In a polytunnel, it is important to take care of the soil. Taking care of the soil will help to ensure that yield remains high and you can make the most of the space you have. One of the fantastic things about a polytunnel is that it can significantly increase the length of the growing season in our climate – but that longer season can mean that soil is depleted if you are not careful to care for it and replenish nutrients when necessary. There are plenty of ways to care for and replenish soil in your polytunnel.
One of the ways in which gardeners can care for their soil over the winter is by planting a cover crop, which will help to stabilise soil and retain nutrients over the coldest months. A cover crop is simply a dense, ground-cover type plant that is sown wherever gaps pop up in polytunnel crop rotation. Choosing the right cover crop can help to maintain the balance in your soil throughout the year and help to prepare it for the following spring's planting. The cover crop can serve many purposes, but basically, the main goal is to cover and protect the soil ecosystem until the early spring, when the cover crop will be chopped and dropped as a 'green manure' to add nutrients back to the system.
Green manures such as vetch, field peas or beans will add nitrogen to a depleted system. Other cover crops, such as mustard can help to manage soil borne pathogens. Mustard has high levels of glucosinolates and can help in a process known as 'biofumigation'. It also grows quickly and will help to keep down weeds throughout winter and early spring. Mustards are not the only brassicas that can be used as cover crops – some useful brassica cover crops can also be picked at for edible leaves over the winter months, serving two or more purposes at the same time.
Cover crops should be fitted into the same rotation plan as other crops in your polytunnel and should be planned carefully to ensure a balance throughout the soil system. It is important to understand the benefits of each individual cover crop and to correctly identify where and when they may be of use in your polytunnel system. Choosing the right cover crops can be part of successfully growing organic produce – produce that will continue to provide a bountiful yield for years to come.