Add fertilizers
Fertilizers are products that add plant nutrients directly to the soil. Whether growing plants in a garden bed or in soil containers, we recommend adding natural and organic fertilizers to get plenty of natural plant nutrients into your soil. Here are just some of the natural fertilizers commonly available that you can use to get started.
Minerals and rock powders
- Greensand – This product forms as a sediment in shallow seas and is a good source of potassium, iron, and silica.
- Azomite – This is a volcanic deposit that is mined from an ancient sea bed in Utah. It contains 70 different trace minerals and is a good source for some rare plant nutrients.
- Gypsum – Gypsum is a naturally occurring Calcium Sulfate mineral. Calcium and sulfur are both essential plant nutrients and this is a good way to supply them, especially if your soil pH is high (alkaline).
- Lime – Calcium and/or Magnesium Carbonate (dolomitic lime) is also an excellent source of calcium and magnesium if your pH is low (acidic). Applying lime can bring the soil pH back up into an ideal range.
- Rock phosphate – This product is mined from phosphorous rich clay deposits and is an excellent fertilizer to use if your soil is deficient in phosphorous. This nutrient is especially important for plants to grow strong roots and blooms.
Organic and animal waste fertilizers
- Bat guano – There are several different types of bat guano (bat poop). Depending on how and where it is collected, it can be high in either Nitrogen or Phosphorous. In addition to adding these nutrients, bat guano is exceptionally good at stimulating microbial activity and is a great ingredient for compost tea.
- Seabird guano – Similar to bat guano, seabird guano is the waste of seabirds that eat fish and is often high in Nitrogen and Phosphorous. This product can be used the same way as bat guano, but tends to be a little stronger so be sure not to apply too much.
- Kelp meal – This product is made from seaweed and is a great, mild source of Nitrogen, Phosphorous, and Potassium as well as some trace minerals. You can almost never go wrong adding some of this to your soil.
- Fish meal – Pretty much what it sounds like, fish meal is ground up fish parts. This product is an excellent, natural way to add a lot of different nutrients to your soil. It is particularly high in Nitrogen, but usually contains Phosphorous and Potassium as well as many different micronutrients and amino acids.
Each of these products adds a different plant nutrient or series of nutrients and it is important to choose the ones your soil needs based on a soil test (see “choosing a location“) and apply them at the correct rate as directed by the manufacturer. For our Colorado soil, we like to add greensand, gypsum, and bat/seabird guano to get plenty of iron, calcium, and phosphorous. We also like to add kelp meal and fish meal occasionally when planting new transplants.
The term “soil amendment” refers to any material which improves the soil physically or chemically in order to make it more suitable for plant growth. Amend with compost
When deciding what products to add to the soil of a new garden, organic matter is always the first thing to consider. Adding compost to your soil is usually the best first step, especially when making a new garden from a lawn or old garden bed. Adding large amounts of compost changes the physical and chemical properties of your soil, providing a healthy environment and food source for all of the beneficial microbes that break down soil minerals into plant nutrients. These cultures lower the soil’s pH value, making nutrients in the soil more available to your plants and improve the texture and drainage of your soil. A healthy soil will not only contain all essential plant nutrients in abundance, but will maintain an environment that makes them available to the plants that are growing in that soil. We recommend applying a good 3 inch layer of compost to your garden soil each year and digging or tilling to mix it as deeply as possible into your garden bed.
In this picture, you can see our red and green lettuce, dinosaur kale, and young tomato plants thriving in our acidified soil with plenty of compost. To calculate how much compost you need to apply a 3 inch layer, take the surface area of your garden in square feet and divide by 4. This will tell you how many cubic feet of compost you need.
Example: For a bed that is 8 feet long and 4 feet wide, the surface area is 32 square feet. 32 divided by 4 is 8 so we would buy 8 cubic feet of compost to add a 3 inch layer.
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