Garden Soils

Understanding the soil in your garden is key to successful gardening.  The amount of available nutrients, along with the microbiological health of your soil, is key to healthy plant growth.  The websites below will help you understand the importance of the nutrient components, as well as the ability of your soil to retain water based on the  organic content. 

Most soils are derived from 3 common parent materials (rock types), these are igneous, sedimentary and metamorphic. Lastly there are organic soils, which are commonly called muck soils. More than 20% of the composition of these soils is organic matter, which is derived from cumulose (incomplete decomposition of plant matter due to settling in water).

Texture

This term refers to the soil constituents; sand, silt, and clay.  The percentage of each component in a soil determines it texture class. Loam, which is a great soil for sustainable agriculture is composed of all three constituent in roughly equal parts.

Clay dominates it's on soil texture class because of its very small size and strong negative charge.  Clay soils can have as little as 40% clay particles - and up to 60% sand or silt.

Sand is an inert material, meaning it does not retain nutrients or water. Sand is loosely packed with many large pore spaces, giving it good drainage. Sandy soils are generally dry and poor soils requiring frequent watering and fertilizing for plant growth. They can be amended with organic matter (OM) and clay to improve water and nutrient retention.

Structure

Mineral soil particles clump together forming aggregates, this in turn gives the soil it’s structure or tilth. There are pore spaces between the aggregates, ensuring movement of air and water through the soil.  Soil with good tilth will be approximately 50% pore space, half containing water and the other half containing air.  Pores are important because they allow water to enter the soil then drain away from the roots after a rain.  This drainage is important because it gives the roots the opportunity to respire (they use Oxygen and release Carbon dioxide), and take in water.  It also forces roots to grow in the direction of the water source, which is important for root crops such as carrots. 

Substances, such as Calcium and other positively charged minerals, help soil aggregate.  Other factors include plant root tips, organic matter, humus, microorganisms, and earthworms.  Humus, compost or other organic matter, will improve the structure, improve root growth, increase the microorganism population and attract earthworms.  

Soil Tilth 

Tilth is the physical structure of the soil, and it is strongly influenced by humified organic matter...for more on this topic, please link to Maintaining Soil Tilth and Fertility.

Metals in Your Soil
Controversy still exists about metal uptake by garden plants.  Here is some information from the Ministry of the Environment on how various metals can be taken up by different garden crops.  If you soil is contaminated, chances are you won't be able to grow vegetables on it anyways, but have your soil tested if you have any concerns.   The pH level of your soil is a good indicator of soil health, and should be tested regularly and neutralized with the addition of lime.

Ministry of Environment Factsheets on Metals in the Soil
If you are concerned about lead in your garden, please read the factsheets below.  Did you know that lettuce leaves can store seven times more lead than the roots of carrots. Beet leaves contain more lead than beet roots.

Arsenic
Cobalt
Copper
Lead
Nickel

Soil Websites
Soil Maps of Canada
Mycorrhizae and Soil Health
Soil and Nutrient Management
Soil Crust (website)
Soil Crust (document to download)

Adding Fertilizers
Which manure to use?