Having a productive and sustainable vegetable garden starts with understanding the soil within which you are planning to grow your plants - I always think that 80% of gardening is about the soil, and only 20% is actually about the plants!
A range of simple soil tests can provide you with important insights into your soil's composition and condition and knowing this can help you adjust your gardening practices in ways that help you create the ideal conditions for your vegetables to thrive.
The following information describes the types of soil characteristics that I strive for and the tests that I do to help me develop my garden soil to produce an ideal growing environment for the vegetable plants in my garden.
The Importance of Soil Testing
Soil composition can vary from one place to another and can also change over time. Therefore, soil testing is important because it reveals the characteristics of your garden soil at that time.
Different plants have different pH and nutrient requirements, and without knowing your soil's current state, you may inadvertently harm your plants or fail to achieve optimal yields.
Soil tests that I use provide me with the following information:
pH Level
A plant's ability to absorb the nutrients they require is affected by the soil pH. If the soil pH is not within the plants limits of tolerance, it doesn’t matter how much nutrient you add to the soil, the plant simply won't be able to absorb it. So, pH affects nutrient availability to plants, not the presence of the nutrient.
Some vegetables prefer acidic soil, while others thrive in alkaline conditions. It is therefore necessary to be aware of your soil’s pH, what conditions affect it and what plants you want to grow in it.
Nutrient Content
Understanding nutrient levels helps you determine which fertilisers or amendments to use to ensure your vegetables receive the nutrients they need.
Soil Texture
Soil texture (sandy, loamy, or clayey) affects drainage and aeration. It also influences root growth and water retention.
Organic Matter
Organic matter includes all those plant based materials that ultimately break down and become a part of the soil. Within a gardening context, the most common forms of organic matter we add to a garden is compost and mulch. Ultimately, these form a part of the soil and improve its fertility, moisture retention and overall health.
Adjusting nutrients and organic matter can affect the pH, while adding compost will not only affect organic matter levels in the soil, but many nutrients and the pH as well. It is therefore important that you think about all of these soil characteristics holistically; you should not think of them in isolation.
Now, let's explore the specific types of soil tests for your vegetable garden.
pH Testing
Most vegetables prefer a slightly acidic to neutral pH range, somewhere between 6.0 and 7.0. While it is possible to send away soil samples to a soil testing service, I use a simple soil pH test kit. You will be able to purchase one of these from most good plant nurseries in your area.
Once you have your pH results, you can adjust your soil's pH accordingly using lime to raise it (for acidic soils) or sulfur to lower it (for alkaline soils). Ensuring that you regularly add compost to your garden will also help maintain suitable pH levels in your soil.
Soil Nutrient Testing
Nutrient testing provides insights into the levels of essential elements in your soil, such as nitrogen (N), phosphorus (P), and potassium (K), as well as secondary and micronutrients like calcium, magnesium, and iron. Low nutrient levels can lead to poor plant growth, so it's vital to understand your soil's nutrient profile.
You can conduct nutrient tests either through a professional lab or with DIY kits, but as with pH testing, I have always been very happy with the standard home gardener test kits that are readily available from many nurseries.
Based on the results, you can then customize your fertilizing strategy. For example, if your soil lacks phosphorus, you can apply a phosphorus-rich fertilizer before planting your vegetables.
Soil Texture Analysis
Many gardeners are not aware that plants must be able to use their roots to access oxygen from the soil. This enables them to produce the energy necessary for the absorption of many nutrients. It is therefore critical that the soil drains well and is well aerated. This is what soil texture is about and is determined by the proportions of sand, silt, and clay in your soil.
Most vegetables thrive in loamy soil, which is a balanced mixture of these three components. You can perform a simple soil texture test by creating a soil ribbon or conducting the jar test at home.
Organic Matter Assessment
Organic matter content is a key indicator of soil health. Higher organic matter levels improve soil structure, water retention, and nutrient availability. To assess organic matter, use the "feel and appearance" method, where you gauge organic matter content by observing the soil's texture, colour, and smell. Incorporating compost or organic amendments can increase organic matter content in your soil.
Interpreting Soil Test Results
Once you have your soil test results, interpreting them is crucial. Don’t be tempted to adjust levels by more than what is recommended on the packet/container. For example, if your test indicates that your soil potassium levels are down a bit; get some potassium rich organic fertiliser, and add as per the instructions (not more) - you can always add a little bit more later, but it is very difficult to remove it if you add too much.
Also, don’t be afraid to consult with some experts - take your results to a local nursery and ask for their advice. You can even post your questions with photos here on iCultivate.
Soil Testing FAQs
Soil testing helps you understand the nutrient composition of your soil, allowing you to make informed decisions about fertilising and amendments to promote plant health and optimal growth.
The frequency of soil testing depends on various factors such as the type of plants you are growing, soil composition, and local conditions. In general, I recommended to test your soil every 1 to 2 years.
Soil tests most commonly measure essential nutrients such as nitrogen, phosphorus, potassium, and pH. Micronutrients like iron, zinc, and manganese may also be included in some tests. Other sol tests will indicate what your soil texture is and the amount of organic matter it contains.
To collect a representative soil sample, use a clean shovel or soil probe to gather samples from multiple locations in your garden and mix them together in a clean container.
While home testing kits might not provide the same level of accuracy and detailed information as professional laboratory tests, test kits purchased from reputable plant nurseries will usually provide a level of accuracy that is suitable for the home vegetable gardener.
Soil pH measures the acidity or alkalinity of the soil. It's crucial because it influences a plants ability to absorb the nutrients that in the soil. Most vegetable plants prefer a slightly acidic to neutral pH range for optimal growth.
To raise pH, you can add materials like lime, and to lower pH, you can use elemental sulfur or acidic amendments. The amount needed depends on the current pH and the type of soil.
Yes, soil testing is important for container gardening as well. Container soils can become depleted of nutrients over time, and testing helps ensure that you are providing the necessary nutrients for your container plants.
Testing your soil and then using the information you gain to adjust the various components of your soil can help you to improve the health of your plants and increase your yields at harvest time. You do need to be patient, but the work involved will produce good results in the end.
