Outdoor Potting Soil

As you stand in the garden center of any hardware or big box store, you will see stacks and stacks of various sizes of packages of soil.  It can be extremely confusing but here are some tips that may help you.

Purpose

It actually makes a difference whether you are going to use the soil for a container planting, or in a vegetable plot, or to amend the soil in a landscape.  Some products are designed to retain water and others are not.

• Containers – Don’t use field soil. Go for a peat-based soil-less mixture.  This version is specially designed for season-long growth for annuals of moderate size.  In-ground plots need something different.  Peat-based mixes usually have some fertilizer included as a starter.  Of course, as the season progresses, you will need to refertilize appropriately.

At this point you are probably thinking about those old pots still filled with soil but whose plants have died.  Old potting soil has lost any fertilizer it once had and the older it is, the more likely it will not retain water.  You will need to re-mix if you want to use it again this year.

• Flower beds and raised beds – What you want in this case is to enrich your existing soil with natural material that will continue to break down over time while adding nutrients to make your plants grow well.

These are places where you should avoid products that contain peat.  Small amounts are okay, but nothing of any great consequence.  Field soil with compost is the first choice.

When you add this soil to your bed, make sure you incorporate it over the entire area, or as much as possible.  You want the plant roots to spread and if you only add it to the hole where you are going to put a new plant, the roots won’t venture any further and the plant probably will die.

If you will need a large volume, check with a local landscaping contractor or supplier or a rural co-op.  Sometimes you can get compost from a local municipal facility.

Components

Each bag has lots of different types of soil and additives.  Be sure you read the ingredients carefully and know the proportion or volume of each.  If this isn’t listed on the bag, you may want to consider another supplier.

• Major components –
  • Bark or composted forest products
  • Peat relates to the coarseness
  • Soil – This should always be sourced locally if at all possible. Different areas of the country and the world have different soil composition (clay, etc.) and have different degrees of acidity and alkalinity.  It should also be labeled as soil amendment not potting media.
  • Manure
  • Sand
  • Other waste-products – this can include coconut coir and wood fibers

• Minor components –
  • Perlite – These little white pellets will add aeration but not fertilization
  • Vermiculite – These are pieces of rock that have been expanded by heat and look shiny
  • Rice hulls – Also good to aerate the soil and can control weeds when used on the tops of containers.

• Specialty components –
  • Mycorrhizae – This is an organism that help the roots absorb nutrients and water. This is better for container gardening than field soil.
  • Fungicide – These would be specific to something that attacks the plant.

Manure and compost are good organic materials but be sure that the product does not contain herbicides.  This happens when the animal feces are scooped up with the hay or grass in the field that has been treated with an herbicide.

Most components are “natural” but will only be labeld as “organic” if they have been certified as such.  Many of the components in your soil mix are produced using organic practices but the manufacturer has not gone through the process (and expense) of the certification.

Mixing

To truly know what components are missing from your landscaping, you need a soil test.  We can deal with that in another article.  Once you know what you actually need to make the soil the correct pH for the plants you are growing, you will know what to add.

• Lime – Many soil-less mixtures are have a low pH, or are acidic. If you are trying to bring your soil to neutral and you already have an acidic soil, you will need to incorporate lime.  Or, if you have an alkaline soil, go with sulfur.
• Fertilization – As previously mentioned, most potting soils have a starter of fertilizer. After a few weeks, use a water-based fertilizer or a long-term, slow-release product.  Short-term fertilizers will last for three or four months, but if the summer is hot, this will get used up quickly.
• Watering – Containers will dry out more quickly than an in-ground bed, so monitor carefully.

Here we are…back to the beginning where you are staring at the array of packages of soil.  When you know what you need for your application you will be able to find the products that are similar and purchase based on your budget.