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Module 14: How to Improve your Soil Type

One of the key parts of gardening and starting your own garden is identifying and improving soil types. That’s not to say that if you have one soil type, you can only have plants that naturally do well in those soils. However, it does help to work with what you’ve got. This is why we have devised this course, to help you improve your own soil rather than relying on pots and containers to grow your plants. However, those are also good options if you have naturally infertile soil. 

Improving your soil types

Lesson Objectives

  • Identify your soil type
  • Execute an at-home pH test
  • Learn how to improve different soil types

Identifying your Soil Type

Different soil types

Identifying the soil type in your garden is the first step to improving what is already there. We have created a guide on identifying your soil type previously in this course. So please refer back to this for further information. Though the main soil types that you may come across in your garden are as follows:

  • Loam – these soils are a well-balanced blend of sand, silt and clay (generally 40-40-20)
  • Clay – these soils have heavy clay particles which compact when wet and under pressure and often retain too much water
  • Sand – these soils have sand particles which are often very acidic but do not retain moisture very well
  • Silt – these soils contain particles which are somewhere between clay and sand in terms of size. Silt is rich in minerals but breaks down more easily. These soils are often used in farmlands due to how fertile they are. 
  • Chalk – these soils are quite alkaline and contain chunks of chalk or limestone. Water drains through these soils quite quickly – they are not good for water retention. 

Activity: Determine your soil type. Refer to module 3, where we detailed how to perform a soil-type test.


pH Testing

Testing soil sample ph value

Testing the pH of your soil is helpful if you want to improve your soil and get ready for planting. The pH scale ranges from acidic to alkaline. A pH of 1 is very acidic and 14 is very alkaline. The reading would be around 6-7 for a neutral soil pH. Most plants will generally prefer neutral soil. However, some are acid-loving and some have a preference for alkaline soils. Some plants, most notably hydrangeas, will even change the colour of their blooms depending on the pH of their soil. 

Ways to test soil pH

There are a couple of options when you need to pH test the soil. You can either request that a professional test the soil – you can receive much more conclusive results this way about the soil’s nutrients and pH. Or, you can purchase at-home test kits. These test kits will usually have a litmus paper indicating the soil’s pH by the colour it changes to when testing. The first step is to mix some soil with room-temperature distilled water and then dip the litmus paper for 20-30 seconds before comparing the test paper to the kit’s key. These keys will usually have a scale, with the colours ranging from red (acidic) to purple (alkaline.)

Once identifying the soil pH, you can use additives to neutralise or increase the soil’s pH levels. After using any additives, testing the soil again is a good idea. Just to make sure that the additives have had the desired effect.

Activity: Determine your soil type. Refer to module 3, where we detailed how to perform a soil pH test.


Improving your Soil

After determining which soil type and testing the pH, you can begin to improve your soil. This is generally done by adding manure or other organic matter. As well as mulching and using a feed or other nutrient additives. It is always best to plan which plants you want to incorporate before improving the soil. You may find that some plants will already thrive in your soil. Whereas, other plants may require additional improvements than others. Another thing to consider is the aeration and drainage of the soil. Even plants that thrive in some soils may need some help with drainage to keep them happy and healthy. 

Improving Clay Soils

Clay soils will compact quite densely if allowed, as their particles are heavy and malleable – pressure and moisture will compact the soil and make it difficult for plants to find adequate drainage. This can lead to root rot and other issues. Gravel or grit – coarse grit rather than fine grit – can help to break up the clay soils, though you will need quite a lot to make a difference. Digging in this gravel or grit can help to improve the soil structure, though stay away from too fine grit and stay away from sand altogether, particularly when dealing with heavy clay soils as these can make the clay even harder to work with.

If you do have particularly heavy clay soils then sticking to organic matter is usually the way forward as these will help to prevent the soil surface from drying out or cracking in the heat – if it is too difficult to work with then raised beds may be easier. This organic matter can be used as a mulch around the plants and will help with nutrients as well as stop the soil from drying out. 

Improving Silt Soils

Silt soils are somewhere between sand and clay, meaning that they can compact well but also have relatively adequate drainage. Unfortunately, they can also erode quite easily. These soils are used a lot in farmlands as they have a high mineral content generally however, they do not usually have much organic matter. As such, it can be very beneficial to fork in organic matter or spread it over the soil surface. The best times to do this are either in the spring or autumn. If you choose to spread the organic matter over the top of the soil, a 5-10cm layer is recommended.

One of the best ways to avoid soil compaction is to till the soil and disperse the organic matter throughout the silty soil evenly. Raised beds are also something to consider as they are easier to work with if the soil appears to be particularly problematic – the raised beds would help deter any issues with erosion, etc., in the rain as they will be more closely contained and manageable. 

Improving Sandy Soils

Sandy soils can have issues with draining too freely due to the small, light particles in the sandy soil. As such, it can be a good idea to add more organic matter into the soil to act as a sponge and not let the water drain as freely. This works by binding the soil particles together, meaning that they will not wash away as easily, and this can help retain the water and give a firm foundation for the plants to grow. This is always best to be carried out in the spring and autumn, as with other mulching. 

Layering the organic materials on the top is less advisable than mixing it all together, as this will evenly distribute the compost/mulch, and the plant’s roots will be able to find the moisture more easily than if it were to be placed on top. Slow-release fertilisers and less frequent, more deep watering can really aid in improving sandy soils as sandy soils are less rich in nutrients than other types of soils, and the deep watering will ensure that there is less chance of the water all simply draining away, especially with the added organic matter. 

Improving Chalky Soils

Unfortunately, with chalky soils, keeping them fertile for very long is very difficult. If there is any clay present, this will help, but if not, the best route to take is to keep applying compost and fertilisers to improve soil structure. This will also aid in water retention, particularly if more organic matter is added. Be sure to till the soil to ensure that everything is being mixed in – this will also help to break up the soil if there are any larger chunks of chalk in the soil. 

Chalky soils are not as versatile as other soil types in that it is always best to choose a planting scheme that will work with chalk soils, to begin with, rather than relying solely on improving the soil. It is very difficult to change the pH of chalky soils as they will be naturally alkaline due to the limestone/chalk. Therefore, planting acid-loving or ericaceous plants will not work as well as planting those plants which thrive in an alkaline environment. Plants to be wary of are those which will change colour in alkaline soils – unless that colour is what you desire from your plants – such as hydrangeas. 

Improving Loam Soils

Most gardeners and horticulturalists would consider themselves lucky to have natural loam soil in their gardens, as these soil types will generally need the least effort to improve. This is due to their composition, a balanced mix of sand, silt and clay (often 40-40-20.) This means that loam will be free-draining while still moisture retentive, fertile and easy to dig. Depending on the area, some loamy soils will be more clay-heavy or sand-heavy, but these disproportionate amounts can be worked around if needed. 

Adding a mixture of organic matter and a slow-release fertiliser can help to improve loam soil, ensuring that it is all mixed in, and this will give a very good structure for the soil. Most plants tend to thrive in loam soils due to the balanced mix; fertiliser and organic matter will aid in this. Applying wetting agents can help, as can watering more deeply but infrequently. 

Notes:

Regardless of the soil type found naturally in your garden, add organic material and fertiliser/plant feed. This will be more than enough generally to improve the soil to allow plants to thrive in those environments. Structure, drainage and fertility are the key factors in improving your soil type, so the organic matter is the way to go; mixing it through the soil and mulching on the top layer will aid in all of these factors. This will allow you to grow your plants in this healthy soil.

Activity: Following the information above, review your soil and make improvements where needed.

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Updated on March 5, 2024

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