This is the second in a series of posts about fostering and maintaining healthy soil in your farm or garden.
In our first soils blog post, we learned about soil physical properties, including texture, structure, and how different soils hold or release water. Now that we have the physical properties covered, we’ll explore the chemical properties of soil, as well as our top 10 favorite organic soil amendments to give your soil the nutrients it needs to cultivate happy and thriving plants.
Mineral Nutrients
In order for plants to thrive, they need access to certain nutrients in the soil. The living organisms in healthy soil access nutrients in rocks through chemical processes, make them available to plant roots, and then recycle these nutrients from decomposing organisms back into available forms every season. (We’ll talk more about biological properties in the next article.)
This process is called mineralization, and in soils that don’t contain healthy microbial life and organic matter (humus), they can be leached away into our watersheds. This leaching is what happens in lifeless soils on conventional farms where nutrients are applied as fertilizers with little regard for the health of the soil. Some of the nutrients applied as fertilizers make it into the plants but most of it gets leached out of the soil and becomes pollution in our groundwater, rivers, and oceans, causing all kinds of damage.
The three key nutrients are nitrogen (N), phosphorous (P), and potassium (K), but there are also many other nutrients and micronutrients that plants depend upon. Each plant has different nutrient needs, so be sure to look up any special nutrient needs for plants you intend to grow and design your soil plan to meet those needs if you find out your soil is deficient.
You can sometimes see nutrient deficiencies through how your plants grow–or not–in your soil. However, the best way to assess your nutrient profile is through a lab soil test.
pH
Another factor to assess with a lab test is the pH, or acidity, of your soil. Plants require a certain range of acidity in order to thrive. Most vegetable crops grow best with a 6.2 to 6.8 pH level (Gershuny 183). This varies by crop, and some crops like blueberries actually prefer more acidic soils. For general gardening and farming, an ideal range is 6.2 to 6.8, and a lab soil test will tell you if your soil is in range.
These factors are important to assess early on so that if your soil is out of the ideal range, you can begin improving your soil with compost, cover crops, careful and intentional tillage (if you plan on tilling), and carefully measured supplemental nutrients.
Soil Testing
Lab soil tests are the best way to assess nutrient deficiencies and pH issues with your soil. To learn how to take a sample and interpret the results, please see the first post in this series.
Our Recommended Top 10 Organic Amendments
So you got your soil test results back from the lab, and you need to give your soil some love. It can be easy to get overwhelmed by the many recommendations online and in the gardening store, so we’ve compiled our tried and true list of top 10 organic amendments to improve your soil.
1. Dolomitic lime
- What it’s used for: It raises the pH of your soil and contains magnesium and calcium.
- When to apply: Add dolomitic lime to the soil before planting.
- Where to get it: Most garden stores carry it, such as San Lorenzo Garden Center.
- Learn more about dolomitic lime.
2. Gypsum
- What it’s for: Gypsum raises the pH of your soil. Over time it helps break up soil compaction to give plants more room to grow, particularly in clay soils. It also contains calcium and sulfur
- When to apply: Add gypsum to the soil before planting.
- Where to get it: Most garden stores carry it, such as San Lorenzo Garden Center.
- Learn more about gypsum.
3. Soft rock phosphate
- What it’s for: It’s a source of phosphorus and calcium.
- When to apply: Add soft rock phosphate to the soil before planting.
- Where to get it: Most garden stores carry it, such as San Lorenzo Garden Center.
- Learn more about soft rock phosphate.
4. Aged horse manure
- What it’s for: It’s great for building soil structure. On average, it contains 0.6% nitrogen (N), 0.2% phosphorus (P), and 0.4% potassium (K).
- When to apply: Be sure you are using aged/composted horse manure–not raw. Apply before planting for crops that will not come in contact with the soil. You can also use horse manure to make compost.
- Where to get it: It is easy to source from local stables, such as the Felton Covered Bridge Horse Stables, 220 N. Covered Bridge Rd. Felton, CA 95018. They have a front end loader and will load the manure into your truck for a small fee. Be sure to bring a tarp and tie downs so your precious cargo doesn’t fly all over the road. Note: When selecting a stables to get manure from, beware of weed seeds in the manure if it has not been composted correctly. Also ask about their de-worming practices. Some people over do it and de-worm their horses on a regular schedule “just to be safe” while most only use de-worming antibiotics when there is a problem. The latter is better.
- Learn more about aged horse manure.
5. Compost
- What it’s for: It adds organic matter, improves soil structure, and increases the ability for soil to hold moisture. Compost also releases nutrients (NPK) slowly over time, including micronutrients. Note that different composts will have different nutrient profiles depending upon what the compost was made with.
- When to apply: You can apply compost before, during, or after planting.
- Where to get it: Local sources for commercial bulk compost include Central Coast Compost, Herbert Family Farm, mushroom compost from Central Home Supply, and you can also buy bags of compost from the nursery. We recommend making your own compost if you have the space for it! It’s cheaper than buying compost, it allows you to reduce food waste by turning it into a valuable nutrient for your plants, and it’s fun!
- Learn more about making your own compost.
6. Chicken manure
- What it’s for: On average, it contains 1.8% nitrogen (N), 2.7% phosphorus (P), and 1.5% potassium (K)
- When to apply: Fresh chicken manure can harm your plants, so typically aged chicken manure is used. Apply aged chicken manure before planting for crops that will not come in contact with the soil. You can also use chicken manure to make compost.
- Where to get it: Local egg ranches, such as Glaum egg ranch, friends who keep chickens, or your own chicken coop!
- Learn more about chicken manure.
7. Pelletized chicken manure
- What it’s for: It provides NPK similar to fresh or aged chicken manure, although most brands have varying nutrient levels depending upon your needs. In a vegetable garden or farm, an NPR ratio of 4-6-4 is recommended.
- When to apply: You can apply pelletized chicken manure before, during, or after planting.
- Where to get it: Many local nurseries carry pelletized chicken manure, such as Sustane © brand which is OMRI-certified (learn more about OMRI below).
- Learn more about pelletized chicken manure.
8. Fish emulsion
- What it’s for: On average, it contains 5% nitrogen (N), 1% phosphorus (P), and 1% potassium (K), as well as micronutrients
- When to apply: Fish emulsion is a liquid that you dilute with water before applying. You can apply it to the soil around the plant root zone. You can also apply it as a foliar spray to the leaves of plants. Fish emulsion can be applied to plants in the greenhouse, in pots, or in the ground.
- Where to get it: Most nurseries carry fish emulsion, such as Alaska brand, which is OMRI-certified (learn more about OMRI below). If you’re adventurous and don’t mind the smell of rotting fish, you can also make your own!
- Learn more about fish emulsion.
9. Liquid kelp
- What it’s for: It contains micronutrients that benefit plants in numerous ways.
- When to apply: Liquid kelp usually comes in a concentrated form that you dilute with water before applying. You can apply it to the soil around the plant root zone. You can also apply it as a foliar spray to the leaves of plants. If you are ferti-gating (fertilizing + irrigating) with fish emulsion with a bucket or sprayer, you can add liquid kelp to the same container and apply both at once. Liquid kelp can be applied to plants in the greenhouse, in pots, or in the ground.
- Where to get it: Most nurseries carry liquid kelp. You can also make your own with seaweed harvested from the beach.
- Learn more about liquid kelp.
10. Compost tea
- What it’s for: It allows you to apply nutrients from compost to the leaves of plants, which can make the nutrients more available to the plant and help suppress foliar disease.
- When to apply: You can apply compost tea as a foliar spray to plant leaves or to the soil around the plant root zone. It can be applied to plants in the greenhouse, in pots, or in the ground.
- Where to get it: You can make compost tea at home! Compost tea is made by steeping high quality compost in water and aerating it for a few days so it can “brew.”
- Learn more about how to make your own compost tea.
Organic Certified
Want to make sure you’re following organic growing practices with these amendments? Look for Organic Materials Review Institute (OMRI)-certified or California Department of Food & Agriculture (CDFA)-certified amendments. Products with one of these certifying labels indicate that the product is allowable in organic production. To learn more about the National Organic Program (NOP) and National List of Allowed and Prohibited Substances for certified organic operations, visit the USDA website.
However, just because it’s organic doesn’t mean it’s harmless; organic amendments can still cause damage to your garden and local ecosystems if used in excess. Take care not to over-apply any amendments, and follow the directions on the packaging or ask a trusted farming/gardening friend how much they recommend applying (often you can use less than recommended). Remember that improving soil health and nutrients takes time and attention.
Your soil doesn’t need to be perfect before you can begin planting either! Do what you can this season, start planting, and continue making adjustments over time. Keep clear records of what you applied, when, and what the results were. You can sample your soil again at the end of the season or the following year to see how your nutrients and pH have changed.
Learn More
Up Next: Biological Properties
Now that we’ve covered the physical properties of soil and the chemical properties, we’ll move on to the living part of soil that is key to healthy and regenerative soil: biological properties! Read the next article in the series here.
Want to go deeper? Our recommended resources and references are below.
You can also register for our Regenerating Watersheds & Soils weekend during our Permaculture Design Course. Dates and registration information is available on our website: santacruzpermaculture.com/permaculture-design-course/
Resources
Gershuny, Grace, and Joseph Smillie. The Soul of Soil: a Guide to Ecological Soil Management. 4th ed., Chelsea Green Publishing, 1999.
Gershuny, Grace. Start with the Soil: the Organic Gardeners Guide to Improving the Soil for Higher Yields, More Beautiful Flowers, and a Healthy, Easy-Care Garden. Rodale, 1993.
Hemenway, Toby. Gaia’s Garden: A Guide to Home-Scale Permaculture. 2nd ed., Chelsea Green Publishing, 2009.
Magdoff, Fred, and Harold Van Es. Building Soils for Better Crops: Sustainable Soil Management. 3rd ed., Sustainable Agriculture Research and Education Program, 2009.
Martin, Orin. “Your Soil—A Primer, with Some Strategies for Sustainable Management.” News & Notes of the UCSC Farm & Garden. Center for Agroecology & Sustainable Food Systems, University of California, Santa Cruz, 2011.
Miles, Albie, and Martha Brown. Teaching Organic Farming and Gardening: Resources for Instuctors. Center for Agroecology & Sustainable Food Systems, University of California, Santa Cruz, 2005.
“Soil Cultivation: Fundamental Concepts & Goals.” For the Gardener. Center for Agroecology & Sustainable Food Systems, University of California, Santa Cruz.