A COMPLETE GUIDE TO FERTILIZER
The amount of information on the market about fertilizer in the garden can be truly dizzying, even for the seasoned green thumb! What do all of these numbers mean? Do I need synthetic or organic? Complete or incomplete? Liquid or granular? It makes it confusing to know precisely when you need fertilizer, which fertilizer to use, and when to use it. Check out this guide to simplify the decision-making process!
Why Do You Need to Fertilize Your Garden?
We fertilize our garden to encourage healthy plant growth by returning much-needed nutrients to the soil. Plants need nutrients to grow, just like people. When heavy feeders like tomatoes, asparagus, and cucumbers soak up all the nutrition in the soil, your soil becomes slightly nutrient deficient and thus needs replenishing. The soil in containers can become especially depleted, as nutrients can leach out of the pot, so always be sure to fertilize your container-planted veggies and flowers!
Understanding the NPK Ratio
Whether you use liquid fertilizer, granular fertilizer, or fertilizer spikes, they will always have an NPK ratio. NPK stands for nitrogen (N), phosphorus (P), and potassium (K). The numbers appear as a series of three numbers, indicating the balance of each nutrient in the fertilizer (i.e., 15-30-15, which has a 1-2-1 ratio of nitrogen, phosphorus, and potassium). An “all-purpose” fertilizer generally has a balanced ratio, such as 16-16-16, which contains 16% nitrogen, 16% phosphorus, and 16% potassium.
Complete vs. Incomplete Fertilizers
If the fertilizer you select has all three major nutrients, it is considered a complete fertilizer. So, for example, both of the ratios we shared above are complete fertilizers. On the other hand, if a product only supplies one of those major nutrients, it is considered an incomplete fertilizer. An example of an incomplete fertilizer ratio is 0-20-20, which has phosphorus and potassium, but no nitrogen.
While you might think it makes sense to use a complete fertilizer in every part of your garden, that is not always the case. Some soils will already contain enough of one or two of these essential nutrients.
Suppose your soil has sufficient potassium and phosphorus levels but low nitrogen levels. In that case, there is no point in adding more potassium or phosphorus into the soil. You can determine your unique soil needs by picking up an inexpensive soil test kit at your local garden center! The kit will tell you what nutrients are currently available in your soil and which are lacking.
Organic vs. Synthetic Fertilizers
Garden fertilizers derive from a few different sources. So, in addition to paying attention to and selecting the appropriate NPK ratio, you’ll have to decide between synthetic and organic fertilizers. What’s the difference? We’re glad you asked!
Synthetic Fertilizers
These fertilizers are chemically manufactured and typically composed of minerals, gasses, and inorganic waste materials. They are well known for being fast-acting and water-soluble. While they will give your plants an almost immediate boost, they need to be re-applied more often than organic fertilizers and used with caution; their water-soluble nature makes it easy for them to leach into waterways. They can also burn your plants if overused.
Organic Fertilizers
Organic fertilizers derive from natural, organic sources like organic waste and microbes. They improve soil structure, stimulate beneficial microorganisms in the soil, and won’t burn your plants when used correctly. They tend to have a lower NPK ratio and thus require a little more patience than synthetic fertilizers; while the results may take a little longer and be a little more subtle, the long-term effects of organic fertilizers are well worth it!
Liquid vs. Granular Fertilizer
The choice between liquid and granular fertilizer comes down to several factors. Granular fertilizers tend to be more cost-effective and more efficient for heavy applications. They also have a slow-release formula, which means that they will provide doses of nutrients at a slower rate for a more extended period of time. On the other hand, Liquid fertilizer tends to be a bit more expensive. It is fast-acting and easier to apply but usually needs to be re-applied throughout the growing season.
There is no overarching answer about what fertilizer to select and when to fertilize; it depends on your type of plants, current soil condition, and desired effect. When in doubt, pop into the nursery and chat with one of our experts! We will be able to help you select the right fertilizer for your Indianapolis garden.