Liquid vs Granular (Dry) Organic Fertilizer – Which is Best?

You are looking for an organic fertilizer and trying to decide between liquid organic fertilizer and granular or dry organic fertilizer. Which is best? When should you use one or the other? Is one more organic than the other? Which one builds healthier soil?

There are many organic fertilizer options out there and in this post I’ll help you understand the choices.

Liquid vs Granular Fertilizer

In this post I will be talking about organic fertilizers unless I specifically say they are synthetic. I’ll also use the common definition for organic which does not necessarily mean it is certified organic.

A liquid fertilizer is any fertilizer that is sold as a liquid. Good examples include fish fertilizer, kelp fertilizer and extracted compost teas.

A granular fertilizer includes most solid forms, such as manure, compost, and all of the plant meals such as alfalfa meal. The term granular seems to be what people use for this but the word “dry” would be a better label. It is really only synthetic fertilizer that is sold in granules, but I will continue to use the popular term.

There are other types of organic fertilizer that are midway between these extremes. You can buy dry fish fertilizer that you dissolve in water before use. Even though it is dry, its properties are similar to a liquid fish fertilizer. Fish meal on the other hand is ground up fish and has properties like granular fertilizer. You can buy packaged manure to make manure tea. The resulting tea is a liquid fertilizer. The solid remaining after using the tea would be granular.

Why Use Organic Fertilizer?

There are three main reasons people use organic fertilizer instead of synthetic ones.

• They improve soil structure and health
• They provide a slow feed for plants
• A belief that organic is better

I’ll deal with the first two below.

As far as the third one goes there is very limited scientific evidence that organic fertilizer is any better than synthetic fertilizer for short term plant growth. Once the nutrients are in their ionic form, organic and synthetic are identical and plants can’t tell them apart. As far as providing nutrients to plants, organic is not better.

There are good environmental arguments for using organic material when the product is a waste product. It is certainly better to use waste fish scraps than making new synthetic chemicals.

There is also much talk about the non-nutrient chemicals in organic products and how these biostimulants benefit plants, including things like amino acids, cytokinins, auxins, vitamins, and humic acids. There is some evidence that these might help plants as a foliar spray but they are much less likely to work as a soil drench. For the most part, it is not clear which if any of these are beneficial.

Also important is that none of the organic fertilizers I looked at, provided a list of biostimulants in their product. Their marketing material may mention them in general terms but there is nothing on their label.

If they were really critical to the product, don’t you think companies would list them as important ingredients and provide a minimum concentration value for them? For all we know these products might only contain microscopic amounts which will have no effect in soil.

The Humus in Organic Fertilizer

We talk about compost as being “finished”, as if the decomposition process was complete. This is far from the truth. To our eyes it looks black and we no longer see the banana peel or apple core, but most of that organic material is still undecomposed. So-called finished compost is mostly large organic molecules and it has a long way to go before it is fully decomposed. A rough number is 3-5 years in the garden.

This material is commonly called humus, although humus does not really exist. This humusy material is the main reason for using organic fertilizer.

Does Organic Fertilizer Improve Soil Structure?

If I said yes, most of you would agree. After all, this is one of the main benefits of organic fertilizer.

The correct answer is, maybe!

As the humus enters the soil, it provides a home for microbes which continue the decomposition process. It also holds moisture making it easier for plants to grow and it has chelating properties that allow it to hold nutrients. Over time the humus and soil get mixed together and the aggregate structure of the soil gets better.

As aggregation increases, soil becomes more fertile, holds more air, reduces compaction and the soil becomes more friable – that crumby characteristic gardeners all dream about.

Here is the important point. It is the humus-like material that causes all of this. It is NOT the fact that the fertilizer is organic.

This critical fact has been mostly lost in discussions. It is certainly lost in the marketing material of many organic products. Gardeners associate organic with soil building, but the two are not necessarily related.

Granular fertilizer contains lots of large organic molecules that end up forming humus. Think of bulky material like manure, compost and a pile of leaves. That “bulk” is what makes humus. Without it there is no humus.

Consider a big pile of fish guts resulting from the fish processing industry; correctly termed gurry. It certainly has bulk and if it is composted, it will form humus and be just as good as any solid fertilizer for building soil health. But that is not what companies do. They take that bulk and treat it with enzymes to quickly decompose the organic matter to release nutrients. Or in a worse case, they harvest live fish, remove most of the solid material and use the drained liquid to make fertilizer.

The end product is a liquid that certainly contains organic molecules along with ionic nutrients, but there is little if any bulk remaining. There is no humus to add to the soil. For this reason, these liquid fertilizers do almost nothing to build healthier soil and they don’t increase the organic level in soil to any significant amount.

Seaweed meals – the dry ground up seaweed – when applied to the ground, in large quantities, will improve soil. Liquid seaweed extracts have most of the bulk organic material removed and don’t improve soil.

Granular organic fertilizer builds soil structure, liquid does not.

How Do We Know Liquid Fertilizer Doesn’t Contain Humus?

Have a look at liquid fertilizer claims. None claim to contain humus even though it is well known that humus is good for soil.

Looking at the Neptune fish fertilizer label you can see that 75% of the nitrogen is in a soluble form, indicating it is not tied up in large molecules. On the other hand the soluble nitrogen in granular fertilizer is usually below 10%.

Organic material like humus, manure, compost and even banana peels are not soluble in water. You can use a blender and make a smoothy out of them, but that still contains a lot of bulk. If you pour the smoothy through a coffee filter you will get most of your banana back.

The most telling evidence is the speed at which nutrients are released once applied to soil.

Humic Acid Liquid Fertilizer

So humus is good, but what about humic acid, a component of humus?

Don’t be fooled by these products. They have nothing to do with the humus discussed above, and there is evidence humic acid does not exist in soil. One product I looked at claimed it was 100% soluble – that means it contains no humus.

Many brands don’t even tell you how much humic acid is in the product, but they make all kinds of claims for it.

Does Organic Fertilizer Provide a Slow Feed for Plants?

By now I am sure you have guessed the answer? Maybe!

One of the key benefits of organic fertilizer, compared to synthetic, is that organic is a slow feed. Instead of providing all the nutrient at one time, they are provided slowly over months and even years. As compost continues to decompose it provides a slow release of nutrients for 3 years, and that is good for plants.

The reason for this slow release is that most nutrients are tied up in large molecules and it takes time for microbes to release them. That bulk I talked about is full of nutrients, just waiting to get out.

The humus in granular organic fertilizer provides a slow release of nutrients.

In liquid fertilizer, there is very little humus and as a result they release their nutrients quickly. How quick? The Neptune fish fertilizer suggests fertilizing every two weeks. KelpGrow, a liquid kelp fertilizer should be applied “monthly or every two weeks“. These are common recommendations for liquid fertilizers.

Liquid fertilizer is a quick feed.

One of the arguments organic growers make agaisnt synthetic fertilizer is that it is a quick feed, which it is. It is odd to me that those same organic growers praise liquid fertilizer and never complain about the quick feed!

Is Liquid Fertilizer an Eco-friendly Option?

Liquid fertilizer does not build soil health and is not a slow feed and these are the two main reasons for using an organic product. A possible benefit is that they recycle waste products.

But that is not always true.

Many manufacturers of fish fertilizer make their product from emulsion which is made from live harvested fish. They are taking feeder fish from the ocean, reducing a food source for larger fish, so that we can feed it to our plants. It is also used in pet food. That is not an eco-friendly option.

Other companies use fish scraps and some use invasive fish like carp. That is certainly greener. Neptune does use fish scraps that would normally go to landfill – if you want a fish fertilizer, consider them.

Kelp is now farmed and some companies use this as their source. Other companies use seaweed that has washed up on shore. Both are green options. But in the northeastern US, they use native living seaweed and there are concerns that it is being over-harvested. Don’t buy kelp products unless you know they are harvested sustainably.

More Disposable Bottles

Liquid fertilizer is 98% water. That means it has the same environmental concerns as using plastic water bottles. We are shipping a lot of water around the globe in plastic bottles.

If you like the idea of using fish and seaweed, consider using the dry meals instead of the liquids – they use much smaller containers.

Consider this. To get the same amount of nitrogen, you can buy one pound of urea fertilizer, or 46 pounds of a liquid fertilizer (N=1%). Shipping is a huge environmental problem.

Is liquid Fertilizer Green?

Liquid fertilizer may be organic, but it is difficult to see how one can claim it is a green option. In some cases you might even be able to argue that synthetic fertilizer is greener than organic liquid fertilizer.