Thyme is a sun-loving Mediterranean herb and will do well in a polytunnel, where it will enjoy the warmth and the potential for drier and better drained soil during the colder months. Thyme is a great addition to your polytunnel, not only due to the fact that it is a useful culinary herb but also due to its properties as a companion plant which can aid other crops that you grow.
Thyme will grow well in the same conditions as lavender, and other herbs such as rosemary and marjoram. It will need a position in full sun and will prefer a slightly alkaline soil. Thyme will be suitable for growing either in containers or in a bed in your polytunnel. Drainage is very important so if you have a dense, clay soil you will need to amend it with plenty of grit or sand in order to ensure that water is able to drain away effectively from the roots.
Thyme can be grown from seed though it is easier to grow it from small plants, which should be placed into their growing positions in the spring. Mulching the area around your thyme with some grit or small stones will help to ensure that the drainage is good enough and further help to prevent root rot.
The flavour of thyme is not really compromised by allowing the plant to flower, which is good news as when it is in flower, thyme is attractive, not only to humans but also to a range of beneficial insects which will help you to control a number of different pest problems in your polytunnel. Since it attracts ladybirds and hoverflies, which eat aphids, thyme can be a beneficial companion plant for a range of different crops.
Pinching the tips of the growing stems for use in the kitchen will encourage the plants to bush out and then regular harvesting will help to encourage the continuation of new growth. To use, you will need to strip the small leaves off and discard the woody stem. It is best to stop harvesting around a month before your first frost date in your area, so that the plant does not go into the coldest season with new and tender growth that will be more easily damaged. Thyme can be used fresh, or dried and stored in an airtight container for later use.