The calendar shows it’s spring. The longer days definitely say “spring.” And the weather couldn’t be more “spring-like.” But I’m concerned about the soil in my small garden. Besides battling the gophers (what could they be finding to munch on down there?), my soil is dense and I need to make it more fertile. Here’s what I’m going to do to solve that problem.
Soil is an ecosystem made up of the living or that which was once alive and the abiotic, which is made up of minerals, air and water. Soil texture is determined by the percentage of sand, silt and clay in the soil. Sandy soils are usually low nutrient, drain well, warm quickly and allow early cultivation and planting in the spring. Clay soils are the opposite.
Some soils are more beautiful than others, but any soil can be radically improved with the addition of organic matter.
We live on ancient sea cliffs. Soils in Bonny Doon and Scotts Valley consist of shallow, excessively drained weathered sandstone and shale. Felton soils were formed from shale, sandstone or mica schist. Those in Ben Lomond and Boulder Creek had their beginnings from weathered sandstone or granite. Although these provide the necessary mineral component of our soil, organic matter or humus from decayed plant and animal material are necessary for fertility.
Here’s why improving your soil will make a difference to the health of your plants.
Good soil—with both organic matter and minerals—helps plants grow by forming the food supply for soil bacteria that help make food available for plant growth. Most of a plant’s energy goes to producing substances that drip out through the roots to attract bacteria and fungi. These in turn attract good nematodes and protozoa to the root zone. The protozoa eat bacteria and the nematodes eat not only the bacteria but also fungi and other nematodes to get carbon. What they don’t need they expel and this feeds the roots, much like earthworm castings.
Down in the soil, if a plant needs different foods, it can change what it secretes. Different substances will attract different bacteria, fungi, nematodes and protozoa. This huge diversity of soil biota helps the good guys keep the bad guys in check.
A common way to destroy the microbiology of the soil is to add salts in the form of non-organic fertilizers. The salts kill the bacteria and fungi by dehydrating them. Then the plant can’t feed itself and becomes dependent on its fertilizer fix. Without the good bacteria and fungi in the soil other parts of the food chain start dying off as well.
The soil food web is also responsible for soil structure. Bacteria create slime that glue soil particles together. Fungi weave threads to create larger soil particles. Worms and insects distribute bacteria and fungal spores throughout the soil and create pathways for air and water.
What can you do to bring your soil back to life?
- Mulch around perennials, shrubs and trees with 1/4“ of compost and 2-3” wood chips or other organic mulch.
- Apply mycorrhizal fungi, especially in a new garden that’s been rototilled or chemically fertilized. You can find this in most organic fertilizers and some organic potting soils.
- Use aerated compost tea.
- Try to avoid walking on the root zone of plants. This kills fungi in the soil. Install stepping stones to preserve soil structure.
Jan Nelson, a landscape designer and California-certified nursery professional, will answer questions about gardening in the Santa Cruz Mountains. Email her at [email protected], or visit jannelsonlandscapedesign.com.
