Soil Part II: Keeping Your Soil Healthy

In our last post we learned that having healthy topsoil in your garden is extremely important when it comes to your garden’s success. Unfortunately, the reality is that most people do not have great quality soil in their backyards. If this is the case for you, don’t stress about it. Thankfully, there is a lot that you can do to improve and maintain the quality of your soil. If your soil thrives, your garden will too!  ​

Image by Catherine Ulitsky

Let’s start by recapping the characteristics we want in our soil. Healthy garden soil:  

• Contains lots of organisms like earthworms and nematodes, which make nutrients accessible and aerate the soil.  
• Has plenty of humus, or decomposed organic matter.  
• Contains nutrients like potassium, nitrogen, and phosphorus.  
• Has good drainage and water retention. 

• Is nicely aerated so plant roots can grow easily. 
• Has a pH between 6 and 7.5. 

Now, if your soil is less than ideal, the way to improve it is to add stuff to it each year. This is called amending the soil. The amendments should be added when you are preparing your soil for planting or when transplanting your seedlings, both of which we will cover later.  

The bad news about soil amendments is that they can quickly add up to become one of your greatest gardening expenses. People can easily spend hundreds of dollars layering rich soil, store-bought compost, manure, fertilizer, and mulch over large areas of their garden. While plants will certainly appreciate this type of treatment, if you are gardening on a budget, please know that you don’t need to go overboard trying to achieve perfect soil. Whatever amendments you can afford to add to your soil will help. The basic goal is to introduce some nutrients to your soil to help your plants grow healthy and produce a decent amount of food. The following tips are most useful for folks who will be using in-ground beds, but they could also be helpful for those using raised beds filled with unfamiliar soil. (Containers should be filled with high-quality potting mix, not dirt from the ground.) 

A good place to start when trying to figure out what amendments your soil needs is to do an inexpensive soil pH test, which you can buy from gardening centers. If your soil has a pH that is lower than 6 (which means it is very acidic) or higher than 7.5 (which means it is very alkaline), you will need to add ingredients to your soil that will help change its pH. For example, you can make extremely acidic soils less acidic by adding lime (pulverized limestone) and extremely alkaline soils less alkaline by adding peat. These are also sold at gardening stores, and the packages should contain instructions on how much product to spread over a certain area of land.  

If your soil pH is already between 6 and 7.5, you might still have a problem with your soil containing a lot of sand or clay. The only way to change this is to add organic matter to your soil. Over time, decomposers like bugs and earthworms will incorporate the organic matter deeper into the soil and transform it into humus, which will add nutrients to the soil, make clay soil less dense, and help sandy soil retain water better.   

Soil that is dark and crumbly likely contains a good amount of humus. Image by USDA.

As we discussed before, compost is one of the best organic (natural) amendments you can add to your soil. You can either use compost that you have made yourself or purchase commercial compost, which is often made from decomposed, odor-free cow manure. When preparing your soil for planting, you can incorporate a few inches of compost into the top layers of your garden soil. This calculator will help you find out how many bags of compost you will need. If you can’t afford to buy a lot of compost, you can apply the compost in a foot-wide radius around each of your plants instead of all over your garden bed.  ​

Other organic matter amendment options include manure from grass-eating animals such as chickens and rabbits, peat moss, used coffee grounds, grass clippings, wheat straw, worm castings, and sawdust and ashes from untreated wood. The Craigslist farm and garden section is a great place to search for people in your area who may be selling some of these materials for cheap. 

While adding organic matter to your garden will help to condition (improve) the structure of the soil, it will not add enough nutrients to give you the type of larger yields that can be achieved by using fertilizer. For this reason, I recommend adding an slow-release fruit and vegetable fertilizer to your soil as well. Like compost, you can spread the fertilizer all over your garden bed or apply it in a radius around each plant according to the instructions on the package.  
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Plant fertilizers can be chemical or organic. Chemical fertilizers are man-made and contain high levels of essential nutrients. Organic fertilizers are composed of naturally occurring materials like bone meal and potash which provide lower levels of nutrients. Whenever you buy a fertilizer, look for the NPK value, which will tell you what percentage of nitrogen (N), phosphorous (P) and potassium (K) the fertilizer contains. These are the three essential nutrients that plants need. For example, an NPK of 10-20-10 means that the fertilizer contains 10% nitrogen, 20% phosphorous, and 10% potassium by volume. Generally, you want the middle number to be higher than the other two numbers, though a fertilizer with all equal numbers works too.  

An organic slow-release vegetable fertilizer with an NPK of 2-5-3. The NPK of organic fertilizers is often lower than that of chemical fertilizers.

In addition to adding organic matter and fertilizer, you can keep your soil healthy by avoiding soil compaction. This is when soil becomes hard and dense by people walking or heavy things driving over it. Once you plant your garden, try to avoid walking over your garden bed as much as possible, especially close to your plants.  
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Another way to keep your soil aerated is to make sure that you have organisms like earthworms living in it. You can check this by digging into your garden. If you come across a few worms, you’re in good shape. If there are few organisms in the soil, adding organic matter to the soil should attract them. You can also purchase earthworms to release into your garden (just make sure the kind you buy are native to your area!) ​

Earthworms are an indicator of quality soil. Image by Lynda Richardson.

Adding organic soil amendments should improve your soil’s drainage and water retention, but I also strongly recommend covering the surface of your soil with mulch or a thick layer of straw after you’re done planting. These materials will help keep moisture in the soil, prevent a hard crust from forming on top of your soil, and suppress weeds! You can get cheap mulch in large amounts from your town’s yard waste facility or local tree service, which will often deliver the mulch directly to your home.  

Lastly, when planning your garden layout next year, make sure to move your plants around. Plant your tomatoes where your corn was last year, and vice versa. This is called crop rotation and ensures that a single vegetable does not deplete all the nitrogen or all the phosphorous from one area of your garden. You should also consider planting a cover crop like barley or red clover in your garden at the end of the growing season. These crops help keep the soil aerated during the cold season and replenish certain nutrients that your vegetables use up each year. You can even eat some of them!  

Building great soil takes time. If you follow these tips, your soil will only become better from year to year.  
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As always, if you have any questions or tips to share, please comment below! ​