By: Nikki Tilley, Author of The Bulb-o-licious Garden
Finding a good planting soil type is one of the most important factors to growing healthy plants, as soil differs from place to place. Knowing what soil is made of and how it can be amended can go a long way in the garden.
What is soil made of? Soil is a combination of both living and non-living materials. One part of soil is broken down rock. Another is organic matter made up of decaying plants and animals. Water and air are also a part of soil. These materials help support plant life by providing them with nutrients, water, and air.
Soil is filled with many living creatures, like earthworms, which are responsible for keeping the soil healthy by creating tunnels in the soil that help with aeration and drainage. They also eat decaying plant materials, which pass through and fertilize the soil.
Soil profile refers to the different layers, or horizons, of soil. The first is made up of decomposed matter, such as leaf litter. The topsoil horizon also contains organic materials and is dark brown to black. This layer is great for plants. Leaching matter makes up the third horizon of the soil profile, which consists mainly of sand, silt, and clay.
Within the subsoil horizon, there is a combination of clay, mineral deposits and bedrock. This layer is usually reddish-brown or tan. Weathered, broken up bedrock makes up the next layer and is typically referred to as regolith. Plant roots cannot penetrate this layer. The last horizon of soil profile includes unweathered rocks.
Soil drainage and nutrient levels are dependent on the particle size of a various soil type. The soil type definitions of the four basic types of soil include:
You can change the texture of various soils with additional sand and clay and by adding compost. Compost enhances the physical aspects of soil, which produces healthier soil. Compost is made up of organic materials that break down in the soil and encourages the presence of earthworms.
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Soil amendments for your organic vegetable garden! Amendments make your foundation, good soil, better. If you don’t have healthy, rich soil alive with good microbes, bacteria and organic materials you’re not going to have much of a harvest. I have a list of my favorites that I’ve used with success. You won’t need them all! I always recommend starting with the ones that you can get for free or nearly free first. Then consider testing your soil with a kit or using and seeing what additives would benefit you the most.
The topsoil here is full of organic material, with sandy soil beneath. Source: Holy Outlaw
Sandy soil does not have enough organic compounds. As it’s all larger particulate, the organic matter is necessary to help it retain water and nutrients.
You’ll need to amend the soil. The best way to do this is by incorporating compost or composted manure. It is dark, crumbly, and clings together, plus it retains water. Compost also contains plenty of vital nutrients for your plants in its organic material, and as that organic matter breaks down it slowly releases them to your plant’s roots.
Composts made from grass clippings, leaf mold, manure, food waste, and other similar products improve the soil. While adding sphagnum peat moss, coconut coir, or vermiculite can also amend sandy soils, these additions only improve the moisture retention capability of the soil. They do not address the lack of nutrients.
Apply 3 to 4 inches of well-finished compost or manure over the surface of your gardens and landscape beds and work it into the sandier soil.
Compost can also act as a mulch, especially if it’s a bulky compost with lots of larger bits. Spreading a thick layer of compost over your soil slows erosion and helps maintain soil moisture. It’ll gradually decompose and combine over time with your sandy material, dropping from the surface deeper into the bed. Applying more to top it off not only provides nutrients and soil improvement but will keep your plants happy and your beds weed-free.
Another convenient source of organic matter is growing cover crops. Planting a cover crop reduces weed growth in your garden beds. Later, you cut the plant and let it decompose into the soil. Common summer cover crops include cowpeas, pearl millet, and buckwheat. In winter, you can plant hairy vetch, mustard, and crimson clover. These crops are sown in bed and just as they near the flowering stage, they’re ready to till into the soil.
By tilling them into your sandy soil, you’re incorporating more organic matter. It will hang on to water for you, and as it decays it becomes its own fertilizer. Plus, they prevent erosion on the surface of your soil, and the plant roots prevent soil compaction.
The great thing about garden soil is that you can easily amend it to improve the quality of your soil. Before adding any of these amendments you will need to test your soil. The following amendments can be added to your garden soil:
Note: This section will make more sense if you read the fertilizers and soil sections first.
Soil amendments are not fertilizers
As discussed in the fertilizers section, plants need a number of different nutrients to survive. These nutrients can be purchased and applied to soil in concentrated forms called fertilizers.
Fertilizers are rated according to how much they contain of three critical plant nutrients:
Most fertilizers have labels that give you concentrations of N, P, and K as three numbers, like 4-6-4 or 6-2-0.
IMPORTANT: In the same place where they sell fertilizers, many garden stores also sell other products that are not really fertilizers but might seem like it at first glance.
These products, which this guide calls soil amendments, contain some of the same nutrients that fertilizers do, but in much, much smaller amounts. Soil amendments that have N-P-K labels may have numbers like 0-0.5-0, for example. Because they contain so few core plant nutrients, these products are not an effective way to provide most garden plants with nutrients.
What soil amendments are, and why you should use them
Soil amendments are made from a wide variety of materials, and they can be purchased in garden stores or made at home (if you have the materials, space, and time to make them). Manure from cows or horses is often used, as are various household and kitchen wastes (vegetable peels and cores, grass clippings, etc.). To make a soil amendment, these materials are processed somehow, usually by being made into compost.
Though this process can actually result in the loss of some nutrients, it makes the materials into a stable form of organic matter that is highly beneficial for your soil (see Intro to Soil for a discussion of organic matter and why it’s
important). You might wonder why gardeners don’t just add materials like manure, kitchen waste, and yard waste directly to their soil. There are several reasons for this. Fresh manure is neither very pleasant to handle nor very stable in the soil (it and the nutrients it contains can wash away, evaporate, etc.).
Manure can also carry disease- causing organisms that are killed by the process of composting. Other materials are harmless enough from health and environmental perspectives, but if you add them to your soil unprocessed, the result can actually be the removal of nutrients from your soil, at least in the short term. This occurs because the materials you add to the soil don’t just sit there – various creatures start to eat them immediately, and if the food you give them does not contain all of the nutrients they need to grow and reproduce, they will scavenge (collect) the nutrients out of the soil around them.
How much soil amendment to apply
Unlike fertilizers, which can be over applied, there is no upper limit to how much soil amendment you can safely put in the soil – the amount you put in depends on how much time, money, and energy you want to spend buying, making, and applying the stuff. It’s safe to say that you should add at least a small amount of some sort of soil amendment to part of your garden every year, and to the whole garden if you can. Gardeners who make their own compost (or who are willing to buy a lot of it) sometimes add as much as 5 cm (2 in) of compost across their whole gardens each year.
How to apply soil amendments
Soil amendments can be spread on a garden at any time of year, though it can make the most sense to do this at either the beginning of the year (when you are preparing a bed for planting) or at the end of the year (when you are preparing the garden for winter – see the garden through the season). Dump your soil amendment on the ground in a pile, and use a spade, spading fork, or garden rake to spread it around to the desired thickness. Then, use a spade or spading fork to work it into the ground. It doesn’t have to go in deeply -- a depth 20 cm (8 in) or less is enough just get it off the surface (it will break down faster and be less useful on the surface).
Mulch can count as a soil amendment
This section will make more sense if you read the mulch section first. Organic gardening is much easier if you use leaves, straw, newspaper, or some other kind of mulch to help control weeds. With the exception of plastic and landscape fabric, most materials used as mulch can be dug into the ground as described above once they are done performing their job.
Like compost and other soil amendments that you might make or purchase, these mulch materials contain organic material and can benefit your soil. They tend to contain very few nutrients, however (the fact that nothing wants to eat them this is partly why they make effective mulches).
Because mulches are nutrient-poor, if you incorporate large amounts of mulch and want to plant in the same place right away, you’ll want to add extra fertilizer to feed the organisms that are eating the mulch. If you don’t, they’ll take the fertilizer you intended for your plants and use it to complete their meals.
When choosing a soil amendment for your garden, it’s important to think about your soil’s pH level. Just like the soil, the amendments can be either acidifying or alkalizing. In case your garden soil has a high pH, it means it’s highly alkaline, so it means you shouldn’t add wood ashes as an amendment, since it also has high pH value. Instead, you should add a more acidic amendment, such as peat moss and compost.
Here are some of the best soil amendments you may use to improve your garden soil:
It’s best to add your pH amendments about one month before fertilizing and also well in advance of planting. After this one month, retest your soil. In case pH is still too high or low, give soil a second treatment. However, make sure to never apply more than recommended dosage. Remember, it may take years to fully amend your soil and change its pH levels.
Finally, it’s important to know there are some soils that come with special challenges when it comes to structure, texture or pH imbalances. These problems need to be addressed and corrected before you start planting.
Here are some of the most common problems and how to solve them: