Potting Soil is There a Difference?

Soon it will be time to start planting seeds. Different seeds need different light and water requirements but what about starting soil?

Premixed potting soils actually don’t contain any soil! These sterile mixes are made up of a combination of ingredients that each serve a purpose.
Composition:
Most mixes contain one-third peat, one third volcanic ash and one-third compost.
• Peat moss or sphagnum moss helps hold moisture in place. Too much peat makes the soil too light and water runs off and doesn’t absorb. Absorption is important so the water is there when the plant need a drink. Coir fiber made from coconut shells is a good renewable alternative source for water retention. Look for coir in the ingredients in organic mixes.
• Volcanic ash also known as perlite and vermiculite serve as diversions for beads of water. These ashes are added so water doesn’t pool at the bottom of the flower pot. It helps keep water suspended in the mix.
• Compost is added to give the mix texture. Compost also adds nutrients to the mix.
The most important thing you need is good drainage. Seedlings and tender transplants can’t tolerate “wet feet”. Dampening off and powdery mildew are popular plant killers from too wet soil.
Most potting soils are sterile mixes. If you would rather use garden soil, you need to sterilize it. Place soil in a layer about 1-inch deep on a cookie sheet (use this sheet for soil only). Bake at 200 degrees for 2 hours. Warning: it does NOT smell pretty.

I know how important soil organisms are to plant health. Soil is alive. So why am I telling you to kill it?

Starting with sterile soil helps curb bad bacteria and insects from harming tender seedlings. You can add fertilizer as needed to your plant as it grows. You can also buy plant specific potting soils for plants like African Violets and succulents like cactus.
Another alternative mix is organic mix. This mix contains coir and compost with guano (bat droppings) and chicken manure. It makes a great starter soil.
Now that you know the difference in potting mixes let’s start planting!
Have a gardening question? Send it to me at and I’ll answer it in an upcoming column.
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