Fertilizing a garden is one of the first tasks an indoor or outdoor gardener will learn to do. After all, it is the fertilizer that “feeds” the plants and helps keep everything in the garden growing healthy and quickly. For people new to gardening, the sheer number of fertilizers available and the different types of specialty additives can become overwhelming. One thing that might stand out at first glance is that fertilizers come in two forms: dry and liquid. Although these two forms are quite different, the basic purpose of both is the same: to provide nutrition to a garden or particular crop. Dry and liquid fertilizers each have their own advantages and disadvantages and a closer look at those advantages and disadvantages will help horticulturists decide which to use and when.
Commercially made fertilizers were originally only available to commercial farmers and horticulturists. Nowadays, there are many fertilizer companies that tailor to hobby growers as much as they cater to commercial growers. Many of the laws concerning the way fertilizers are distributed and packaged (labeled) were created when there were very few fertilizer manufacturers catering to hobby growers. This is one reason why much of the labeling and explanations of fertilizers can be confusing to hobbyists.
The N-P-K of a fertilizer is represented by three numbers on the fertilizer label. These numbers represent nitrogen, phosphorus and potassium, respectively. The N-P-K of a fertilizer tells the available percentages of those particular elements. It is important for gardeners to understand what these numbers represent but not to get too discouraged when they are comparing N-P-K numbers on the packaging of fertilizers. Both dry and liquid fertilizers will have the N-P-K percentages and “ingredients derived from” listed on the label. By law, fertilizer manufacturers must list these on the packaging of the product. This allows a gardener to compare the N-P-K of fertilizers to each other and also, possibly more importantly, to compare from what each fertilizer is derived.
Dry fertilizers, also referred to as granular fertilizers, are fertilizers that come in a dry form. The size and consistency of dry fertilizers can vary greatly depending on the brand and what the product is derived from. The physical consistency of dry fertilizers can vary from large grains the size of apple seeds to a very fine, powdered form. However, most dry fertilizers don’t go to these extremes but instead have a consistency similar to that of sand. Dry fertilizers are generally designed to be amended into the soil and release to the plants over time. This means the grower can mix the fertilizer into the soil (at the suggested rate) and the fertilizer will be available to the plants over a certain period of time. It is also common for dry fertilizers to be “top-dressed” onto the soil when crops are already in place. This is a way for dry fertilizers to be distributed to the plants if they need additional nutrition throughout their life cycles. Always be sure to check the manufacturer’s intended use and dosage instructions. There is a wide variety of dry fertilizers on the market. However, most dry fertilizers can be categorized as either an individual ingredient or a blend.
An individual ingredient dry fertilizer is a dry fertilizer that is derived from a single source. For example, bat guano is an individual ingredient that would be considered a dry fertilizer. Individual ingredients are labeled just like any other fertilizer with the N-P-K percentages listed on the packaging. Some growers like to purchase individual ingredients in order to create their own custom blends.
A lot of manufacturers have made it simple to purchase fertilizers for a specific purpose by creating blends of fertilizers. For example, to grow roses, a gardener may want to use a “rose blend” fertilizer. Blends are comprised of a mix of individual ingredients which are combined for a specific purpose. Many gardeners choose to use blends over individual ingredients because of the ease of use and the value of buying the ingredients premixed. There are a variety of specialty blends on the market suited for many different applications.
One other, relatively uncommon, type of dry fertilizer is a fully soluble granular fertilizer designed for hydroponics. These fertilizers are completely synthetic, soluble, and are usually quite expensive. Some of these fertilizers may even contain “self-buffers” to help maintain the pH level in the hydroponic system. Unless a gardener is growing his or her plants exclusively in hydroponic systems, these fertilizers are not necessary and are usually cost prohibitive.
One of the biggest advantages of a time-release dry fertilizer is it gives nutrition to the plants over an extended period of time. This is especially true when the dry fertilizer is mixed into the soil prior to planting. Although the initial amending of the soil can be tedious, a time-release fertilizer saves labor time in the long run. Another advantage of dry fertilizers is an extended shelf life. If kept out of moisture and intense light, most dry fertilizers will last close to forever.
Dry fertilizers offer less control to the grower. For example, if the plants are experiencing nutrient toxicity, it is impossible to remove nutrients after they have been mixed into the soil. If the soil is mixed improperly, the grower is sure to have problems from the very beginning. The point is dry fertilizers cannot be corrected as easily as liquid fertilizers. However, if properly applied at the manufacturer’s suggested rate, this is rarely an issue. Another disadvantage of some dry fertilizers is the amount of time it takes for the nutrients to become available to the plants. It takes some dry form fertilizers longer to break down which means it will take longer for the plants to start receiving the nutrients. Another disadvantage of dry fertilizers is they can be dusty and messy. It is always a good idea to wear a dust mask when dealing with dry fertilizers.
Liquid fertilizers are fertilizers that come in a liquid form, most commonly as a concentrate. In other words, the grower must dilute the liquid fertilizer in water before feeding it to the garden. Each fertilizer can have different concentrations so it is important to closely follow the manufacturer’s suggestions. As with dry fertilizers, the N-P-K percentages will appear on the fertilizer label along with the derived ingredients. Liquid fertilizers can be classified as either base fertilizers or special purpose fertilizers.
Liquid fertilizers that are designed to supply the basic nutritional needs to a crop are referred to as base fertilizers. Base fertilizers are usually categorized as either vegetative (grow) fertilizers or blooming (flower) fertilizers. The vegetative fertilizers are comprised of ingredients that are best suited for vegetative growth while the blooming fertilizers are comprised of ingredients that are best suited for flowering or blooming.
In addition to base fertilizers, there are many liquid special purpose fertilizers or additives. These can be derived from a single source or multiple sources and differ from base fertilizers in that they are not meant to supply the plants with their basic nutritional needs but instead provide some other benefit. For example, an enzyme formula designed to enhance root growth could be considered a specialty purpose fertilizer.
Perhaps the biggest advantage of liquid fertilizers is increased control. With a liquid fertilizer the gardener has control over dosage and how often the plants are being fed. Liquid fertilizers also give increased control when problems arise. The dilution rates and ratios between multiple liquid fertilizers can be quickly changed to reflect the growth of the garden. In other words, it is much easier to tailor a feeding program to the garden’s current stage of growth with a liquid fertilizer than with a dry fertilizer. Another advantage to liquid fertilizers is the instant availability of some nutrients. Many liquid fertilizers supply nutrients in a form that plants can readily use. This is advantageous because it allows growers to give the plants what they need at the exact time they need it.
Some liquid fertilizers tend to coagulate after sitting on the shelf for an extended period of time. Liquid fertilizers are also generally more expensive than dry fertilizers due to the extra processing and packaging.
In the end, a gardener must decide which fertilizer regiment is best for his or her garden. Just remember, there are no rules to experimentation in this realm. It is completely fine to experiment with both dry and liquid fertilizers until you have found the best fit for your plants or crop. You may even find that a combination of both dry and liquid fertilizers is the best way to supply your garden with nutrition. I know many growers who like to amend their soils with dry fertilizers and then use liquid fertilizers as needed as the plants mature. This allows the gardener to gain the advantages of both the dry fertilizers and the liquid fertilizers. When used correctly, dry or liquid fertilizers (or a combination) can produce the grower’s desired results. As with so many other aspects of the gardening hobby, the only way to know for sure which fertilization regiment is best for your garden is to experiment and try it out for yourself.
Eric Hopper resides in Michigan’s beautiful Upper Peninsula where he enjoys gardening and pursuing sustainability. He is a Garden & Greenhouse contributing editor and may be contacted at Ehop@GardenAndGreenhouse.net.