Growing bigger, stronger, & healthier plants

Have you ever wondered what fertilizer and soil supplements do for your soil? In this article, Mike "The Plant Man" Timm explains the ins and outs of the most commonly asked about soils and sold amendments.

Your Soil, Fertilizer, and Soil Supplements

As gardeners we have a general idea of what synthetic (man-made) fertilizer is, what’s in it, and what it does for our plants, but why do we use it?  They are mainly used as a quick fix to correct deficiencies of certain nutrients in the soil, normally being Nitrogen, Phosphorus, or Potassium.  There is a place for these in our gardening practices but should not be our first line of defense to plant health.  

Also, my suggestions and input here are based on the idea these plants are actually growing in the ground and not in containers.  Containerized plants almost always need to be supplemented with fertilizer.

You’ve probably heard me say in the past that healthy plants are the result of healthy soil.  This will never change.  My goal here is to help you understand soil better by informing you what it is made of, how our plants use it, and how to improve it naturally through the use of soil supplements. 

Components of soil. Soil is a mix of three basic ingredients; solids (e.g., minerals—those that make up sand, silt and clay) and organic matter, liquids (e.g., water), and gases (e.g., oxygen).  It’s the combination of these and in what proportions that make up soil.  Soil will also include living organisms such as beneficial bacteria, fungus and micro-organisms.  The combination of both gives you a living, healthy soil environment.  A healthy soil not only provides support for your plants but the proper nutrition they need.  This is a very basic definition of soil and how plants use it, but if you want to learn more, ask the experts at your local garden center.

Test your soil. Most soils are not well balanced.  This is why it’s important to have your soil tested.  It’s a great starting point.  It gives us an idea of the solids in your soil, including minerals and organic matter, along with its pH.  By correcting anything that is out of balance, we can normally improve the overall health of your soil.        

Most people look at the shelves full of supplements at their garden center with a glaze over their eyes, most likely thinking; what on earth are these for?  It can be intimidating, but these supplements are simply the minerals that may be lacking in your soil, and by adding these, will improve its health.  The addition of soil supplements is a long term solution to soil health and not a quick fix like synthetic fertilizers.  Let’s take a look at some specific supplements and what they can do to help your soil and your plants.

Discussed in this article:

  • Nitrogen
  • Phosphorus
  • Potassium
  • Magnesium/Calcium
  • Sulfur
  • Organic Matter/Compost


Nitrogen is responsible for plant growth, essential for photosynthesis, and aids in the uptake of water and other nutrients through the roots.  Besides Carbon, Hydrogen and Oxygen, it is the most prevalent element found in plants.  Therefore, it makes sense that this is the best place to start when talking about supplements, and possible lack of them, in soils.  Nitrogen deficiency can cause yellowing of foliage, poor growth, and even weak growth if found in too high of concentrations. 

There are many ways of adding nitrogen to your soil, including the use of compost and other organic matter, but the two main supplements I suggest are Dried Blood (Blood Meal), and Fish Emulsion or Seaweed/Kelp supplements.  As with any nitrogen fertilizer or supplement, too much can be a bad thing.  Again, I recommend a soil test if you think your plants are showing symptoms of decline.   

Dried Blood has been used for centuries.  It is formulated from cow’s blood and dried to a useable form, which breaks down to ammonia in the soil due to bacterial activity, which in turn becomes readily available to feed your plants.  Along with providing at least 12% nitrogen to your plants, it’s also a good source of other minerals, especially iron.  Some people have gone away from it because of fears that it may aid in the spread of Chronic Wasting Disease, but there is no proof out there that this is true.  Many people also use it as a rabbit repellent, but with mixed results; I guess it depends on your rabbits.  Both my father and grandfather used it as a repellent with good results, me on the other hand, not so much and have resorted to fencing.

If you really don’t want to use dried blood, for whatever reason, Fish and Seaweed/Kelp products, in dried or liquid forms, is another good option, especially when combined.  The reason I like to use them together is that Fish Emulsion has higher Nitrogen (12%) then seaweed/kelp products (1-2%), but the seaweed supplements have better potassium (2-3%).  They also provide other essential nutrients like Calcium, Magnesium, Sulfur, Chlorine and Sodium, and in combination again, are more complete.  These products are great supplements for vegetable gardens because of all that they have to offer.  They can be used as a soil supplement in solid form to help feed your plants and strengthen your soil or as a liquid fertilizer for direct feeding. 

Either one of these will work for you if you feel you are lacking nitrogen in your soil, but again, have your soil tested first to be on the safe side.


Phosphorus is responsible for flower & fruit production, and proper root development.  It also promotes beneficial soil bacteria and a healthy environment for earthworms.  But before adding phosphorus to any area I do recommend a soil test.  I’m sure you’ve noticed the absence of it in lawn fertilizers these days and the concerns of its effect on our waterways.  Wisconsin soils have fairly good levels of phosphorus and levels normally fall within recommended guidelines.   But like anything else, if land is overused, or it’s leached out because of years of heavy rains or watering, it can become an issue.  Also, it can get locked up in soil and therefore become hard for plants to use.  One more thing, if you’re soil pH is above 7 (like most of Southern Wisconsin); phosphorus supplements become less effective so an acidifying agent, like garden sulfur, should also be applied to help lower pH.  The introduction of mycorrhizal fungi (available in most garden centers) also aids in the breakdown and transition of phosphorus to plants roots.  There are numerous supplements on the market, but I would like to limit my discussion to the two I recommend the most.

First’ there is Bone Meal.  Its use dates back to biblical times when vineyard growers found out that their plants grew best on old battlefields, where old bones were buried.  Don’t worry, that’s not what Bone Meal is made with these days.  It is made mainly with crushed, steamed cow bones, making it very plant friendly.  Some people today have gone away from this, like Dried Blood, because false fears were spread that it may carry Mad Cow Disease, and again this is not true.  Bone Meal is still a great additive if your soil shows signs of deficiency and I not only recommend it, but use it myself. 

If you’re really not comfortable using Bone Meal, Rock Phosphate is the supplement for you.  It’s 100% pure mined phosphate rock, containing up to 32% total phosphorus.  Again being a natural element, it also contains other natural minerals such as boron, nickel and iodine which plants need in small amounts for optimum growth.  For best results, find one that is ground into a fine powder.  This allows for faster break down and quicker availability for your plants.  Rock phosphate is a very slow-release supplement so yearly applications are not necessary.  A little goes a long way; one application can last up to 5 to 10 years. 

So if your plants aren’t flowering of fruiting properly, this may be your solution, but again, don’t jump the gun; have your soil tested.

Potassium: Greensand - A Gardeners Secret Weapon

I’ve been a proponent of Greensand for a long time, and if you’ve ever talked to me about soil health, I’m pretty sure it has been part of the conversation.   So, what is Greensand?  It’s a naturally occurring mineral mined from ocean floor deposits from a rock known as ‘Glauconite’.  When crushed, it has a silica sand texture with a greenish color.  But it’s not really sand.  It’s an enriched mineral, one both your plants and soil will greatly embrace.  Think of it this way.  You now know the benefits of seaweed, and fish emulsion, as a supplement/fertilizer.  This rock has basically been absorbing these same minerals over time as they decay, and have packed them away in this sand-like substrate.

As far as nutrient makeup, it may not look like much on the bag with numbers around 0-0-0.1.  But remember these numbers represent what is available immediately to the plants, and greensand is something that breaks down slowly over time.  Although it doesn’t offer much for nitrogen, and contains smaller amounts of phosphorus, it does contain a good amount of potassium (6-7%), just not all available at once.  What it does have to offer besides the basics is other minerals and micro-nutrients, all of which are needed for exceptional plant growth and performance.  It contains Iron, Silicon, Magnesium, Aluminum, Sodium, Calcium, Titanium, Nickel, Copper and Hydrogen, along with over 30 others.  Think of it as a multi-vitamin for your plants and soil.

Greensand offers more than your plants daily nutrients, minerals and vitamins.  It also helps improve soil structure and its water holding capabilities.  It brings your soil to life by increasing microbial activity, and everybody knows a living soil is a plants best friend.  It will also help loosen clay soils as well as bind sandy ones.  It can absorb up to 10 times as much moisture then regular sand, which in turn, makes all of those beneficial nutrients and minerals more available to your plants.

All plants can benefit from the addition of Greensand, but superior results have been most noted in the growing of perennials, roses and vegetables.  It will make your perennials and roses healthier, more resistant to disease, and more productive with longer flowering periods.  In vegetable gardens, results have shown a significant improvement in plant growth, taste, color, nutritional value and overall health. 

Now that you have an understanding of what Greensand is, try adding it to a least some of your gardens this spring.  It truly is a secret weapon for us and you won’t be disappointed by the results.

Magnesium and Calcium

If you’ve decided to try Greensand you’ll be receiving a lot of the macro and micro-nutrients your plants and soil need to thrive, but of all these, Magnesium and Calcium are two I would like to discuss in a little more detail.  Why you might ask?  Both of these are essential, along with Potassium, and have important roles in the soil-plant relationship.  Again, start with a soil test.

Hopefully I have you convinced to try Greensand because it will cover both the Potassium and Calcium components involved. Throw in some Fish Emulsion and Seaweed/Kelp supplements and you’re really covered.  Ground egg shells or sea shells also make excellent sources of calcium.  Calcium is leached out of the soil very quickly, especially if you water a lot or we receive a lot of rain.  If you’ve ever experienced blossom-end rot on your tomatoes or peppers, it is caused by a Calcium deficiency.  This is why it’s important to keep an eye on Calcium, especially if you’re a vegetable gardener.

Magnesium is essential for photosynthesis, an activator for enzyme systems (allowing for proper nutrient break-down), promotes phosphate absorption, improves seed formation and germination, and promotes the synthesis of proteins needed for proper cell development.  Some call it the 5th major nutrient in plant growth.  Basically, it’s the element that allows everything else to work properly.  Epsom Salt (Magnesium Sulfate) is the most common supplement used today to supply Magnesium in home gardens.  The nice thing is that it also contains sulfur, which some consider to be the 4th most important nutrient.  There is a lot of information out there about the use of Epsom Salt and some disagree with its attributes.  There is much folklore out there about its use, and just like anything else, some is true and some is not.  In my studies I consider it something to continue to explore because I’ve gotten good results with it when I found it was needed.  Again, test your soil, although you may have to ask special for it because it’s not normally included in basic tests.  It’s important enough to ask for in my opinion if you are a vegetable gardener.  It can be low in vegetable gardens where heavy production is the goal.  We have a tendency to try to grow more produce then our poor little plot of land can sustain. 

In any case, keep an eye on these two.  You may never have a problem, but never rule them out if issues arise.  You can always talk to the experts at your local garden center for advice.


Sulfur has gotten a bad reputation in the past, especially before the Clean Air Act was implemented, for contributing to the acid rain problem, impacting our waterways.  It wasn’t the best for our health either.  Too much of anything is never good, balance is the key. 

There is a natural cycle of sulfur being released into the air by bacteria and plants and returned to the soil by rain.  In the past, the amount of Sulfur wasn’t an issue because of the over-abundance of it.  These days sulfur can sometimes be lacking in soils.  With this in mind, we need to remember Sulfur is important to our plants and some experts call it the fourth major nutrient after Nitrogen, Phosphorus, and Potassium.  It’s important in the formation of amino acids and proteins, is as essential in the formation of chlorophyll as Nitrogen, helps develop and activate certain vitamins needed by plants, and lowers the pH of soils making other nutrients easier to absorb. 

As always, start with a soil test.  In soils with a high pH, anything above 7.0, and low in organic matter, Sulfur is usually lacking.  These conditions are common around here.  I add some to my gardens every year.  The two supplements I recommend the most are Elemental Sulfur and Gypsum.

Elemental Sulfur is simply just that, Sulfur itself.  It is slow releasing and safe to use.  It normally comes in pelletized form and is easy to apply.  When applied, it is changed to sulfuric acid by microorganisms and becomes available to our plants.  It also lowers soil pH as well.  This is the form I use most often and you may wonder, why do I apply it every year?  Sulfur is mobile in the soil, not attaching itself permanently to anything for long, and therefore is susceptible to leaching.  With our snow melts and spring rains, Sulfur can disappear quickly; therefore, I apply it every year.  I do test my soil frequently to stay on track and in balance.

Another supplement that can be used is Gypsum, aka Calcium Sulfate.  I have used this in the past as well, but mainly on new gardens.  Why new gardens, you ask?  Not only is it a good source of Sulfur, and Calcium, it does a wonderful job of breaking up clay soils.  It takes a couple of years, but along with the addition of organic matter, turns a compacted clay soil into something workable and plant friendly.

Organic Matter/Compost

When we first started this journey on supplements we discussed that soil was made up of three basic components: solids (minerals and organic matter), liquids and gases.  We’ve covered the minerals, or nutrient supplements, needed for healthy soil and plants, but the other solid in the mix, organic matter, is just as crucial.  It’s the balance of all of these that create a healthy soil.  Therefore, I consider organic matter a supplement as well, and possibly one of the most important.  You can have all the other solids in balance, but if you have no organic matter, your soil will still basically be dead.

What is organic matter?  It’s simply decomposing plant matter such as leaves and needles, twigs or other large woody material, and any other living material, including animals.   The final material that results from this decomposition is called humus, or black gold, as us gardeners call it.  Another name for humus, or decaying organic matter, is compost.

What does compost do for our soils?  It stabilizes and holds it together helping to improve overall structure, supplies and stores nutrients for living microbes, works as a filtering system for pollutants (natural and man-made) which, in turn, helps decontaminate the soil, and feeds our plants, keeping them healthy.   

If you know me, whenever the question arises about what should be added to improve any garden soil, my first response is always the same; Compost, Compost, Compost!  This is especially true when it comes to vegetable gardens.  Did you know that the flavor you enjoy from your fruits and vegetables is directly related to the soil in which they are grown?  The better your soil, the better the overall flavor.  Not only does compost improve the flavor, it also helps increase the nutrient levels in the vegetables themselves. 

What are some of the other benefits?  It brings your soil to life, both below and above ground.  Below it provides an environment for beneficial bacteria, fungi, and other living things, like earthworms, which in turn brings your soil to life and creates healthy plants.  Above, these healthy plants attract other beneficial insects, such as pollinators and predators, and simply create the beauty and bounty that you first envisioned in your gardens.  In contrast, unhealthy plants simply attract bad insects and diseases to the garden, and this we don’t want. 

I hope this emphasizes how important compost is.  It should be put at the top of your spring to do list for improving your gardens.

Wrapping up…

Well, it’s been a long journey.  Hopefully you have a better understanding of soil supplements and will find them easier to use.  I hope I didn’t lose anyone because the use of these, instead of synthetic fertilizers, will not only greatly improve your soil and plants, but the overall environment as well.

Again, I’m not saying there isn’t a place for synthetic fertilizers in your overall program, but the less you can use the better.  Annual plants need extra fertilizer because they are such heavy feeders and they need fast, readily available nutrients at times to keep flowering.  Also anything grown in a container is prone to leaching because of the extra watering required, so they may need an extra boost.  They are a short term fix to a problem.  These fertilizers do nothing to improve your soil health and can actually be harmful if over used.  In fact, most of them are petroleum derivatives, they come from oil.  To name a few of the issues associated with them; they can leach quickly out of soils into our waterways, can kill the living microbes needed to bring soil to life, and can cause an increase in salts in your soil.

I hate to sound like a broken record, but before adding any of the supplements we discussed, except for the compost, a soil test is a must.  Once we find out what may be lacking or missing, we can work on a long term solution for your soil and plants, and not a short term fix. 

We talked about how we can improve your soil if any of the three major nutrients of Nitrogen (Blood Meal, Seaweed/Fish Formulas), Phosphorous (Bone Meal, Rock Phosphate), and Potassium (Greensand) are lacking.  We also discussed the roles of a few of the important minor nutrients like Calcium (Greensand, Gypsum, Egg Shells, Sea Shells, etc.), Magnesium (Epsom Salt), and Sulfur (Elemental Sulfur, Gypsum) as well.  We also talked about compost, which some call an amendment, but in a balanced form makes a great supplement as well.  When used properly, none of these are detrimental to the environment.  In fact, many are part of the environment.  We’re using what the Earth itself has supplied as a solution to our soil woes, without any major refining needed.

You hear a lot of talk these days about organic gardening, and many think it sounds overwhelming, but this is the direction you’re heading once you start using supplements.  By using these you’ve taken your first step.  I told you last time you might be surprised at what you might become, an organic gardener.  Doesn’t it feel good!  Happy Gardening!

Michael Timm
Ebert’s Greenhouse Village