How to Fertilize the Soil for a Vegetable Garden

Last Updated on August 18, 2021 by Kimberly Crawford

Your vegetable garden may be yielding pretty satisfactory results, but that doesn’t mean you don’t need to use fertilizer. In fact, it may be that whatever yield your plants are putting out is not the best they can do; so, you need to fertilize them properly.

Think of fertilizers as the nutritional supplements your plants need to achieve their full potential.

The soil also has its naturally occurring nutrients that plants take up. And if you’ve been growing plants in your garden for a couple of years, they’ve probably used up a significant portion of these nutrients.

Therefore, you need to replace these lost nutrients before growing new plants to maintain the optimum level for healthy growth. This is typically done using fertilizers (organic or inorganic).

Related: Garden Fertilizers Broken Down: What Does “N P K” have to do with Gardening?

fertilizing soil for vegetable garden

Types of fertilizers

When looking to fertilize your vegetable garden, you can either use organic fertilizers or inorganic (synthetic/processed) fertilizers.

Inorganic/synthetic fertilizers

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These are manufactured from natural ingredients like potassium chloride (KCL), phosphate rock (P), and sodium chloride (NaCl) salts. They are quick-release, i.e., they deliver nutrients to plants almost immediately after application.

Synthetic fertilizers usually have three numbers printed on the container/bag, such as 10-20-10. These numbers indicate the percentage of major nutrients in the fertilizer; the first number represents Nitrogen (in this case 10 percent), the second number Phosphorus (20 percent) and the third number potassium (10 percent).

The remaining percentage (60% in this case) is a mixture of inert filler and other nutrients. Illinois soils typically have good trace/minor elements count, and thus, just paying attention to these three nutrients when choosing a fertilizer will do little harm.

Related: Ultimate Guide To Summer Fertilizer

Organic Fertilizers

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Organic fertilizers are obtained from plant and animal matter. Unlike synthetic fertilizers, organic fertilizers are not quick-release. Instead, they must first be broken down by microorganisms in the soil before they’re available to plants, and this takes some time. Examples include animal manure, kelp, fish emulsion, dried blood, and bone meal.

Organic fertilizers are also bulkier and contain lower nutrient percentages than synthetic fertilizers. Therefore, you will often have to mix different types to ensure that you give your soil balanced nutrient content.

The slow-release nature of organic fertilizers comes with some benefits. First, nutrients are released in a controlled, digestible, and safer manner to your garden plants; the risk of overdose is minimal to non-existent. Second, you do not have to apply organic fertilizer as often since it stays longer in the soil.

Animal and plant matter also raises the level of organic matter in the soil and thus, improves its texture. 

On the flip side, organic fertilizers are more expensive upfront than synthetic fertilizers but can be quite economical for small gardens in the long run.

Test Your Soil

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If it’s your first time gardening in your present location, you must first have your soil tested before buying and applying fertilizer. Soil testing indicates the levels and availability of nutrients in your soil and recommends which nutrients to add. It’s often free or low-cost and should be performed every two years.

Start by marking eight well-scattered spots across your garden. From these spots, dig 4 to 6 inches below ground, collect small amounts of soil, mix them, and dry them at room temperature. Now take ½ pint of soil from the sample, wrap it well, and send it to the nearest soil testing laboratory or your local cooperative extension.

After analysis, the lab will send you the test results alongside lime and fertilizer recommendations for your garden soil. If you are still unsure on how to proceed, you can contact one of your local landscapers and give them the test results for recommendations.

Fertilize your Vegetable Garden Soil

Once you have the test results, you can now fertilize your garden soil. Fertilizing is usually a two-stage process that will first be performed before planting and then midway through the growing season.

Broadcast fertilizing (To start your garden)

This technique is applied when preparing your garden for spring planting. You should use a complete fertilizer, i.e., one with the three main nutrients of Nitrogen (N), Phosphorus (P), and Potassium (K), and make sure to apply it evenly according to the soil test recommendations.

Broadcast fertilizing will provide your vegetables with the nutrients needed to see your vegetables through their first period of growth. Phosphorus is important for seedlings’ root development and growth, while Potassium strengthens their ability to resist diseases.

Note that of the three essential nutrients, the Nitrogen composition should be the lowest. This is because nitrogen encourages leafy growth, and too much of it when starting your garden delays maturity, reduces flowering, and reduces yields. Vegetable crops need nitrogen the most later on when they begin to fruit.

Side dressing (Later in the Season)

Halfway through the growing season, your plants will have used up most of the nutrients from broadcast fertilizing. Therefore, side dressing is performed to replenish essential nutrients for plants to use for the remainder of the growing season.

Depending on the vegetables, the demand for nitrogen at this point may exceed that supplied by broadcast fertilizing, and thus, a nitrogen side-dressing may be needed.

Side dressing increases the yield of vegetables and should be performed for leafy crops, root crops, and greens when they’re half grown. For beans, cucumbers, tomatoes, sweet corn, and other similar plants, it should be performed when the plants begin to set fruit.

Use a hoe to make a four-inch deep trench along one side of the row. Apply your fertilizer in the trench and cover it using the soil you removed. You are advised to use ½ cup of fertilizer around each plant and ensure that the garden is well watered after fertilizing.

Safety Precautions

  • When not using your chemical fertilizers, make sure to store them properly in a garage or shed. 
  • When using/storing fertilizer, follow the instructions printed on the package to prevent environmental damage or personal injury. 
  • Avoid overuse as excess chemical fertilizers will harm your vegetables rather than make them grow better. It may also wash away into water sources or leach into the ground, leading to pollution.