Published in the June 21 – July 4, 2017 of Morgan Hill Life
By Kate Russell
Unless you’re using a syringe, you’ve never really fed or watered your plants. When you irrigate or fertilize your plants, what you are really doing is watering and feeding the soil. It is the soil that feeds and waters your garden and plants.
Creating healthy Morgan Hill soil is the best way to grow healthy plants that need less protection from pests and diseases, produce more flowers and food, and require less work. Let’s learn more about growing great soil.
What is great soil?
Soil is a highly complex natural body that some call the Earth’s living skin. Soil stores water and nutrients, filters our drinking water, helps break down toxic wastes, and is a critical player in carbon cycling, nitrogen cycling, and, let’s face it, life on Earth. Soil is made up of minerals, dead things, living things, gases, and liquids. Great soil has spaces that hold and allow water and gases to flow, carrying nutrients to your plants. Great soil is rich in organic matter that is made up of living things, and things that used to be alive. Great soil also contains the 17 primary nutrients required for plant development. But before you can grow great soil, you need to know what you already have.
What is in your soil?
The only way to really know what is in your soil is with a test from a reputable lab. The Olson test is better for the West Coast, while the Brays test is better on East Coast. In the Bay Area, we tend to have clay soil that is highly prone to compaction. Aeration is frequently needed. Clay soil tends to contain plenty of most of the necessary minerals, and too much salt and phosphorous. Iron and nitrogen deficiencies are common in the Bay Area. Your soil test results should include percentage ratings for each of the major plant nutrients. It may also tell you how much organic matter is in your soil.
Organic matter in soil
Organic matter is critical to soil health, and it can range from 1 to 8 percent. As living things die and begin to breakdown, they add nutrients and improve soil structure. They also alter the electrical charge of soil. Ensuring there is enough organic matter in the soil also improves porosity, aeration, and biological activity.
Soil is usually described as being sand, loam (silt) or clay. Sand is big. You can see individual particles. And water and nutrients can drain away quickly. Loam is made up of medium-sized particles that hold a good balance of gases, liquids, minerals and organic matter. Clay is made up of extremely tiny particles that can hold a lot of water and minerals. Organic particles surrounded by clay are protected from the microorganisms that break them down into nutrients that can be used by plants, creating an unattainable banquet. Each type of soil benefits from the following:
Sand — add organic matter to help it retain water and nutrients
Loam — add organic matter to help maintain the inorganic mineral and organic matter balance
Clay — add organic matter to improve soil structure and porosity, and to speed the breakdown of organic matter
Adding organic matter to soil is critical to plant health. A 1 percent increase in organic matter can make a profound difference in soil structure. This helps plant roots get to and absorb nutrients. You can add organic matter to your soil by:
• Mulching with untreated chipped wood
• Amending with composted kitchen and yard scraps
• Incorporating aged manure from local horse and cattle farms
• Raising chickens and composting their soiled bedding
• Protecting bare soil with ground cover crops
• Applying organic top dressings
Once you’ve increased the amount of organic matter, you will want to add nitrogen. Nitrogen levels are the single most limiting factor in most gardens, and organic matter can help plants access the nitrogen already present. Most soils contain less than 1 percent nitrogen, while 2 to 5 percent is ideal. Which form will you use? Inorganic nitrogen can be found as nitrites or ammonium. When roots take up nitrates, they increase the pH of the immediate area, making it more alkaline. The opposite is true when plants take up ammonium, making the soil more acidic. Organic sources of nitrogen include blood meal and cottonseed meal, both of which will acidify soil.
You can’t know which form of nitrogen is right for your soil until you know its pH. Soil with a low pH makes it harder for plants to access some macronutrients. Soil with a high pH does the same thing. Most plants prefer a pH of 6.0 to 6.5 to thrive. Growing great soil means identifying and managing your soil’s pH.
Creating healthy soil
Soil creation is called pedogenesis. You can create great soil in your garden and landscape when you:
1. Learn what you already have, with a reliable soil test.
2. Regularly incorporate organic matter with compost, mulch, and even coffee grounds.
3. Analyze your soil structure and aerate, as needed.
4. Only add needed amendments, and in the proper form for your soil.
5. Determine your soil’s pH.
Other ways to improve your soil’s health is by growing cover crops, using crop rotation, installing foot paths to reduce compaction, and avoiding irrigation run-off and urban drool.
For more information, visit www.mgsantaclara.ucanr.edu/events/ or call (408) 282-3105 between 9:30 a.m. and 12:30 p.m., Monday through Friday.
Kate Russell is a UCCE Master Gardener.
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