Soils 101: Soil Additives

Solving the Soil Equation

When faced with the question, “What should I add to my garden soil,” I typically respond, “There really isn’t a formula for doing that.” Wouldn’t it be nice if there was a tidy equation for amending the soil prior to each planting season? 

Was amending the soil even on your radar this spring? If not, that’s ok! It’s not required, but it can certainly improve your plant health and harvest yield. Maybe you’ve always thought of soil as a constant, unchanging part of the garden. It’s actually quite dynamic and plays a key role in plant health (i.e., it does more than hold plants in place). Let’s explore that a little more.

At any given time, the soil has a certain amount of available nutrients. These nutrients allow for plant growth and development (much like nutrients in the food we eat provide for human growth and development). If a plant is a pale green, or starts to turn yellow, it could be that it is nutrient deficient. The most efficient way to “feed” a plant is for it to take up nutrients through the roots. Since the roots absorb nutrients from the soil, it is important that we recognize when our nutrient levels in the soil might be low. I like to think of a fuel gauge. The soil, our fuel tank, may be full, empty, or somewhere in between for each nutrient a plant needs. Since our plants need several nutrients to thrive, our “dashboard” doesn’t just have one fuel gauge, but it looks more like an airplane with lots of gauges, each corresponding to a nutrient. 

The plants from last season pulled nutrients from the soil, so typically, plant growth “subtracts” nutrients from the soil. Young plants (like young children) need nutrients, so we want to “fill up the nutrient tanks” by “adding” nutrients prior to the next growing season. 

While a soil test can be useful, the level of detail it offers is more than required for most school gardens. Instead, I like to keep it simple with a 2-step plan.

1. Add organic fertilizer prior to planting. In many cases, this “addition” will feed your crops sufficiently for the entire growing season. We suggest selecting a complete organic fertilizer (fertilizer is identified by three numbers; look for a fertilizer where none of those numbers are “0”). The label will provide instructions for the appropriate rate and application method for your garden area.
2. Mulch your crops with compost throughout the season. This will increase soil fertility, help build organic matter in the soil, and support microbial growth.

In special cases, you may find it beneficial to make other soil “additions.” If your soil stays muddy and mucky without ever drying out, you might add a fine bark or perlite to improve drainage.Remember, your local office of the NC Cooperative Extension Service can assist you with any soil related issues or questions you may have. There are agents in every county who are familiar with your area’s soil, climate and other growing conditions. There may even be a Master Gardener’s group that will volunteer with the garden. Find your local office here.