How to Build and Nourish Healthy Garden Soil
The most fundamental element of any garden plays a vital role in your success.Posted Mar 14, 2017
Peer into a healthy garden bed and you will see much more than tiny grains. Soil is more than particulates of peat, sand and clay. Healthy, vital soil is a complex combination of medium, minerals, air, microbes, fungi, and other life that all contribute to a plant’s ability to access nutrients and retain the moisture necessary to grow.
Thankfully, improving your soil doesn’t have to be complicated. In fact, if you can create the right environment with a few simple additions, the life in the soil will actually do the work for you.
Healthy Garden Soil Tip #1: Begin With Soil Structure
To begin addressing your soil needs, you first need to look at soil structure. This includes the physical aspects of the medium you’re working with and the varying ratios of sand, clay and organic matter. That last one—organic matter—is the most fundamental element in any garden. Whether you’re adding it to a sandy soil, clay, or existing loam, it will play the most vital role in improving your soil’s quality.
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That’s because organic matter is where life happens in the soil. Fungi, insects, molluscs, mites, and worms all work collectively, transforming minute particles of plant waste into a nutrient rich, healthy medium for plants to grow in. The plant waste can come from peat moss, mulches of grass clippings or shredded leaves, or compost. As the material gets watered into the soil, it slips down between sand and clay, providing aeration in dense soils, increased water retention in sandy soils, and overall improvements to the nutrient availability of any soil.
Benefits of organic matter
- High moisture retaining capacity: Well composted organic matter can hold up to 90% of it’s weight in water.
- Improved cation exchange: Cation exchange capacity or CEC is the number of cations a soil can exchange at a given pH. Essentially, CEC is what determines which nutrients are available to your plants and is measured as soil fertility. Organic matter has three times the cation exchange capacity of the richest clay.
- Aeration in dense soils: Healthy soil, like any other living organism, needs airflow to thrive. Without sufficient airflow, plant roots and beneficial organisms cannot access the necessary oxygen required for growth. Additionally, carbon dioxide can build up in the soil atmosphere and plants will stunt, ceasing to grow.
- Important nutrients: Decomposing organic matter provides the soil with nutrients that plants need to grow. Fungi, invertebrates, and microorganisms break down organic matter, converting it into the simplest forms of micro/macro nutrients, such as nitrogen, phosphorus and potassium.
This is why you should replenish the organic matter in your garden as it succumbs to wind and water erosion over the seasons. In the wild, falling leaves, dying grasses, and local bugs and animals naturally replace organic matter in the soil. This is the natural cycle of a woodland or meadow breaking down at the end of the season. It’s also what we should try to mimic in our garden maintenance programs.
How Do You Know if Your Soil Needs Organic Matter?
In order to calculate how much organic matter you need to add to your garden, you first need to determine what kind of soil you have.
|Loam Soil||40% sand, 40% organic matter, 20% clay. Ideal garden soil.|
|Clay Soil||Clay minerals, metal oxides, and little organic matter. Rich in nutrients but hard and compact when dry.|
|Sandy Soil||Usually small rocks and minerals, very porous. Plants quickly dry out.|
Perform the soil squeeze test
If you don’t know what type of soil you’re dealing with, take a handful of moist (but not wet) soil from your garden and squeeze it in your hand.
- If it retains its shape and crumbles with a poke, you have loamy soil. Lucky you! Your yearly maintenance will be minimal, requiring small additions of organic nutrients in the form of well-rotted compost every spring.
- If it retains its shape and does not break with a poke, you have clay soil. Unfortunately, this soil needs work. Till or work your soil until the medium is quite loose. Compaction is the biggest enemy in clay soils, so avoid stepping on beds and add generous amounts of fine organic matter in the spring and fall. Top dress with larger, mulch-like clippings, sawdust, or fine chips. These will break down slowly and work their way into the soil. Clay soil is usually very rich in nutrients, so avoid fertilization unless a soil test demands it.
- If it crumbles when you open your hand, you have a sandy soil. This is the most common and the easiest soil to amend. On its own, sandy soil drains so quickly it can be hard to keep up with the watering. This is because sand particles are large and coarse, which allows water to move through it very quickly, causing plants to wilt soon after a rainfall. Sand has no capacity to retain water without the help of lots of organic matter and a bit of clay. Over time, and with regular additions, you can turn sandy soil into a nice rich loam.
Healthy Garden Soil Tip #2: Understand Soil pH
One thing to understand when physically building your soil is that your plants’ access to soil nutrients depends upon soil structure and pH. For example, your soil could be rich with nutrition, but if the pH is out of range, your plants can’t access much of it.
Soil pH is the measurable level of acidity or alkalinity of the soil medium. The measurable range is between 1 and 14, with 1 being highly acidic and 14 being highly alkaline. Plant nutrients are only available at a certain pH and can become unavailable when pH is too far from the ideal range, as in the case of iron being “locked out” in alkaline soils.
Ideally a vegetable bed should be on the slightly acidic side of 6.5 to access the nutrients required for the majority of crops. For landscape plants such as forsythia, wiegelia, lilac, and boxwood, you want a soil that is more alkaline—with a pH of 7.5.
You can change the pH in your garden bed with a few amendments, but not before you do an accurate soil test to determine what you need. Adding lime will sweeten the soil up, bringing it from acidic towards alkaline, whereas sulfur will acidify the soil for plants like rhododendrons and camellias. Over-applying either of these amendments can cause harm and under-applying would be a waste, which is why a soil test is necessary. Testing your soil is worth repeating every spring.
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For a more detailed list of soil amendments that will help you improve your soil’s structure and pH, see the table below. To understand fertilizers and how to add them to your garden, you can find a detailed article here
|Soil Amendment||Purpose and Effect|
|Compost||The most valuable amendment. Adds rich organic matter to the soil.|
|Manure||Adds rich organic matter but may contain weed seeds.|
|Peat||Raises soil acidity, increases aeration, and improves moisture retention. A limited resource.|
|Coir||Conserves water, improves soil structure, and helps plants retain nutrients. An abundant, renewable resource.|
|Grass clippings||Helps condition and aerate the soil when used as mulch, adding organic matter as it breaks down. Be careful of the source: some grass clipping may contain chemical pesticides.|
|Fall leaves||Excellent as mulch. Adds organic matter as it breaks down, helping to aerate the soil and increase moisture retention.|
|Wood shavings/chips||Add as mulch to the top layer of soil. Best for clay soils that needs conditioning. Add grass clippings or manure beneath to facilitate decomposition.|
|Green manure crops||Help lighten and enrich the soil, adding nutrients and organic matter. Can also help break up clay soils.|
|Lime||Increases the alkalinity of your soil. Will help create crumb structure in clay soils.|
|Wood ash||Will increase pH of soils, add potassium and calcium, and help improve soil structure in clay soils.|
Recognizing that soil is a living component of your garden and that it needs to be nurtured and cared for will lead to healthier plants and tastier crops. And everyone benefits from that outcome.
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Jessica Dawe owns a garden center and has been practicing integrated pest management and permaculture since graduating in 1995 with a degree in horticulture.