Soil is the foundation of good gardening. Without healthy soil, your plants will be more susceptible to pests and diseases and will, simply put, not perform well. When you start with good quality soil, you will reap the rewards in the garden.
Know Your Soil
Soil is much more than the dirt in your backyard. All soils are made up of minerals, organic matter, air and water that work together to provide the ideal conditions for plant roots to provide fuel for the plant to grow.
The mineral component of soil is a mixture of sand, silt and clay, and the ideal ratio is 40 percent each of sand and silt, and 20 percent clay. Too much sand and the soil can’t hold water, too much clay and the soil will be unworkable and retain too much water. When this ratio is out of balance, amending the soil with organic compost will improve drainage.
Determining the kind of soil you have is simple, you just begin with a soil test. Your local Cooperative Extension Service offers low-cost soil tests; you can also purchase soil test kits from the Garden Center. Select amendments for your soil based on the results.
Tip: A word about soil acidity and alkalinity: When gardeners mention pH, they’re really talking about nutrient availability in the soil. On the pH scale, 7 is neutral, and anything below is acidic. Above 7 is alkaline. Most plants will thrive in a pH range from 6.0 to 7.5, and that happens to be the pH of most commercial garden soils.
Of course, there are exceptions, like acid-loving blueberry bushes that prefer a pH around 5.5. Acidic soil can be amended with lime to make it more neutral or alkaline, while garden sulfur is added to alkaline soils to decrease the pH. Compost is neutral and will not affect the acidity of soil when added.
In addition to structure and minerals, soil texture is important to a healthy garden. The ideal loamy, friable soil holds together when you squeeze a handful. A sandy soil will fail to hold its shape when squeezed, and slightly damp clay soil clumps when squeezed. To achieve soil that is quick-draining but retentive, amend the soil with organic matter like compost and sphagnum peat moss.
The garden soil you purchase in bags or bulk from the Garden Center is designed to be mixed with the native soil in your garden. By adding garden soil and amendments, you can improve structure and revitalize tired soil.
Small space gardeners may shake their heads at the idea of “soilless potting mix,” but it’s the best thing you can do for container planting. It’s true, you can read the label on your bag of “potting soil” and it will show a mixture of ingredients like peat moss, pine bark, vermiculite, perlite and sand, but no dirt or soil. That’s because potting mix is engineered to be both well-draining and moisture-retentive to maintain consistent moisture and protect plants in between waterings.
Potting mixes also come with nutrient boosts. In the case of organic soils, nutrients like aged rice hulls, composted poultry manure, bat guano, worm castings, alfalfa meal, bone meal and kelp meal make up the ingredient list. Check package labels for more info.
If you want to make your potting mix, use the recipe that container gardening expert Jessica Walliser recommends: equal parts good quality garden soil and compost, either purchased or made in your backyard. Compost is easy to make at home, but requires time. Learn how to make your own compost.
How much should I buy?
There are a few variables in determining the amount of soil you will need to purchase. Begin by knowing the size garden space or container you will fill, and if you are adding an amendment such as compost. In the Garden Center, consult labels for quantities. You can also find the information in the online product listings.
For container plantings, count on one 32 quart bag of Miracle Gro Potting Mix to fill two 12 inch wide pots. Also, a 3 cubic foot bag of Kellogg Raised Bed and Potting Mix will fill approximately six 1-gallon containers. For a 50-gallon container, count on approximately eight and a half 3 cubic foot bags.
Soil Amendments and Compost
Besides garden soil and potting mix, you’ll want to use compost, “black gold,” in your garden. Compost improves any soil by enhancing drainage and providing nutrients as the material breaks down. Make your own or purchase it from the Garden Center and use it as you till the bed, plant the seedlings and even top dress mid-season.