Yields and biological value of three herbal species from the Lamiaceae family

Lemon balm, garden sage and common thyme are herbal species possessing versatile medicinal properties. They are also used as spices for culinary purposes. In the Polish climate, despite being perennial, these herbs usually grow on plantations for a year. The reason is their tendency to develop more lignified lower parts of stems, which in consequence depreciates the quality of yield and make the plants more sensitive to spring frost when there is no snow cover. The study aimed at evaluating the yielding of three herbal species (lemon balm, garden sage and common thyme) grown from seedlings in south-eastern Poland. Another objective was to determine the content of essential oils and minerals in raw material against the backdrop of the weather conditions during the growing season. The plant height was determined before harvest. Herbs were cut at the beginning of flowering, i.e. mid-July (lemon balm) and mid-August (common thyme); garden sage does not flower in the first year, hence the herb was cut at the end of August. Weight of fresh herbage was determined after the harvest, while air-dried herbage weight, ground herbage weight (for common thyme) and air-dried leaf weight (for lemon balm and garden sage) were assessed after drying under natural conditions. The content of essential oils was evaluated in dried material according to the applicable method descibed in Pharmacopoeia. Quantities of total nitrogen, ammonia, nitrates, phosphorus, potassium, calcium, magnesium, and sulfur were also determined in the harvested material. The height of lemon balm, garden sage and common thyme plants depended on the rainfall sum. Herbs grew higher in the years characterized by larger sums of atmospheric precipitations from May till July. Rainfalls also significantly affected the yields of fresh lemon balm, garden sage and common thyme herbs. In 2006, a year with less atmospheric precipitation, considerably more total nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur accumulated in lemon balm leaves. More total nitrogen in garden sage and common thyme, ammonia in garden sage leaves as well as calcium in common thyme herb were found as well.