Herbs can be extremely useful, not only for adding flavour in the kitchen but also in a polytunnel. As companion plants, a number of herbs are said to promote healthy growth in other plants and many herbs will repel a range of pests. Here are some of the herbs that could be particularly beneficial when grown in a polytunnel:
Rosemary is easy to grow in a polytunnel and is perfect for growing near brassicas and beans. Rosemary's scent has been shown to deter cabbage flies and also repels a range of bean parasites. It will grow well in a container in a polytunnel as it will like the added warmth. It can cope with arid conditions and so will not require much watering.
Thyme (which grows well with rosemary) is also beneficial for cabbages and other members of that family as it repels or distracts cabbage worms, cabbage loopers and cabbage weevils. In addition, thyme is particularly beneficial for a range of crops as it attracts hoverflies and other predatory insects which can help keep the numbers of aphids down.
As an allium, chives are a good companion plant for many different crops. With their strong scent they will, like other members of the onion family, disguise the scent of other crops, such as carrots for example, making it harder for their pests (such as carrot fly) to find them.
Oregano, like a number of other herbs, will attract ladybirds, hoverflies etc. which will help to keep down insect pest populations. Oregano can also be beneficial as a companion crop to peppers, as it will provide ground cover when allowed to grow beneath them. This will help to retain soil moisture and contribute to the humidity required for pepper plants to thrive.
Basil goes very well with tomatoes in the kitchen and what is true there is also true in the polytunnel. When grown under and amongst tomatoes, basil will help the tomatoes and some say it even makes them taste better. Basil can also help asparagus by repelling or distracting some of its common pests.
Many different herbs can be of benefit in your polytunnel. Consider inter-planting a number of different herbs with your other crops as well as placing some herbs in containers near the doors of your polytunnel, which can be moved around as required to suit the crop rotation you have developed.