Caring for the soil is one of the most important tasks in a sustainable polytunnel. If you want your polytunnel to continue to produce food for years to come, making sure the soil is healthy should be a top priority. In this guide, you can learn about creating healthy soil, and discover how to determine your soil type – something which is vitally important to caring for and improving your garden.
The Importance of Healthy Soil
Without a healthy soil ecosystem, organic gardeners will not be able to produce food from their polytunnels or from other growing areas in their gardens. The soil makes it possible for plants to grow – providing water and nutrients to plant roots. Bacteria, fungi and other organisms work together beneath the surface – the hidden helpers in our growing efforts.
A ‘No Dig’ Gardening Approach For Healthy Soil
A ‘no dig’ gardening approach is the best way to keep soil healthy. In such an approach, the key idea is that the soil ecosystem is left as undisturbed as possible. Rather than digging in or tilling the ground, growing areas are allowed to function with minimal disruption from the gardener.
Leaving Soil As Undisturbed as Possible
In a ‘no dig’ gardening approach, gardeners leave the soil ecosystem to function as it should. By leaving the soil system intact, organic gardeners can make sure that they do no damage to the delicate web of soil biota beneath. This web can then function as it should to transport and deliver water and nutrients to your plants.
Avoiding Bare Soil
Avoiding bare soil is also a key way to protect that soil in an organic polytunnel. Over time, bare areas of soil can lose too much moisture, or become depleted of certain nutrients, which are washed through by watering. For this reason, organic gardeners should attempt to keep growing areas covered – either by plants or by mulch.
Mulching is the main method by which ‘no dig’ gardeners add nutrients to and protect the soil. Rather than digging in organic matter, gardeners adhering to this way of doing things will lay organic matter as a mulch over growing areas and around plants. By choosing the right mulches for the right places, organic gardeners can help to retain moisture, protect the soil, and add the nutrients that are required by the plants grown there.
Nitrogen Fixers/ Dynamic Accumulators
Another important way to ensure that the soil contains the required nutrients, and is replenished in key nutrients over time is by planting species that can help to gather nutrients and return these to the topsoil in growing areas. Nitrogen fixers, such as legumes like peas and beans, have beneficial bacteria in root nodules which take nitrogen from the air and return it to the soil. Other plants, such as deep rooted comfrey, dandelions, yarrow or borage, for example, will gather nutrients from far below the soil surface. When chopped and dropped in place as a mulch, the leaves of these plants will decompose and return these nutrients to the upper layer of soil, where they can be used by your polytunnel crops.
One final way in which organic gardeners can take care of the soil is by means of crop rotation. Rotating annual crops between different growing areas can help prevent the soil from being degraded or denuded of certain nutrients over time. It can also help to stop disease from taking hold in your growing areas.
What Type of Soil Do I Have?
Those growing food in their polytunnels should also know that determining soil type in a polytunnel garden is important. Knowing your soil type will help you decide what best to grow, and help you to improve matters to increase your yield and reduce your risk of encountering a wide range of problems.
While some soil types are more challenging than others, it is possible to grow a range of edible produce year round in all types – you just have to know how to tackle each challenge. In order to know how to cope with your soil type, the first stage is always to determine the characteristics of your soil. Only when you know the characteristics will you be able to amend the soil accordingly to get the best growing area possible where you live.
The Characteristics of Clay Soil:
Particles less than 0.002mm in size.
Good fertility (nutrients are bound to the clay minerals in the soil).
Hold water well.
‘Heavy’ and claggy, easily compacted when wet, bakes hard in summer.
Slow to drain.
Slow to warm up in spring.
The Characteristics of Silty Soil:
Particles of 0.002 – 0.05mm in size.
Fairly high in fertility.
Reasonable water retention.
The Characteristics of Sandy Soil:
Particles of 0.05 – 2mm in size.
Easy to cultivate and work.
Warm up quickly in the spring.
Dries out quickly.
Low in nutrients, which become quickly washed out in rain.
Can be very acidic.
You may also find that you have chalky soil. Chalky soil also contains calcium carbonate or lime. This type of soil’s primary characteristic is that it is alkaline in nature. In addition to the primary composition of the soil where you live, it is also important to determine its pH levels, as this will also determine what can be grown there, and how it can best be amended to grow what you wish to grow.
Peat is another soil type. Peat soils are acidic, moisture retentive and highly fertile, though peat soils are rarely found in gardens in the UK.
How To Test Soil Type
Determining soil type involves working out the composition of your soil, its pH and how fertile it is. The first thing to consider when trying to learn more about the soil in your garden is what is already growing there, and in the surrounding area. Looking at what grows in the vicinity can give you a whole range of clues about what the soil is like. As well as looking at the vegetation around about, here are some more ways to learn more about the soil in your garden:
Determining Soil Composition
Soils in the UK are usually contain one or more of the following particle types: clay, sand, or silt.
In a heavy clay soil, very small particles are found. These particles lump together – they are rich in nutrients and store water well. On the other hand, they can become waterlogged, and can be prone to compaction.
Where sand predominates, the particles are larger. Soils are very free-draining, and are not as good at retaining nutrients or water.
Silt particles are somewhere in between, with some of the characteristics of each of the above.
Many soils have a mixture of the different particle sizes – these soil mixtures are called ‘loams’. You may have a clay loam, a silt loam or a sandy loam. The ideal scenario is a ‘perfect loam’, where the clay and silt or clay and sand particles are in balance, creating a soil that drains well, yet retains water and nutrients.
Observing and digging into your soil should immediately give you a range of clues as to which soil type you have in your polytunnel and elsewhere in your garden.
To get a better idea, take a moist lump of soil and roll it between your palms. A sandy soil will not form into a ball but will crumble apart easily. Where more clay is present, you will be able to roll the damp soil into a ball. If you can make a sausage shape, and curl that sausage into a ring without it breaking, then you have a heavy clay soil. Pure silt soils are rare in gardens, but have a soapy, slippery quality and will not clump together easily. If you see white lumps in your soil, it is a chalky soil.
Determining Soil pH
Soil pH is another thing to determine. Knowing soil pH will tell you which plants will grow well, and how you may wish to amend the soil to grow the things you want to grow. If you are not sure whether you have alkaline soil, take some and place it in vinegar. If it froths up, it is high in lime and alkaline in nature. PH tester kits are also available. Other plants already growing locally will also give you a clue.
Determining Soil Fertility Levels
Finally, you will want to determine how fertile your soil is and how much organic matter it contains. Again, observing the local environment and what grows there will help you determine how much work you’ll have to do to grow food in the soil in your polytunnel. You can also learn a lot about the fertility levels in your garden by observing the plants that you grow. Plants you cultivate can provide clues about which nutrients may be lacking in your growing areas.
Have you determined the soil type in your garden? Have you succeeded in improving the soil in your garden? Feel free to share your comments and suggestions for other gardeners below.
Elizabeth Waddington is a writer and green living consultant living in Scotland. Permaculture and sustainability are at the heart of everything she does, from designing gardens and farms around the world, to inspiring and facilitating positive change for small companies and individuals.
She also works on her own property, where she grows fruit and vegetables, keeps chickens and is working on the eco-renovation of an old stone barn.