as well as aiding photosynthesis.

Phosphorus is important for full, healthy blooms.

Potassium is essential for a plant’s immune system and stem strength.

You can get balanced fertilizer with an NPK, such as 5-5-5, or more of a specific nutrient, such as a high phosphorus 2-3-1.

The exact NPK ratio you’ll need will vary from one plant to another, so be sure to do some research before picking up a specific NPK.

But there are also additional key nutrients your plants need, such as:

  • Boron
  • Calcium
  • Copper
  • Iron
  • Magnesium
  • Manganese
  • Molybdenum
  • Sulfur
  • Zinc

Most of these will be present in fertilizer in trace amounts, but there are also soil amendments you can use to provide specific nutrients.

Granular Slow-Release Form vs. Soluble Liquid Form

Commercial fertilizers come in a wide range of options, and one of the most controversial options is which of the two types of fertilizer to use: slow-release or liquid-soluble.

There are a few brands out there, such as Osmocote, that address the key flaw in most slow-release fertilizers.

These brands use a special coating to regulate the release of nutrients, whereas most slow-release products will release their nutrients at different rates.

For example, nitrogen dissolves at a different rate than copper, so traditional slow-release fertilizers often need additional amendments to restore balance.

However, granular fertilizers are dry fertilizers that must be applied to the soil surface less often. They are often used at the beginning of the growing season on container-grown plants before switching to liquid-soluble options.

Meanwhile, liquid fertilizers must be applied more often, but the nutrients are available immediately upon application and are more easily absorbed by your plant.

They’re also quite popular because they can easily dilute to various strengths.

Water-soluble fertilizers are easily applied by dissolving in irrigation water and applying it to the soil around the plant and its leaves.

Although they are fast acting, they’re transient, meaning they must be applied frequently.

Chemical vs. Organic

Another consideration when purchasing commercial fertilizers is whether they’re organic or chemical.

Organic fertilizers are more easily processed by your plants but have a shorter shelf life. However, another upside to organic fertilizers is that it gives the plants a fertile foundation by building up the soil over time.

Chemical fertilizers usually have a longer lifespan but often come with an increased risk of causing burns to your plant if used improperly.

Additional Soil Amendments

Until now, we’ve discussed commercial fertilizers, but there are other products you might want to use at one point or another to improve your soil’s quality.

Here are a few of the more common ones and what they do, although this is hardly an exhaustive list.

Blood Meal and Bone Meal

These two products are exactly what they sound like: dried, powdered blood and powdered bone.

A blood meal is a great source of nitrogen, while a bone meal provides potassium.

These are often added as a dietary supplements for plants in addition to regular fertilizers.

Eggshell Tea

Made from boiling and steeping eggshells, eggshell tea is an excellent source of calcium carbonate (one of the most easily processed forms of calcium). It is technically a type of fertilizer, although its NPK is very low.

Epsom Salts

Those wonderful bath salts (Epsom salts) are a great source of phosphorus and are often used as an amendment for heavy bloomers.

Iron Sulfide

This is one of the most common treatments for plants with an iron deficiency.

It can also be used to make the soil more acidic in larger doses.


Agricultural lime is used to make the soil less acidic.

While not generally used to provide nutrition, it does contain calcium carbonate.

Organic Compost

Compost is not technically a fertilizer, but it can help restore your soil’s quality and nutritional content.

For the best results, it should be used in addition to fertilizer, not as a substitute.

Used Coffee Grounds

These are excellent nitrogen sources with a pH of around 6.5, making them an excellent choice for indoor plants and acid-loving plants.

They’re often used to sweeten the soil pH slightly while providing plenty of nitrogen and attracting earthworms.

Coffee grounds are best applied by sprinkling over the top layer of soil or diluting them in fresh water and drizzling them over the plants. 

Worm Castings

Despite the fancy name, this is literally just worm poop.

Worm castings are natural fertilizers with lots of nutritional value and are often used as an amendment for both soil and soil-free mixes.

Tips For Safely Fertilizing Plants

Finally, let’s look at some tips and tricks on how to use fertilizer effectively.

The very first trick is also one of the most important ones – testing your soil. 

This doesn’t need to be done yearly, and kits are readily available online.

A soil test will tell you the current pH level and level of nutrients of your soil, giving you a better idea of if or when you’ll need additional amendments and allowing you to adjust the NPK of your fertilizer to match the needs of your plant best. This will also help you know what you need to provide for healthier plants.

Second, always study fertilizer labels and carefully follow package instructions, as every brand differs slightly.

This can help prevent overfertilization and reduce the risk of chemical burns.

It’s best to lightly dampen the soil before applying fertilizer, as this improves absorption and also helps reduce the risk of damaging your vegetables and container plants.

When applying your chosen fertilizer, ensure to mix the fertilizer into at least the top 3″ inches of soil.

Moreover, remember to provide additional fertilizer if your crops and individual plants are growing in organic soils. 

 When using compost, pay attention to the needs of your common crops and indoor plants and apply accordingly.

Some will prefer it in the fall, while others should only be given compost in the spring.

If you’re planting or transplanting, blend the compost into your soil surface ahead of time so it can begin to do its job.

 If you plan to use any of the amendments we listed earlier, keep in mind that they are meant to supplement fertilizer, not replace it.

Products that amend a specific micronutrient should be used sparingly and always follow any packaging instructions or specific instructions for a particular plant.

For more general amendments, such as bone meal or worm castings, these can generally be used monthly, but you should still be careful not to upset the NPK ratio too much, or it will do more harm to the plant than good.

Finally, every plant has its own needs, so research each plant in your garden to get the exact NPK requirement and the frequency you’ll need to fertilize it.

This can be especially important as some garden plants are more prone to an iron or calcium deficiency and will need supplemental nutrition to be their best.

However, if you follow these simple tricks and choose a fertilizer that best suits your garden’s needs, you’ll get great results every year.

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