Amending Your Soil
By Amanda Kanehl, Vegetable Production Manager
March 1, 2024
Having a robust, resilient, and healthy garden doesn’t start with the plants- it starts with the soil. When your soil and the life within it is thriving, all life benefits. Landscapes, gardens, farms and fields all should focus on soil health.
Thankfully in Iowa we are blessed with rich, black gold for soil due to the prairies that used to call our state home. However, even our coveted soils can deteriorate. This deterioration can lead to problems like erosion, compaction, poor crop growth, and die off of the microfauna that live within it. On a large scale these problems have impacts like flooding, landslides, low yields and crop die off, and so on and so on.
Many home owners are left with little to no topsoil after housing development, and have to put in considerable work to begin growing the ideal soil composition around them, or hauling it in. While there is no easy fix for having poor topsoil, recharging what you do have is doable and important.
Be warned, soil science is real, and it is important to grasp the general concepts of it when amending your soils. This article includes a “minimal work” section, just in case you are just looking for an easy fix as your first steps, and gets progressively more in depth:
· Minimal Work
o Compost cure-all
o Containers
· Soil Composition
o Balance is Best
o Nutrients and pH
o Microbiome
· Testing your Soil
· Amendments
o Nutrients
o Organic Matter
o Microbiome
· Incorporation
· Up-Keep
o Avoid Chemicals
o Rotations
o Compost
o Testing
Minimal Work
Compost: The Cure- All
The easiest and most reliable quick fix for any soil is going to be compost. Compost is an excellent source of organic matter, nutrients, and microorganisms. When it is incorporated it starts decomposing and blending into the surrounding soil fairly quickly. If you are in a pinch and need to plant straight away in your soil, add up to 50% well matured compost.
Containers
An even easier way to plant in a pinch, is to use containers. These can be as simple as 5-gallon buckets with holes in the bottom or elaborate as raised beds. Either way, a media is bought and used instead of soil in most cases. Most medias are primarily composted on peatmoss with perlite and added minerals. These are sterile, weed free, and have the ideal composition, making them an easy and complete way to grow.
Soil Composition
Balance is Best
Soil provides four major things for plant growth: Anchorage, nutrients, water, and air. An ideal soil is composed of
· 45% minerals
· 25% Air
· 25% water
· 5% organic matter as well as
· Equal amounts of sand, silt, and clay. In a perfect world all soils would be this “loam” type, but usually it takes elbow grease and additions to get close to it.
When these components are dramatically out of balance it can cause major issues
· Poor water retention
· Nutrient leaching and low storage
· Drainage and percolation
· Root growth
Adding organic matter can help retain water and nutrients. Adding sand can help with drainage and gas exchange. Adding clay helps with nutrient retention and anchorage. On the other hand, too much sand will lead to pour nutrition and thirsty plants, and too much clay will lead to compaction and slow percolation of water, or flooding. It all needs to be balanced in order for soils be suitable for life.
For this reason, premade soils and medias are handy for quick fixes in small areas. Not only do they usually contain a balanced mix of all of these, they are sterile and relatively weed seed free. You can buy enough to amend a large plot, but it can get very expensive.
To save money and be more precise, use the ribbon test to determine what your soil type is. This simple home test will give you an approximate percentage of sand, silt, and clay which you can use to determine if you need to add any of them to your soils.
Nutrients and pH
The nutrients in your soil are just as important as its composition. When your soils are not nutritionally balanced it can cause deficiencies and toxicity issues. And if the pH of your soil is not within a certain range, your plants may not be able to take up those nutrients.
There are two sets of nutrients that plants need to grow properly: Macro and Micronutrients. Macronutrients are what compose most of the plant’s tissues, and therefore are highly essential
· Carbon
· Hydrogen
· Oxygen
· Nitrogen
· Phosphorous
· Sulfur
· Calcium
· Magnesium
While Carbon, Hydrogen, and Oxygen are taken up via the air and water, the others come from minerals in your soil.
Micronutrients, also known as trace elements are just as important for plant growth and cell function. They are
· Iron
· Manganese
· Copper
· Zinc
· Boron
· Chloride
· Molybdenum
Other elements, nickel, cobalt, and silicon are also needed but are usually not listed on labels or provided. Micronutrients are usually found in healthy amounts in soils, but should be still be tested for.
pH Scale
pH (potential of hydrogen): scale of 1-14
1 being acidic
7 neutral
14 alkaline
Most plants do well with soils between 6.5 and 7 pH. Nutrients are available in different amounts based on the pH of a soil. In an acidic soil, many micronutrients are readily available for uptake, but macro nutrients are not, while in alkaline soils only certain few nutrients are available in general.
To increase pH, lime and calcium-based products are used. In Iowa, our soils are limestone based, which mean they run on the alkaline or high side of the scale, so you will most likely need to lower your gardens.
To lower pH, use sulfur-based products. Aluminum sulfate gives the fastest results, but it can be toxic to plants in large quantities, so elemental sulfur is recommended. Over time, adding organic matter such as pine needles and peat moss will help lower pH levels. Organic matter that is acidic is broken down by bacteria and converted into sulfuric acid over time, which lowers pH.
Microbiome
Even with the perfect composition, nutrients, and pH, a soil would just be dirt without the tiny ecosystem within it. From the insects, to the worms, to the fungi, all the way down to the bacteria- they all have a part to play in the growth and health of soils. While most of these critters are already in place, helping them thrive will ensure your soil is resilient and provide for your plants for years to come. Compost is the best way to acquire this ecosystem. Consider getting a microbial inoculant to get an ecosystem going, and adding some worms while you’re at it.
Testing Your Soil
You finished the big science part! Good for you! Now how do you test for all these variables? I would recommend sending them into a lab. All farmers get their soils tested, and you are no different. We use Midwest Laboratories here at our farm, but you can try others like the University of Minnesota, Michigan State, or the University of Wisconsin. They can test for all nutrients, pH, and organic matter content. They may also be able to recommend what can be done to increase your soil health. When starting out, I recommend an in-depth test with any extra help from the labs you can add on to really get to know your soil.
Taking soil samples should be done in the way your lab recommends, but as a general rule, you want a good representation of the entire plot. I take random samples from different locations and depths. For small areas, I will mix them together to represent the whole plot, but from large ones I will test multiple and specific locations. If you test separate areas, be sure to label them in a way that makes them easy to keep track of when your tests do come in.
There are also kits you can buy to do the tests yourself if you loved all that science and want to dive deeper and get your hands even dirtier, but be prepared to do more and more research as you go.
Amendments
Nutrients
If you are seriously lacking specific nutrients, you should look for specific products to amend your soil.
· Potassium- Potash
· Phosphorous- Bone meal
· Calcium- Lime
If you simply are a little low in your nutrients in general consider adding a complete fertilizer or simply adding compost.
A little goes a long way when it comes to fertilizers. With compost and other solid forms of amendments, nutrients are both readily taken up and made available over time when bacteria break them down. You can buy these nutrient amendments in liquid, granular, or more solid forms.
Organic Matter
More natural forms of fertilizer also add organic matter to your soils. Compost is a wonderful addition to your garden every year, but it can be high in nutrients which can be detrimental to your plant’s overall health. They tend to have more fragile growth and be more susceptible to pests and diseases when given an excessive amount of nutrients.
Consider adding things like leaves, lawn trimmings, straw, and peat moss to your soils as well. We tend to use our cattle’s left over bedding, coffee grounds, ash and left over charcoal from the greenhouse’s wood fireplace, and egg shells to our plots. We also tend to leave much of the plant matter in our garden when the season ends that will break down over the winter and be tilled in the spring. Even things like cardboard can be layered in help build organic matter.
Microbiome
If you notice a lack of life in your soils you may want to consider inoculating it. These products bring desirable bacteria and fungi to your soils to help them break things down into usable nutrients, and sometimes have symbiotic relationships with the plants that grow with them. For example, mycorrhizal fungi can coat fine root hairs which help it absorb moisture and nutrients and protect it from disease.
Of course, you wouldn’t think of soil ecology without thinking about worms. Worms decompose organic matter, add nutrients via their waste, and create tunnels to battle compaction of soils and allow drainage. Adding these critters to your garden will only bring good things! Consider farming worms, making your own compost with food and lawn scraps, or having a safe space where they can grow so you can add them anywhere you please.
Measurements
The hardest part of all this is knowing how much of each product to add. While many products have guides on the back of their packaging, things like compost, straw, and lawn clippings will not. Also, those packages won’t know what state your soils are in and will likely be based on an already somewhat balanced soil. There are calculators online that can help specify the amount of nutrients you need based on the numbers your soil tests have provided.
Incorporation
Once you have the amendments you want and need, you must incorporate them into your existing soil. While Incorporating amendments in a small area is hard work when done by hand, is it definitely doable. In a large area, or in new developments with little topsoil, mechanical help will be much appreciated, if not needed.
There may be a hardpan from the construction of the house, and compaction of soil from the equipment for example. The hardpan can be broken with a chisel attachment, and the compaction can be removed with a heavy-duty tiller. A tiller will also make incorporating your amendments into the entire area relatively fast and easy. Most hardware stores rent out equipment for these jobs, and often neighbors and locals are willing to help with their equipment.
Up-Keep and Care
Your soils should be amended every year. Once it is healthy and workable, it should be as simple as adding a layer of compost annually. You can care for your soil as little or as much as you wish, just keep in mind that no soil can be worked forever and show no signs of deterioration. Your plants will ultimately suffer from bad soil conditions.
Here are a few tricks to help keep your soils healthy for years to come.
· Avoid pesticides and herbicides in and around your garden. While pesticides do kill off unwanted pests, they will also kill beneficial insects and microorganisms as well. If you do need to use a pesticide for an infestation, try natural products like neem oil, diatomaceous earth, or dish soap.
· Rotating your crops from place to place every year will make help keep certain areas from becoming nutrient deficient. For example, broccoli uses a lot of calcium, so by changing the placement of that crop every year, you ensure that the levels of calcium in your entire garden stay close to each other.
· Adding a layer of compost every year is a good habit to form early on. This brings new organic matter, nutrients, and microorganisms to your garden, which your existing soils will need.
· While testing is most important before your garden is started, be sure to test your soils every so often to be sure they are in tip top shape. Maybe your soils are already high in potassium to you don’t need to add potash every year. Also, the pH of your soil can change as things decompose or are added in.
· Keep records of your soil’s amendments, including the product names and amounts, noticeable changes in plant growth, any soil tests done, and changes that you see and feel in the soil from year to year. Not only will they help you learn more about what is working and what isn’t, it can make amending much easier by having a list of what you did the year before.
See? That wasn’t so bad. The science part can get a little intimidating but overall, taking care of your soil isn’t all that hard, it is so satisfying to see how the changes you make to your soil every year change the health of your plants! If you enjoy this aspect of gardening, I recommend reaching out to an extension office for more soil science related materials. We reach out to them every year or so with questions and concerns and they have always been happy to lend a hand and provide solutions.