A healthy soil is the foundation to a healthy garden. Harris Ivens, MSc, shared some of his wisdom with us at our last “Ask a Master Gardener” on April 30, 2020. Here are the key points:

Soil and compost

Soil is complex. It has chemical, physical and biological properties. Soil (the pedosphere)  is made up of elements from the biosphere (living organisms),  the atmosphere (gas exchange), the hydrosphere (water exchange) and the lithosphere (rock and mineral basis).

Soil, by definition, contains minerals like sand or clay and organic matter like decomposed plant litter. Compost is the “soup” of the soil. Plants “eat” this soup; so the “yummier the soup” the better the plants grow.

Our soil in the Kingston area tends to be clay based and this is good because:

  • The particles have a large surface area for “transacting” with the various elements in the soil.
  • Clay has a high nutrient holding capacity so can hold more minerals, like potassium and magnesium, compared with sandy soil (this is known as the cation exchange capacity (CEC)
  • Clay has a high water holding capacity, compared with sandy soils.

However, when you add compost to a clay soil, it allows for better development of a healthy diversity of elements in the soil and facilitates  exchange of these elements for the health of the plant. The biological creatures on the soil surface are the “work horses” moving soil and other elements. For example, mites bring dew down into the soil each night. Compost aids in developing a balance between microbial activity in the soil and the minerals added to the soil.

All exchange activity in the soil takes place on a microscopic level. When a plant is pulled out of the soil, only the “larger” parts of the root system are exposed. What’s left in the soil are the finer roots, where all the “action” happens.  There are many ways to compost and this is an easy one:

Compost recipe

4 parts brown material (carbon)

1 part green material (nitrogen)

½ to 1 bucket of soil (contains clay)

Lots of water (50% – when squeezed, a drop or two of water will seep out)

Batch Method:

  • Combine all “ingredients”. There are many ways to do this: layering in a 1 cubic meter pile or in a cone shape about 1.5 meter round at the bottom. The key is to get as much surface area of all materials as possible exposed and in contact with all other material. Harris runs his garden hose continuously as he builds his pile.
  • Leave to decompose.
  • If you want to speed up the process, turn the pile once or twice. After turning you could have compost available for use in 6 – 8 weeks. The speed of decomposition depends on the types and proportions of green and brown materials you have in your pile.
  • Compost is ready to use when it looks and smells like soil – you should not see original pieces of the ingredients and there might be a lot of worms!

The aim of making compost is to grow the biology (soil microbes) in the garden.

Note that there’s no perfect way so, experiment and have fun. It’s nature’s fertilizer!

Compost and general garden maintenance

Add ¼ inch of compost each year to your soil surfaces. If you give the earthworms a little time they’ll come up and eat it. They’ll work for you to “mix in“ the compost.

Why add soil to compost?

  • Soil contains a huge mineral base that is in a slow release form for plants to use when they need it:

Our region’s clay soil is full of calcium and magnesium which provides an excellent base for our compost. These elements come from the limestone and glaciations in the area. Our soil also provides a free source of potassium and phosphate. Many of these elements are found in the top three feet of our garden soils.

  • Soil makes the compost pile easier to manage:

Soil decreases the amount of heat in the compost pile. If there’s no soil, more water must be added and the compost pile needs to be turned more frequently to prevent excess heat. If the pile gets too hot, nutrients are lost. Note,  heat is an important factor if killing weed seeds  is of concern.

  • Clay soil holds moisture
  • Soil provides biological inoculation

The digested excretions and decay of soil organisms leads to the increase in the diversity of nutrients in the soil.  This inoculates the soil. (Commercial inoculants also have their place; they tend to be more targeted)

  • Soil captures carbon
  • Soil is free.

In Harris’s experience, adding soil results in more compost being created. He believes the soil changes the composition of microbes, reducing those that consume and expire carbon.

What type of soil should be added?

Any soil with living organic matter will work.

  • Forest soil will add diversity to your compost pile. Garden soil tends to be rich in bacteria while forest soil tends to be rich in fungal elements.
  • Weed free garden soil will prevent having weeds in your compost.
  • Clay soil has good water holding capacity, but can be heavy to mix in. Ideally, first mix clay with water in a bucket. This slurry can then be mixed into your compost allowing a thin layer to wrap around the organic particles. 

How to keep racoons, and other critters out of your compost?

Aim to make your compost pile as hard to get at as possible. Harris has built a 4 to 5 ft compost area with deer fence to protect his compost from racoons. He added chicken wire at the bottom to prevent the racoons from reaching in. Other options are to mix in more brown material and/or keep the brown material on the outside of the pile and the green material in the middle. If you choose to bury your compost in the soil, spread it out and bury it as deeply as possible to discourage raids from hungry critters. You can also  cover this area with chicken wire for the first few weeks and remove once the smell is gone. Remember that racoons and other creatures have a role to play in our ecosystem. They add scatt and help till the garden.

What are greens?

Kitchen scraps like vegetable peelings are greens. Generally, the more slimy the scraps are, the more nitrogenous they will be and you’ll need to add less to your compost. The more fibrous the scraps are, the less nitrogen they will have. In composting, the aim is to balance the carbon to nitrogen ratio (C:N). Green material is high in nitrogen, browns like cardboard and dead or dry plant material are carbon.

Some interesting nitrogen ratios: fresh leaves are 20 to 50 carbon molecules to 1 nitrogen molecule. The ratio of chlorophyll to nitrogen is 1 : 4. Nitrogen is also found in proteins and in leaf sap, the “blood” of the plant.

Carbon is involved in the structure of the plant. It forms  the backbone of proteins and is also found in liquid form in plant cell walls (sugars).

An interesting note: comfrey is one of the first plants that comes up in the spring and is very leafy. These leaves can be cut, dried in the sun and stored in a dry place for use later as green material. In general, older leaves are more fibrous (as opposed to juicy), therefore, tend to have more carbon. Younger leaves are more supple, slimy and easy to squeeze and tend to have more nitrogen.

Is it good to add coffee grounds to compost?

To determine the C:N ratio of any ingredient you add to your compost, consult any online table or check this one for coffee grounds: http://compost.css.cornell.edu/chemistry.html

Will adding moldy waste be problematic to your compost?

No, as there are many other microorganisms in compost which will help regulate the balance.

Should you add wood ash to compost?

Add very sparingly (sprinkle lightly). Wood ash isn’t high in carbon but is very alkaline. Adding alkaline material can be harmful to microbes in the pile.

Should you add sawdust?

It depends on the type of wood from which the sawdust came from. Consult a carbon to nitrogen table. Note that sawdust tends to mat and block air flow and can encourage harmful anaerobes – your compost pile should always be aerobic. It also takes a long time to decompose.

What to do if you are low in browns?

Use more soil. A disadvantage of using soil is that the pile will become heavier to turn and can get too dense. To monitor, put a stick into the center of the pile, pull it out and smell the end. If it smells bad the pile should be turned, and if you can add cardboard for carbon.

A fun way to make compost?

Try vermicomposting. Special red wiggler worms do the work indoors and they make VERY nutritious compost. Here’s a good source: https://www.cathyscomposters.com/worms.htm

Join us tomorrow

If you’d like to learn more from Janette Haase, register for her Monday afternoon coaching sessions on Zoom.

If you’re not already registered, join our next Master Gardener Zoom Q & A on Eventbrite

Thought for the day:

Grow it….Don’t mow it 😊

And plant vegetables instead of flowers this year.

Happy gardening!

Reporting by Colette McKinnon, Master Gardener in Training, Rideau 1000 Island Master Gardeners