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What are 'soil amendments'?

Improving Garden Soil

Tracy DiSabato-Aust (Garden Designer and Author) gives expert video advice on: What are 'soil amendments'?; What is the difference between 'organic' and 'inorganic' soil amendments?; What is 'leaf humus'? and more...

What are 'soil amendments'?

These are usually additives that are put into the soil to improve drainage and to increase the nutrient-holding capacity. They can be organic or inorganic.

What is the difference between 'organic' and 'inorganic' soil amendments?

Organic soil amendments are derived from living things. Examples would be composted leaf humus, composted bio solids, or sphagnum peat moss. Inorganic would be items like sand, pearlite, some people even use shredded tires.

What is 'leaf humus'?

Leaf humus is basically composted leaves. It's high organic, usually nutrient-providing. Whether it's acidic or alkaline will depend on the type of tree that the leaves came from. Leaf humus is beneficial for both sandy as well as clay soils. It will improve the drainage in clay soils and will provide nutrients and improve nutrient-holding capacity in sandy soils.

What is 'sphagnum peat moss'?

Sphagnum peat moss is an organic soil mimic that is basically non nutrient providing, but is used to improve aeration or drainage in clay soils. It's not to be confused with the black muck peat that is so far in it's degradation in composition that it does very little to improve the soil structure.

What is 'composted biosolids'?

Composted bio solids refer to a mini-cocktail party - composted sewage sludge and it is actually very high in nutrients. It's highly regulated and it's useful for many soil types as far as providing nutrients.

What is 'composted manure'?

It is manure that has gone through a composting process, and is in a nutrient form that's usable to plants. And there can be horse, cow or chicken manure, being the highest in nutrients. So not all poo is created equal.

What is 'compost'?

Compost is really used as a catch-all term for any organic material that has gone through this composting process. It can be yard waste - that is usually what we refer to compost - but it can be leaf humus, and composted bio-solids are referred to as compost. So it can be a variety of different materials.

What is 'topsoil'?

Topsoil is basically the top two inches of soil that is scraped off the land, and unfortunately topsoil is not very highly regulated so soil can continually be scraped off and that would be the top two inches for that area. It can be very low in nutrients and normally it is, so that's a mistake often gardeners make - they feel they bring in a load of topsoil, but this topsoil may have very few nutrients and it may do very little to actually improve the soil structure that we're working with.

What is 'gypsum'?

Gypsum is calcium sulphate, and it's often sold to be used in clay soils. However, in most clay soils in the Midwest and the East, it does very little to improve the drainage or the soil structure. It can be used on soils that are high on salt content in the Western states, and it's effective as a soil amendment to improve the structure of the soil there.

What are soil 'aggregates'?

Soil aggregates would be things like pea gravel. We also use Chicken Grit even, as an aggregate. And I will use aggregates ( gravel, grit) in my heavy clay soil that's poorly drained, when I want to try to grow a plant that requires better drainage. You need to actually line the hole with the grit and plant the plant, and then actually even use it as a little bit of a mulch to help keep moisture away from the crowns.

What is the best organic soil amendment for my garden?

Well, I hesitate to give a blanket answer on that because it's really very much dependent on where you garden, what amendments might be available to you. Therefore this is really where we want to look at a soil test, to see what type of soil structure we're already dealing with. Because many times people will think, 'I'm going to add sand to my soil' but if you have a clay soil and add just a little bit of sand you'll actually create concrete. So it's really important to know what type of soil you have, what amendments are available to you, and select from there.

How much organic matter should I add to my garden?

A general rule of thumb that I like to do, based on a soil test to see where your organic matter content is, is that you can test for that, but normally we're adding about 4 inches of organic matter content. We usually start with disturbed urban soil, which is about 2% organic matter. Most plants, particularly herbaceous plants, require at least 6% organic matter content.

Why is it important to follow the application instructions for organic soil amendments?

Well, there is the possibility to use too much, and it's the law of diminishing returns. If we add too much organic matter content, we can actually decrease the drainage of the soil. We would end up with a very spongy, heavy soil. So it's important to understand, again, what kind of soil structure we're starting with, and how much we can add, so that we're not adding too much and we're really kind of defeating the whole purpose.