If you have very alkaline soil, you may find it a challenge to grow edible produce directly in the soil in your polytunnel. However, a mildly alkaline soil need not be a huge disadvantage. There are still a range of edible plants that you can grow even if your soil pH is above neutral.
Generally speaking, unless your soil is extremely alkaline, it is best to work with what you have. Rather than amending the soil pH, which can be a rather drastic measure, it is usually best to simply accept the limitations and grow plants suited to where you live. Here are some of the edible plants best suiting to growing in a polytunnel in alkaline conditions:
Asparagus for Alkaline Soil
Asparagus is ideal for growing in many alkaline soil environments. It thrives in locations with a soil pH of between 6 and 8. Asparagus is one perennial crop that could be well suited to polytunnel growing. Asparagus needs a sheltered and sunny spot where it is protected from strong wind – a polytunnel is perfect for providing that protection and can also help avoid problems with over-watering that can come from unpredictable UK weather.
Most cabbages can benefit from a somewhat alkaline soil, as an alkaline soil can reduce the incidence of certain problems in the brassica family, such as club root. One of the great things about growing cabbages in a polytunnel is that they can be more easily protected from pests such as the cabbage white butterfly.
Broccoli/ Cauliflower/ Brussels Sprouts
Other members of the brassica family also tolerate alkaline conditions relatively well. They can cope with a soil pH of as high as around 7.5. There are a huge array of different members of the brassica family that you could consider growing directly into alkaline soil in a polytunnel throughout the year.
One other member of the brassica family worth singling out for special mention is kale. Kale is particularly useful as a hardy winter crop, especially when grown in a polytunnel. Like other brassicas, kale can also grow at a pH of up to 7.5.
Leeks – An Allium for Alkaline Soil
Leeks are the most tolerant allium when it comes to alkaline soil. While onions can do well is soil with a pH of 7, leeks can do well in soil with a pH of up to 8, making them a great choice for many conditions with alkaline soil.
Peas – A Legume for Alkaline Soil
Peas are a polytunnel staple and can tolerate a reasonably broad pH range. They can survive well in soil with a pH of 6- 7.5. You could consider growing peas for pea shoots and mange tout as well as traditional podded garden peas.
Pole beans are another useful legume, which can tolerate a pH of up to 7.5 and which will help to maintain the fertility of your garden by aiding in nitrogen fixation. Planting pole beans can help keep your garden beds in top condition as well as providing you with an edible yield.
Marjoram thrives at soil with a pH of between 6 and 8. It is one of the Mediterranean herbs that are ideal for polytunnel growing. The polytunnel will help make sure the plants do not get too much water. Marjoram will provide for culinary uses but can also be a useful companion plant for other crops.
Another useful Mediterranean herb for a polytunnel garden is rosemary. Rosemary is also a versatile culinary herb and good for attracting beneficial wildlife. Rosemary has a preferred pH range of 6-7.5 but will tolerate even more alkaline soils.
Thyme grows well alongside marjoram, rosemary and other such herbs. It will do best in soil that has a pH of between 6.5 and 7, but can cope with and grow in soils with a pH of between 7 and 8.5 too. This is also another useful companion plant for vegetable crops.
If you have alkaline soil, then the plants mentioned above could be the best bets for a successful polytunnel garden. Let us know in the comments below if you have any other edible plant suggestions to help others garden in alkaline soil.
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.