From the Ground Up: The Dirt on Soil
Soil is truly the foundation of any garden, but what is it?
Soil is alive! It is made up of minerals, nutrients, organic matter, and particles – primarily silt, sand, and clay — and contains water and microorganisms. Soil also has a certain acidity or alkalinity, which is measured by pH.
Texture and pH
The proportions of silt, sand, and clay particles determine the soil’s texture and can affect drainage. Clay particles are very fine and tend to stack, which can make it difficult for water to pass through or be stored. A high amount of clay can make soil very dense and difficult to work with. Meanwhile, sand does a poor job of holding on to nutrients. Ideally, there would be a balanced mix, creating what is known as a loam.
The pH scale runs from 0 to 14; 7.0 is considered neutral, while less than 7 is acidic, and above is alkaline (or basic). The importance of pH to your garden is that it can affect the availability of nutrients and concentrations of minerals in your soil.
Nitrogen (N), Phosphorus (P), Potassium (K) are the three primary nutrients in soil that affect our plants. How each of these is used by plants can be remembered by “up, down, and all around.”
- Nitrogen is used for leaf growth and good green color.
- Phosphorous helps form new roots, as well as make seeds, fruit and flowers and fight disease.
- Potassium helps support strong stems and steady growth, while also helping plants tolerate stress, like extreme temperatures, drought, and pests.
If your soil is low in one of these nutrients, you might notice these symptoms:
- Low nitrogen (N): Pale green or yellowing older leaves, undersized leaves, or short or weak stems.
- Low phosphorus (P): Red or purple tinges to leaves that are supposed to be green, or leaves with twisted or irregular shapes.
- Low potassium (K): Lower leaves that are dead at the edges or in spots, or are wilting.
A soil test can provide information on texture, pH, and nutrients. For a nominal fee, your local Cooperative Extension can perform one, resulting in information about your soil as it exists and any deficiencies, as well as steps that you can take to amend it. Learn more about Cooperative Extension services nationwide here. If you’re in New York, services are provided by Cornell University. To take a soil sample, dig down into the soil about 4-6 inches (this is where most roots would be) and collect about two cups worth of soil. If you’re hoping to plant in a larger area, it may be best to take a few samples for testing. It may take a few weeks to get your results back, so plan ahead if you can.
While a soil test can tell you pH levels, you can also try a pH kit (available in many garden centers). Most plants that we grow in gardens — vegetables, grasses, and most ornamental flowers — like a fairly neutral pH, just slightly on the acidic side (between 6.0 and 7.0). Plants like azaleas, rhododendrons, and blueberries like the soil a little more acidic.
Making Soil Improvements
Adding organic matter can help to improve texture by loosening compacted soils and also adding beneficial microorganisms that help with nutrient uptake. Organic matter can come in the form of shredded leaves, composted aged manure or yard and garden trimmings, mushroom compost, and straw or finely shredded bark mulch.
If your pH level needs to be adjusted, lime will increase the pH, while sulfate and sulfur will lower it. The amount of amendment you need to add, and how often, can vary based on your soil type.
Soil test results can help you confirm the nutrient levels, so that you know what is missing and add in only what your plants need. The numbers on bags of fertilizer represent the ratio of nitrogen, phosphorus, and potassium that they contain. For example, a label that says 12-6-10 means that it has 12% nitrogen, 6% phosphorus, and 10% potassium. Always make sure to apply according to the package directions. When it comes to fertilizers, you CAN have too much of a good thing, and it can harm your plants.
To support plants that are strong and healthy, the soil must be healthy and fertile. A healthy soil system provides plants with access to the air, water, and nutrients that they need. Doing a little investigating into your soil can save you from troubleshooting problems during the season and battling excessive pest and disease issues. Improving your soil takes time and is an ongoing process. Just remember, like all living things, soil must be fed regularly.