Soil 101: Basic Requirements For Healthy Soil.

I have said before that good soil is the foundation of every garden, but that’s not true. Soil is more the foundation, the walls, the windows, the ceiling and the doors. The plant material is just the furniture you add to the space to fill it. In other words: we cannot overstate the importance of good soil! But what is it and how can we make sure we get some of that good stuff?

Soil is a complex ecology that needs to have a healthy balance for plants to thrive. It is a mixture of ingredients that everyone with a “green thumb” understands, whether they are working in the yard, in the greenhouse or tending indoor plants. In this article we will examine those different ingredients and how they come together.


Roots require air as well as water, and aeration is, quite literally, the practice of getting that air into the soil. Without the air the ground might become waterlogged and the plants could drown. The first requirement is a good soil mix, or whatever amendments are needed for the existing soil. A combination of regular dirt with sand (inorganic matter) and compost (decomposed organic matter) works wonders for any planting medium. Another great aerator is the earthworm. As they burrow through the soil they break it up and increase the natural tilth. Having a healthy ecosystem always means having worms. If you dig into your own garden and don’t find any it is a big red flag. But don’t worry, you can always buy some and add them to the beds. And, incidentally, if you dig and find red soil – that’s a big red flag, too!

Organic Matter

This is compost. Decomposed plants, food scraps, manure and leaves. Mixing it into soil will add nutrients, increase hydration, aid with the nutrient intake of root systems, promote beneficial microbial life to keep soil healthy, aerate, adds CO2 for better plant growth, and buffers the soil pH keeping it neutral. Basically, if compost was a girl, everyone would want to date her!

Moisture-Holding Ability

These next two paragraphs may seem like a contradiction in terms, but no. Soil needs to be able to hold onto moisture so that the root systems of plants can absorb it. If a planting medium is nothing but sand or rocks the water’s going to be gone before most plants can get a drink. This is why it’s important to have composted material in the soil to help with this. Also, a little clay is beneficial, and is usually present in most soil. However …

Good Drainage

Too much clay will hold the water in the soil indefinitely. This is bad for the root systems in a number of ways. As we have mentioned, if the soil is waterlogged a plant can drown, but also it would cause salt retention. All soils have natural salts, which are normally fine, but if they are allowed to build up they can become toxic to many plants. The only way to flush these salts out is, of course, with water. This problem can be remedied by the addition of inorganic material such as sand or decomposed granite. And we’ve all seen the perlite mixed in with soil in potted plants, and while that is an artificial material, it does the same job.

Proper pH Level

A neutral pH level is between 6.5 and 7.3. Anything outside this on the 1-14 scale and plant health begins to suffer. In acidic OR alkaline soil roots struggle to properly process and absorb nutrients, especially iron, and may appear sick and diseased with iron deficiency even if the soil is full of iron! Many folks see this yellowing and throw more iron at the plants and wonder why they don’t get better! The solution depends on the problem For overly alkaline soil add compost, gypsum or sulfur; for acidic soil add wood ash or limestone. Determining the pH of your soil is necessary to determine what problems you might have. To do this you can send a sample to a professional lab (which is expensive), buy a cheap test kit and hope it’s accurate, or do the old standby and get some litmus papers. Dip them in a solution of your soil and see what color it turns. That will correspond to any pH color chart.

Healthy Microbial Life

Microbes such as bacteria and fungi break down organic matter into more basic compounds. Unfortunately there are the good types which provide nutrients, and bad types which provide disease. I’m not sure what happened to the ugly. So, when microbes are in short supply the more likelihood there will be of diseases and nutrient deficiencies. The solution is the addition of decomposed organic matter. That will provide a healthy environment that will promote microbial life. Aah, compost … is there anything you can’t do?

Low Salt Content

We’re not just talking about good old sodium chloride you get on your fries here. Salts are formed when acidic compounds react with alkaline compounds. The biggest culprits here are fertilizers. Even organic fertilizers can potentially have high salt content. The rule of thumb is: always follow the instructions from the fertilizer manufacturer. Never over-fertilize. In this case more is not merrier. Or how about this for a concept: don’t fertilize at all. If you already have a good amount of compost mixed in you shouldn’t need to. You are providing all the nutrients a plant should need. If you do have a salt buildup from over-feeding in the past, all is not lost. Salts do dissolve and move with water, so if your soil test reveals a bounty of saltiness a deep watering will help move it on down below the root systems.


So, in conclusion: aah, compost …