Generally speaking, there are two different types of soil amendments. You’ll find man-made (inorganic) amendments and natural or organic amendments.
There are pros and cons of both types, and both have a place in modern gardening.
In this article, we will focus on organic soil amendments.
These are treatments for your garden soil that you can make using biosolids, leaves and straw and other natural materials like:
When comparing organic and inorganic soil amendments, it may seem that the inorganic variety is preferable because it delivers a bigger boost of nutrients.
However, this does not always produce a desirable effect. In the long term, organic soil amendments deliver more nutrients in a steadier and more usable fashion.
Organic soil amendments work to improve overall soil condition as well as deliver nutrients directly to your plants. In the long term, well-conditioned soil creates its own nutrients and replenishes the needs of your plants on a regular and ongoing basis.
When you provide the soil with a stable and constant supply of nutrients, not only will your plants grow in a more healthy manner, beneficial flora and fauna such as earthworms, friendly bacteria, and helpful fungi will benefit.
Adding quickly decomposing organic soil amendments such as grass clippings and manure can provide a quick boost of nutrients. Combining these with more slowly decomposing organic material such as wood chips and peat can help provide aeration in the soil.
If you make potting soil, add vermiculite and perlite to improve aeration. To loosen soil naturally, you can also add pea gravel. This really benefits soil with high clay content. Adding coarse material helps open up the soil to allow more air to penetrate it.
Surprisingly, another good product for amending clay soils is finely chopped-up rubber tires. Although the rubber tire material is not organic, this type of technique does have a place in organic gardening. It’s smart recycling of a non-biodegradable resource, and it works well to improve the quality of garden soil.
It is very rare to find perfect soil. Most gardeners struggle with too much sand, too much rock, too much clay, acidity, and more.
Luckily, transforming your soil from poor to perfect is not impossible. It does take a series of specific steps depending upon the type of problems with your soil. In this section, we’ll explore targeted treatments for a variety of soil conditions.
Soil is made up of four elements:
These form the basic building blocks, but they are not the components that cause your soil to be a life-giving substance. Truly healthy soil requires a thriving population of friendly fauna such as:
Balancing the first four elements will help you attract and maintain these natural garden helpers.
About half of your garden soil is made up of weathered rock that has been broken down over long periods of time by natural elements such as:
The size of inorganic mineral particles found in your soil determines the type of soil you have. Soil types are:
While the inorganic matter in your soil determines soil type, the organic matter determines how nourishing your soil will be. Organic matter is made up of partially decomposed living things such as:
These substances only make up a very small percentage of your soil (5 % to 10 %) but are absolutely essential. Organic matter helps soil particles bind together to become porous granules or crumbs that let water and air move freely through the soil.
Additionally, organic matter helps soil retain moisture. In fact, humus is capable of retaining as much as 90% of its weight in water. This makes it able to absorb large amounts of nutrients and store them efficiently.
The organic matter in your soil provides food for friendly flora and fauna and for the plants you grow. For this reason, it’s easy to see how important it is to add organic soil amendments such as:
Using these nourishing amendments on a regular basis is easy because they only need to be worked into the top six inches of your soil.
For this reason, you can simply add top layers of compost and other organic matter in the form of mulch on a seasonal basis. Till these in at the end and at the beginning of the growing season to keep your soil well amended.
Healthy organic soil is living soil. It is filled with all manner of minute thriving beings. Among them are:
These tiny creatures help to convert the soil minerals along with the organic matter that you provide into disease suppressing compounds, nutrients, vitamins, and hormones that are absolutely necessary to successful plant growth.
Additionally, the excretions of these living things help bind soil particles to create the small aggregates that loosen your soil and help it to attain a crumbly texture. It’s easy to see that as a successful gardener, you will be far better off focusing on creating ideal soil conditions to support these organisms than on simply providing plant nutrients.
When you provide friendly flora and fauna with abundant sources of:
…you can count on having soil that naturally provides your plants with all of the nourishment they need.
You may not realize it, but about a quarter of your soil is simply air. Like all living things, the friendly flora and fauna that live in your soil need ample air to survive.
When your soil is well-aerated, you can be sure that it contains the amount of atmospheric nitrogen your plants need. Additionally, soil that is well-aerated has a good percentage of pore space between soil crumbles and particles.
The right amount of pore space is very important. Soil that has very fine particles (e.g. silt or clay) does not contain enough air to support life.
Soil that has excessively large pore space (e.g. sand) may have an excess of air which will cause your organic matter to decompose very rapidly.
A proper balance of air is essential to healthy soil life, so you must be sure to add organic matter to your soil on a regular ongoing basis.
Furthermore, you should avoid walking on your tilled garden soil because doing so will compact the soil. Avoid using heavy equipment and simply let your soil rest after heavy rains.
Just as a quarter of your soil is made up of air, another quarter is made up of water which is also held in the soil pore spaces. Having the correct size of pore space is just as important for the distribution of water as it is for the distribution of air.
When the spaces are too small, water cannot penetrate the soil. When they are too big, water rushes through too quickly and washes away nutrients.
Additionally, soil that has excessively large pore spaces cannot retain water and dries out rapidly.
A healthy balance of small and large pore space is ideal. To create this condition, you must add organic matter on a regular basis to encourage the formation of crumbs and particles in the soil.
A proper balance of organic matter absorbs water and holds it so that it will be easily accessible to your plants.
Adding organic matter in a regular and consistent manner is key to creating the right combination of qualities to facilitate the most effective and efficient processing of air and water.
It’s easy to determine the texture of your soil. Just take a pinch and put it in the palm of your hand. Add a little water and then rub the mixture between your thumb and forefinger. Gritty feeling soil is sandy soil. Smooth soil is silty soil.
Clay soil is a little bit more complex. It will feel harsh when it is dry and rubbery when it is wet. It may also feel slippery or sticky when it is wet.
The various textures of soil have been created by geological events. Silty soil is soil leftover from an ancient floodplain. It is very different from the stony soil you will find in mountainous regions.
If your soil consists of very high clay content, this is an indication that it was once buried beneath a glacier. If your soil has high sand content it may have once been underwater (i.e. near or at the bottom of the ocean).
The most important thing to know regarding soil type and texture is that good management makes it possible to correct all manner of soil issues.
The fingertip test is a good way to get a general idea of the type of soil you have, but you can get more precise results with a simple jar of water. Use a mason jar, mayonnaise jar, or similar quart-sized jar with a lid to conduct this test.
Knowing the makeup of your soil is so important to help with watering, fertilizers, and more. Now is a good time to find out!
In order to determine what type of soil amendments you need, you must not only become very familiar with the type of soil you have. You must also understand the needs of the flowers and crops you wish to grow.
All soil amendments are not created equal, and an amendment that would work well in sandy soil would be very unlikely to work well in clay soil, for example.
When you have received disappointing news about the condition of your soil, you may wish to turn to seaweed as an excellent overall soil conditioner. It contains a minimum of 60 micronutrients that include:
Although seaweed is not complete as a fertilizer, it is a very desirable soil amendment that can provide very valuable support for any soil building program.
Seaweed boosts your plants’ immune system and helps them to fight off insect pests, viruses and bacteria.
Additionally, seaweed contains high concentrations of naturally occurring growth hormones. This support increases root growth and helps plants overcome transplant shock.
Furthermore, when you use seaweed as a soil amendment you can expect fruit to set more rapidly, and expect your plants to resist frost more effectively. When you have harvested your fruits, you will find that they have a longer shelf life.
It’s easy to amend your soil by distributing powdered seaweed (aka kelp meal) over the surface of the soil and watering it in. As a powder, it releases nutrients in a gradual manner.
For quick pick me up, you can give your plants a treat of liquid seaweed. Like other liquids from plant fertilizers, this product makes nutrients available immediately.
Very sandy soil is made up of fairly large and irregularly shaped granules of rock.
Remember that sandy soil has very large pore spaces between its particles, so water will drain away from they very quickly carry nutrients with it.
Your goal with sandy soil will be to make the pore spaces smaller so that they can retain water and nutrients. This will help support a thriving population of friendly soil flora and fauna. Here’s how:
Clay soil is very dense with very small, or nonexistent, pore space. Wet clay soil is sticky and very difficult, if not impossible, to work with.
Drainage is slow, which causes waterlogging of your plants. Once clay soil becomes dry, it also becomes hard and cracked.
A lack of pore space indicates a lack of organic matter and the subsequent dearth of microbial activity. Here’s how to fix this problem:
Although silty soil is very fertile, it is also very dense and tends to have quite a small pore space. This type of soil is made up of very small irregularly shaped weathered rock particles.
You can amend it to take advantage of its superior fertility by following these steps:
The pH level is the relative alkalinity or acidity of your soil. When you take a pH test of your soil, you measure the ratio of positive ions (hydrogen) compared to negative ions (hydroxyl).
When these two elements are equal, your soil will have a neutral pH reading (i.e. pH 7). If your soil contains more positive hydrogen ions, it will be acidic with a pH reading between 1 – 6.5.
If your soil contains more negative hydroxyl ions, it is considered alkaline with a pH reading ranging from 6.8 – 14.
It is best to set your goal for a fairly neutral pH level hovering around a solid 7. It is at this pH level that most plant nutrients can be absorbed.
With a very high or very low pH level, the nutrients in your soil will become chemically bound to the soil particles. When this happens, your plants will not be able to access the nutrients and will suffer and possibly die.
It’s important to understand that balancing the pH level of the soil is a gradual process. You need to amend your soil regularly and in a consistent manner for several growing seasons to exact any lasting change.
Once you have adjusted the pH levels, you will need to continue adding liberal amounts of organic matter to the soil to help keep those levels in balance.
If you live in the eastern US, don’t be too dismayed if you find your soil with fairly high acid levels. This is common throughout the Eastern states.
If your pH test reveals your soil has a pH level of less than 6.5, you will need to make some adjustments unless you are planning to grow acid-loving plants such as Azaleas and blueberries.
In order to raise your soil’s pH level and reduce its acidity, it’s a good idea to add some powdered limestone.
When you apply dolomitic limestone in the autumn of the year, you’re taking a positive step to reduce your soil’s acidity and also to add a healthy dose of manganese.
As your garden bed lies dormant through the winter months, the pH level will adjust gradually. Remember you will need to continue treating your soil on a regular ongoing basis for several growing seasons.
For minute adjustments in various types of soil using limestone, follow these guidelines:
One of the uses for wood ash is for a quick acidity adjustment which will also deliver a healthy dose of essential trace elements and potassium to your soil. You must be careful not to add too much, though.
Adding excessive amounts of wood ash can alter your soil’s pH levels vary drastically and cause imbalances. The best thing to do is wait until wintertime and then scatter a couple of pounds per 100 square feet to the surface of your garden area.
Do this before rain or snow, or simply water the amendment into the soil well. You can repeat this treatment every couple of years.
If your testing reveals a pH level of greater than 6.8 (as is common in the Western United States) you need to take steps to acidify the soil.
The best way to do this is to add ground sulfur, but some other organic materials are also naturally acidic and can be used. Examples include:
Working these natural organic choices into your soil in wintertime and/or using them as mulch in the spring and summer can help to alkalize your soil.
You can also use sulfur in measured amounts to lower the pH reading of your soil one point at a time. Here’s how:
In addition to telling you the pH levels of your soil, professional soil testing gives you a great deal of information regarding the structure and nutritional value of your soil. For example, a professional soil test can tell you about your pH levels and also give you an idea of how much:
… Your soil contains. This valuable information will help you in choosing the right amendments for your soil.
To learn about having your soil professionally tested, talk with your local cooperative extension service. They may offer testing free or for a nominal charge. If your co-op does not offer soil testing, get in touch with an independent soil lab.
A good soil testing lab will give you well-informed recommendations regarding the specific organic amendments you should use to make adjustments to your pH levels and make your soil as nutritious as possible.
Be advised that labs closest to you and labs in your own region will probably be of the most value to you.
For the very best results, send soil samples from several areas of your yard and garden. For example, you could take a sample from your vegetable garden, your flower garden, and also from your lawn.
It’s best to conduct your soil testing in the spring and also in the autumn. At these times, the soil is at its most stable. These are also the best times to make amendments to your soil.
Green manures and cover crops provide a way of protecting, preparing, and enriching soil structure before it is used. For example, you might plant a cover crop over an unused area of your garden bed during the wintertime.
A cold-hardy crop such as winter ryegrass or vetch will protect the soil through the winter. When springtime comes, you can till this crop under to add more nutrients to the soil.
… are considered green manures. Like manure, they provide a great deal of nitrogen and organic matter to your soil. As a bonus, they grow very densely and choke out weed growth.
With green manures, you can harvest their produce and then till the plants under to enrich your soil.
With either cover crops or green manures, you must be sure to till them under a minimum of three weeks prior to replanting the area. This will give the organic matter a chance to begin decomposing by the time that you are ready to plant.
Garden researchers have recently been able to isolate certain organic substances that can solve very specific problems with the soil. Liquid, organic soil conditioners can now be formulated to produce exact results such as:
A liquid soil conditioner usually consists of a combination of catalytic enzymes and humic acid, which are usually produced by the natural microorganisms in working compost. With these commercial soil conditioners, the ingredients are produced in a lab environment.
Liquid soil conditioners can be very valuable when working with stubborn soils (i.e. clay or sand).
A good liquid soil conditioner helps clay soil become more workable and makes more nutrients available to your plants. That same conditioner can help sandy soils to retain more water and more nutrients.
Clearly, soil amendment can be a very complex topic. It may take you a while to familiarize yourself with the qualities of your soil and to determine exactly which actions will produce the best results. Use the information presented here as a springboard to get started on making the most of the garden soil you have.
