Distilling Aromatic Waters in the Medicinal Forest Garden: Part 2

by | Jan 28, 2022 | agroforestry, cultivation, forest garden, garden, harvest, herbal medicine, medicinal, permaculture, plants, research, skincare, trees

In this blog about health from volatile compounds given off by trees I focus on key essential oil constituents and examples of trees to distil. In Part 1 I wrote about pinenes and their effects, with some suggestions of trees to harvest. Here in Part 2 there are more medicinal constituents such as caryophyllene and limonene with further species suggestions for distillation. 

Fantastic aromas promoting immunity

While pinenes are characteristic of conifer trees, there are other therapeutic essential oil components commonly found in plants. Beta-caryophyllene is a sesquiterpene found in plants as wide-ranging as black pepper, chaste berry, clove, hemp, hops, lemon balm, lemon eucalyptus, rosemary and prickly ash. With its spicy odour, it is known from research studies for its effects on the endocannabinnoid system – especially for anti-inflammatory effects on the immune system and reduction of pain through binding to cannabinoid 2 receptors (Johnson et al., 2020). This sesquiterpene could be a contributor to the benefits of forest bathing, shown by Li (2009) to significantly increase immune function, an effect lasting up to 30 days. That study showed that a three-day trip to a forest area in Japan led to increases in natural killer cells and other elements of immune function alongside decreased production of stress hormones. 

Creating health-promoting forest areas

The fresh, woody and spicy aromas of pinenes and caryophyllene are just a few examples of key volatile chemicals found in trees which may contribute lasting therapeutic benefits from visiting a forest. Another significant essential oil component is d-limonene, found in citrus and pine trees as well as aspen, frankincense, cedar, chaste berry and juniper, and identified in research studies to have antiproliferative effects on cancer cells alongside other useful anti-inflammatory effects. The strength of response may be variable, just as volatile compounds reported in the forest air can vary a lot. These findings help to underpin initiatives to develop healing gardens and woodlands (Antonelli et al., 2021).

Health benefits and type of forest

Examples of studies based in both broad-leaved and conifer forests have been used to show the mental and physical benefits of forest bathing. Interestingly, however, the number of trees encountered may not be directly proportional to therapeutic benefits. In a review of studies of forests and therapeutic benefits, Kim et al. (2021) showed that the greatest improvements in emotional and cognitive health were associated with thinner stands of trees, specifically where there were less than 500 trees per hectare. The review found that benefits decreased as the density of trees became greater. The explanation for this finding that mental health improvements varied in different forest settings is not yet known, and there are many other variables still to be explored in understanding the effects of forests on health.



More medicinal trees and shrubs to grow and distil

We can bring the aromatic delights of trees (and shrubs) into our own homes through distillaton. As previously mentioned, trees (and shrubs) can be highly productive of leafy material to distil. Distillation of fresh plant material is usual, though sometimes it is more convenient to dry the plant material and use it later. If well-dried then the aromatic constituents can still be gained in later distillation. Once made, the keeping qualities of distilled waters and hydrosols will vary and should be stored in glass bottles in a refrigerator, checking regularly for any sign of deterioration up to 1-2 years. If a distilled water or hydrosol is not rich in essential oils then a way to preserve it for longer is to add add 15% alcohol.

Benefits and disadvantages

The benefits of distilling aromatic waters are multiple as (a) a water extract is produced with therapeutic constituents; (b) this makes a longlasting product if well kept; (c) this is a good way to use up lots of plant material; (d) there is a bonus of essential oil if sufficient plant material used; (e) usually fantastic aromas are created; (f) harvesting can be over a longer period if material is well-dried. There are a few disadvantages which are (a) set-up cost for equipment for distillation may be high; (b) doing the distilling requires time for plant material preparation and supervising the still; (c) you may need lots of good-sized glass storage jars and refrigerator space. Also, bear in  mind that the detailed use of hydrosols is less well understood than essential oils or other preparations, although more and more experience is being gathered. For a detailed overview of commercial uses of essential oils from forests and their application in food, cosmetics and other fields, see Gonçalves and Romano (2021).

Some more aromatic trees and shrubs we have tried (more extended profiles of these can be found in The Medicinal Forest Garden Handbook):

Rosemary (Salvia officinalis)

This is good to distil for both essential oil and hydrosol, and is a great plant to begin with if you are new to distillation. Ideally harvest the leafy stems before flowering begins, prune by cutting back the top third of each stem. Strip the leaves off the stems (the stems can be composted). Steam distillation of rosemary produces a strongly aromatic water that keeps well. Around 2% of essential oil can be expected and the essential oil is high in α-pinene and β-caryophyllene.

Sweet bay (Laurus nobilis)

A hydrosol of the leaves is rich in β-pinene and limonene. Ideal for a sheltered situation where this shrub can grow quite large, the sweet bay offers excellent opportunities to prune or pollard for leafy growth. To distil you can strip the leaves from prunings – or the leaves can be gently dried for later use. The sweet bay has a reputation for use in digestive complaints, and the hydrosol can be used as a mouthwash or gargle

Chasteberry (Vitex agnus castus)

This plant is rich in limonene and β-caryophyllene. It is a shrub that does best in more sheltered situations with plenty of water and free-draining. The chasteberry loves sun and if well pruned will produce profuse leafy stems flowering mid to late in the summer, though it is unlikely to produce berries in the UK. The flowering leafy stems can be used for distillation. The hydrosol is said to be a ‘gentler’ form of the hormonal balancer but we cannot confirm this.


Antonelli, M. , D. Donelli, G. Barbieri, et al. 2020. Forest volatile organic compounds and their effects on human health: A state-of-the-art review.  International Journal of Environmental Research and Public Health17:6506. DOI: 10.3390/ijerph17186506.

Gonçalves, S., and A. Romano. 2021. Aromatic oils from forest and their application. In Non-timber forest products: Food, healthcare and industrial applications, edited by A. Husen et al., 19-37. Springer.

Johnson, S.A., D. Rodriguez, and K. Allred. 2020. A systematic review of essential oils and the endocannabinoid system: A connection worthy of further exploration.  Evidence-Based Complementary and Alternative Medicine 2020:8035301.

Kim, E., S. Park, S. Kim, et al. 2021. Can different forest structures lead to different levels of therapeutic effects? A systematic review and meta-analysis.  Healthcare (Basel) 9(11): 1427.

Li, Q. 2010. Effect of forest bathing trips on human immune function.  Environ Health Prev Med 15 (1): 9-17. DOI: 10.1007/s12199-008-0068-3.

Stobart, A. 2020. The medicinal forest garden handbook: Growing, harvesting and using healing trees and shrubs in a temperate climate. East Meon, Hampshire, UK: Permanent Publications.