By looking at and feeling your soil with your hands, you should be able to get a sense of the sort of soil that you are looking at. Damp clay soil clumps together and will form a smooth ball when rolled between the palms. Lighter soils will crumble and not form a ball. Loams will form a loose ball that will break apart easily when handled. Sand and chalk are often visible within the soil when closely viewed. Observing your soil type in your polytunnel up close and over time will help you to gain a better understanding of its properties.
Clay Soil: Pros, Cons
Clay soil is the most nutrient rich type of soil. Unfortunately, it is also the most dense, heavy and prone to waterlogging, and freezing in winter.
Improving Clay Soil
Heavy clay soil can be difficult to work with but many wonderful gardens have still been created in areas of heavy clay soil. The key to successful gardening on heavy clay is to be aware of the problems and limitations of that soil type and to work to improve the shortcomings, while enjoying and maximising the benefits. Finding the right plant for the right place is also key to gardening success – a plant at home on a drought-ridden plain, for example, is unlikely to thrive in heavy clay that is prone to waterlogging. The pH of your soil is also something to consider. Beginning with the fundamentals, here are just a few things you should do to gradually improve heavy clay soil over time:
Add Organic Material
Adding organic material should, without a doubt, be the number one priority for most gardeners, especially those with a heavy clay soil. Rather than digging organic material into the soil, you can simply add organic material, in the form of compost and mulches, on top of your soil. Worms and other soil organisms left to their own devices can then work together as a fully functioning ecosystem to incorporate the matter and nutrients into the topsoil below. Heavy clay will become wet and cold in winter and can bake hard and crack in the summer. Increasing the amount of organic material in the soil will allow heavy clay soils to drain more easily and mulches can help to protect the soil surface in summer and prevent it from drying out and cracking.
Clay soils, with their small particles, can be prone to becoming compacted. Organic materials will help lessen this problem but still, heavy clay soils should be treated gently. Try not to step on or compact your clay soil, especially if it is wet and cold. Treating clay soil gently will help it to retain a more aerated structure and retain its excellent fertility.
Protect Over Winter
Winter can be a difficult time for clay soils as they can easily become waterlogged or compacted. To protect clay soils in winter, it is a good idea to sow a cover crop in autumn. Nature abhors bare soil and leaving soil bare can manage fragile top soil and lead to the leaching of valuable nutrients. With heavy clay soil especially, it is a good idea to sow cover crops/ ‘green manures’ that will remain in place over winter and dug in to provide more organic matter when the spring arrives.
Manage Water and Improve Drainage
Managing water effectively is very important in a heavy clay garden. To help reduce waterlogging, it is a good idea to plant thirsty trees, deep rooted plants such as comfrey to open up channels down through the subsoil and more plants in general to use water. Plants with strong roots will also help to break up and aerate heavy clay soil. If waterlogging is a severe problem in a heavy clay garden in winter then as well as devising a more appropriate planting scheme, it may also be a good idea to create raised beds in particularly bad sections, or to consider drainage schemes such as gravel ditches/ simple French drains to move water. Rather than moving water entirely off site, consider storing it in the ground and in ponds for use in dry weather later in the year. Clay’s ability to retain water can be a benefit as well as a down side to this type of soil.
Plants for Clay Soil Type
Good plants for making the most of clay soil include:
- Betula (birch)
- Malus (crab apple)
Sandy Soil: Pros, Cons
Sandy soil can be low in nutrients, and is not good at holding water, though some plants will thrive in the light, airy conditions.
Improving Sandy Soil
Sandy soil or other soil types that do not hold water and nutrients as affectively can be a challenge for gardeners. But a sandy soil is not an obstacle to creating a wonderful garden to please the eye and provide food for a household. Here are some things you can do to improve sandy soil and make sure that it is better able to provide for the plants in your garden:
Add Organic Material
All soils can be greatly improved by the addition of organic material. In the case of sandy soils, organic material will improve the texture of the soil and its ability to retain moisture and, to a certain extent, nutrients. You can incorporate organic material by digging it into your sandy topsoil and also be layering organic matter on the soil surface as a thick mulch. Chopping and dropping as you build your garden will also gradually improve the soil’s fertility and its ability to retain moisture.
For sandy soils, particularly acidic sandy soils, an application of biochar has been proven to be of use in improving the ability of the soil to retain nutrients. Biochar is charcoal made from plant matter and is also a way of holding carbon in the soil. It can endure in the soil for a long, long time and will aid fertility long term, increasing soil biodiversity and increasing the range of crops that can be successfully grown.
Manage Water and Improve Moisture Retention
Lack of water retention is one of the big problems for sandy soil. Good water management involves building water management devices such as mulch-filled swales to retain all the water that falls as rain on the land. Using mulches and ground cover plants can also minimise the amount of water lost through evaporation. Try to avoid leaving big areas of soil bare – nature abhors bare soil.
As will any soil type, success also depends on choosing plants that are suited to the conditions where you live. Make sure that you choose plants that like a sandy soil. You will have success with more drought-tolerant plants and should of course steer clear of any that require lots of water. Which plants will grow well will also depend on the pH of your soil and the degree to which a gardener has already been able to amend it.
Plants for Sandy Soil Type
Good plants for making the most of sandy soil include:
- Alnus cordata
- Salvia officinales
Chalky Soil: Pros, Cons & Improving Chalky Soil
Chalky soil is alkaline and can also be very free draining. Though is ideal for plants that like an alkaline pH, it can be difficult to grow plants that like an acidic environment.
Generally speaking, you can improve the texture, fertility and water retention of chalky soil by adding organic matter, as for sandy soil, above. You can determine exactly how alkaline your soil is with a pH meter. If you wish to grow acid-loving plants, it is best to grow these in containers if you have a very alkaline soil. If your soil is slightly alkaline, you can make soil slightly more acidic by adding a mulch of acidic material like pine needles. You can also use acidic substances like vinegar to make a liquid feed.
Plants for Chalky Soil Type
Good plants for chalky soil include:
- Quercus robar
- Rosmarinus officinalis
Acidic Soil: Pros, Cons & Improving Acidic Soil
Soils that are on the acidic side in the UK also often tend to be fairly high in nutrients and water retentive. While you will struggle to grow plants that need an alkaline pH, acidic soil will be good for growing ericaceous (acid-loving) plants.
The structure of acid soils can often also be improved by the addition of organic matter. If you have determined that your soil is very acidic, you can make it less so with the addition of lime, though this is generally considered to be a fairly drastic measure. Planting appropriate plants for the conditions is usually a better and more effective response, and certainly a more sustainable one.
Plants for Acidic Soil Type
Good plants for acidic soil include:
- Liriope muscari
- Pieris japonica
- Japanese anemones
The above should help you make the most of your soil type, whatever you are faced with in your garden and in your polytunnel. Share your own suggestions regarding how to make the most of your soil type in comments 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.