Understand Your Soil
What’s in your soil?
Soil is made up of minerals, air and water, and organic matter.
- Mineral particles (the “dirt”) come in different sizes.
- Tiny clay or silt particles pack tightly: they can hold a lot of nutrients, but it’s hard for air and water to penetrate.
- Larger sand particles let air and water in, but can’t hold much water or nutrients for plants.
- Air and water: about half the volume of a healthy soil is pore spaces made by soil life that provide aeration, water-holding capacity, and room for roots to grow.
- Organic matter is all the billions of soil organisms plus the dead decaying plant matter that supports them. This soil life and organic matter create soil structure, hold moisture, protect plants from disease, and store and recycle nutrients for healthy plant growth.
Fixing soil problems – dig in and take a look!
If plants aren’t growing well, the problem is often in the soil. Slice and lift a shovel-width of soil to find these common problems, and solutions below.
- Light-colored sandy or gravely soil, indicates low organic content. Mix 3 inches of compost into the upper 6-8 inches of the soil, and replant. On lawns, aerate and rake in ½ inch of compost. Around existing trees and perennials spread 1-2 inches of compost – the worms will work it into the soil.
- Gray, sticky soil indicates clay. The same compost applications will “open up” clay soils so air and water can enter. Use a little less compost when amending clay soils – about 2 inches of compost mixed into the upper 6-8 inches of soil.
- Yellow, gray, blue, or black heavy soil, sometimes bad-smelling, indicates poor drainage so that air can’t enter. These saturated soils may require installation of subsurface drainage. Or you can change to plantings that don’t mind “wet feet” (ask the Garden Hotline for plant recommendations). Build up raised planting beds for plants that need better drainage.
- Hard, compacted soil, may be caused by low organic matter (add compost), heavy traffic, or overuse of chemicals like “weed and feed”. Aerate and/or till in compost.
- Few worms or other soil creatures can be a result of overuse of pesticides and soluble fertilizers. Reducing chemical use and adding compost will bring soil back to life.
- Thatch build up (thatch is brown fibrous old stems in lawns) of more than ½ inch may be caused by overwatering, over-fertilizing, and incorrect mowing height. Aeration or de-thatching and changing practices will reduce thatch build up.
- Shallow roots (less than 3” deep in lawns) are caused by watering too frequently and soil compaction. Aeration, compost topdressing, and watering deeply but less frequently all encourage deeper root growth.
Questions? Call the Garden Hotline at (206) 633-0224 or email firstname.lastname@example.org