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1. Explore Your Needs; Indulge Your Desires

As you peer into the future, imagine how you might interact with your dream garden. Take a moment to write down all the reasons you wish to grow herbs, and how you might incorporate their medicine and beauty into your life. Then, think about how your garden will evolve with time, and which needs are the most important. Will it be a place of refuge, with secret nooks, replete with peaceful statues and comfortable seating nestled under verdant arbors? Do you envision your gardens as an inspirational educational setting, with wide paths and ample signage for visitors? Is your goal to grow herbs for your own apothecary and kitchen or do you have an herbal products business?

In my own garden’s incarnations, I’ve had to adjust my plans, according to how my needs—as an herbalist, photographer, and teacher—have evolved over time. Last year I moved and created new garden beds, which gave me the opportunity to think about my own changing relationship with my plantings. There is needing on a practical level—the necessary volume of plant material for making medicine, a comfortable place to teach students about cultivated medicinals, and a diverse array of herbs to photograph—and then there are the intangible needs. As I envision the layout of the new garden beds I’m creating along the contour of the land, I am mentally weaving a unique tapestry from the fine threads of beauty and green companionship—the perfect view for a spot of tea at sunrise, and a shady nook for rest during the heat of day. My first gardens were born out of the need to provide herbs for my tincture business. As my enterprises shifted, my plantings also became a reservoir of propagating material for my herbal nursery. Additionally, my gardens have served the valuable role of an educational setting—hundreds of herbal students have learned about cultivated medicinal herbs (and the weeds in between, of course) over the years. I like to teach about herbs in the presence of the plants themselves, which means class time often consists of students perched in the pathways between garden beds, clustering around the plant-at-hand.

Juliet Blankespoor in her garden.

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One of the biggest harvests we reap from the garden can’t be dried for tea or prepared into a tincture. This invisible, yet valuable reward is a deeper connection with our medicine. One of the ways we can become more intimate with medicinal herbs is by growing them in our gardens. Seeing an herb every day inspires curiosity, which leads to learning medicinal attributes to traditional preparations. It almost feels like a slow courting, with lots of flirtation before the first kiss of harvest. If you have limited time to devote to your garden, start with a handful of plants, and build your garden as time allows. Another possibility is to interplant a few companion herbs into your vegetable garden, which may not feel like much of a stretch, time-wise, and will offer the added bonus of attracting beneficial insects (see the section on companion herbs below).

If you are a seasoned gardener, you already know that it’s far too easy to plant a bazillion seeds in the springtime, when the future is bright and your garden beds are empty. When all those seeds germinate and you are left with more plants than you will ever need, it is easy to succumb to the temptation of finding them homes in your garden. What’s an extra calendula tucked in here, another sweet little valerian plant over there, you ask yourself? It can quickly add up to a lot of extra work to care for plants that you will never harvest. Come summertime, when the bugs are biting and the sun is blazing overhead, you may be cursing your spring-self, who thought it prudent to plant ALL those seedlings.

So, share the wealth of starts with friends and community gardens, host a plant and seed swap for local gardeners, and when all else fails, the compost pile will welcome those babes with tender arms. Think seriously about your needs, and limit yourself to the plan, especially when it comes to perennials, as your overzealousness can turn into overwork for many years to come. As I dream up my new gardens, I am continually asking myself the essential question: Can I live without this herb in my garden? Too many times, the answer is no. I will now be planting one elecampane plant instead of ten (I hope my impetuousness is tempered with a strong memory of all the overwork it has birthed over the years). All right, maybe two elecampane plants, so they won’t be lonely. 

Anise hyssop, echinacea, and calendula.

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2. Make New Friends but Keep the Old

This oldie but goodie, heralding back to my Girl Scouts days, truly made an impression on me, and serves as a useful filter not just for human relations but also for photosynthetic friendships: “Make new friends but keep the old; one is silver and the other gold.” Those of you well versed in herbal dalliances no doubt have your own herbal darlings—growing these treasured allies is an obvious place to start. Try writing down the names of your besties and then researching if they will grow well in your climate.

Now, you may make fast friends with humans, but how might you introduce yourself to a stranger-herb and make a favorable impression? As we explored earlier, growing unfamiliar herbs is a wonderful way to not only develop an intimate connection with your medicine, but also learn about each herb’s uses, especially if they flourish in your garden and you need to figure out what to do with the bounty! Try welcoming a few unfamiliars into the flock every growing season. It’s a stupendous method for befriending new medicinals and expanding your repertoire as an herbalist.

Anise hyssop, mugwort, and eucalyptus.

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If you’re a newbie, consider reading my article on the Top Ten Medicinal Herbs for the Garden for inspiration. I chose these plants based on ease of cultivation, along with medicinal usefulness and versatility. In an ideal world, we would each have our personal list of top ten garden herbs tailored to our particular climate and health concerns. But the list can serve as a jumping board of sorts, in creating your own unique dream medicinal herb garden.
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3. Lavender is not Kale

While this statement is no shocker, it simply sums up why folks often have trouble growing herbs from seed, while, in contrast, sprouting their favorite veggies, such as kale or tomatoes, is easy peasy. Vegetables have been bred for countless generations, through millennia of cultivation, for uniform, quick and relatively easy germination. Medicinal and culinary herbs are a different story. Many of the herbs we grow are perennials, which typically have a more selective strategy for germination (with less of the live-fast, die-young strategy of annual plants). They need coaxing, cajoling and an ear pointed toward their needs. If you want to grow herbs from seed, you’ll need to give them some extra attention in the form of stratification, scarification and surface sowing.

Passionflower seeds germinating.

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These techniques aren’t too hard to master after a few rounds, and an extra bonus for learning these crafty propagation maneuvers is that you’ll be able to successfully germinate the seeds of most trees, shrubs, and perennial wildflowers and natives. After many years of owning a medicinal herb nursery and birthing thousands of herblings, I put together this resource: Guideline to Growing Medicinal Herbs from Seed.

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4. Grow with Cultivated Wild Abandon

I am entranced by the graceful exuberance of cottage gardens—informal plantings with varying heights and textures, created from a palette of diverse flora. Such gardens are reminiscent of a meadow at the forest’s edge, colored with interspersed wildflowers, and mirror what actually happens in nature. When I view formal plantings filled with repetitive monotonous monocultures, I find them stifling and over-controlled, but it’s more than an issue of style. When plants are grouped with only their kind, they are easy targets for pathogens and problem insects. Conversely, when plants are interspersed with other species, it makes it more challenging for diseases and insects to spread. Additionally, plants make compounds that deter predation, many of which are aromatic molecules—these serve to protect not only the emitter, but also the neighborhood at large.

Polycultures

Most traditional methods of agriculture involve interplanted food crops with useful edible and medicinal weeds filling the gaps in between. When the first Europeans encountered the effusive gardens of Native Americans, they dismissed the gardens as “untidy” and proclaimed the gardeners lazy, failing to see the wisdom in their new neighbors’ agricultural practices. Most of you are likely familiar with the Native plantings of the three sisters: corn, beans and squash. The beans help the “family” by fixing nitrogen and feeding the hungry corn, and in return, the corn gives the beans a surface to climb up. The squash grows in between, acting as a living mulch, holding in the moisture and providing habitat to beneficial animals (which prey on the insects that eat the plants). Where germination is incomplete, the disturbed ground allows for weed seeds to germinate. The edible weeds are allowed to grow, and are actually loosely tended, as they are an important part of the gardens productivity. In the southwestern United States, there is a “fourth sister”—the Rocky Mountain bee plant (Cleome serrulata), which is a weedy native wildflower with edible shoots. Its flowers also attract pollinators, which serves to increase bean and squash production by increasing pollination and fruit set. The three sisters method of planting is the most well known example of a polyculture—a fancy word for manygrowing, or growing a diverse array of many crops together. Think the opposite of monoculture.

Herbal polyculture with passionflower on the trellis, purple shiso, roselle hibiscus, spilanthes, astragalus, and rose.

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An example of an herbal polyculture that has worked well in my garden is passionflower, comfrey, gotu kola, and jiaogulan. The passionflower climbs up a trellis made out of a bamboo tripod, which creates a leafy teepee of shade and moisture. Gotu kola and jiaogulan prefer, in my climate, part sun and a little extra moisture, which the towering passionflower vine provides quite nicely. Both gotu kola and jiaogulan spread, thus acting as a living mulch—holding in moisture and suppressing weeds. Passionflower attracts bees and other pollinators into the garden, helping to increase fruit set of nearby vegetables. This is just one example of an herbal polyculture; with a little observation and imagination you can design your own mini botanical communities.

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5. Call on your Garden Superstars

These garden superstars have special characteristics, making them especially desirable in polycultures. Their superpowers include, but are in no means limited to: attracting beneficial insects that prey on pest-insects; accumulating nutrients from deep in the soil, thus making the nutrients available to neighboring plants; fixing nitrogen, and thus “fertilizing” surrounding plants; sheltering other plants from the sun and/or wind; and attracting pollinators, which is helpful in beekeeping and increasing fruit and vegetable production. Many medicinal herbs are superb companion plants, and some even possess multiple companionable traits. I will list some of my favorites here, in their respective categories.

Dynamic accumulators mine nutrients (such as N, K, P, Ca) from deep in the soil, concentrating them in their leaves, and then releasing the nutrients when they die or shed leaves. They often have deep taproots and act to break up soil, in addition to enriching it. Some accumulators are initial colonizers of disturbed soil, and are especially adept at optimizing their own nutrition in poor soils, even without deep roots. Examples of the best herbal dynamic accumulators include: comfrey, yarrow, black birch, yellow dock, dandelion, linden, nettles, chickweed, licorice, German chamomile, watercress, and chives.

August 2021 Safety Update: Comfrey contains pyrrolizidine alkaloids (PAs), which can be harmful to the liver over time when ingested internally. Recent research shows that the PAs found in comfrey (and other PA-containing plants) can be taken up by other plants when grown in close proximity or when comfrey is used in the garden as mulch or fertilizer. In light of this, we are recommending that comfrey should not be interplanted with herbs or food plants in the garden that will be ingested or used as mulch or fertilizer to err on the side of caution. However, mature compost that includes comfrey does not seem to contain PAs once it has been fully composted according to this study.

Nitrogen fixing herbs are able to convert atmospheric nitrogen into a bioavailable form of nitrogen, which they release into the soil when they die or lose leaves. Perennial woody nitrogen fixers will also release nitrogen from the roots when they are pruned or cut back. Examples of herbal nitrogen fixers include: bayberry, red clover, alfalfa, sweetfern, redroot, licorice, fenugreek, sweet clover, wild indigo, astragalus and many species of alder.

A basket full of harvested red clover.

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Nectary plants are especially attractive to beneficial insects, often producing copious amounts of nectar and/or pollen. Depending on the species of plant, they can lure honeybees, native bees, predator insects, butterflies and hummingbirds into the garden. Herbal nectary examples include: anise hyssop, milkweed, yarrow, comfrey, alder, birch, wild indigo, hawthorn, wintergreen, bee balm, calendula, elecampagne, lovage, angelica, echinacea, mullein, and wild bergamot.

Monarda fistulosa.

6. Think Inside the Box

Not everyone has a field or lawn they are able to transform into their dream herb garden. If you only have a patio, or live in an urban area and have limited outdoor space, here are some tips to maximize your plantings. A time-tested solution for growing in a limited space is container gardening—planting in the “box.” Larger ceramic pots, retired bathtubs, and wooden barrels can hold a surprising number of herbs, especially if trailing herbs are planted at the perimeter and taller plants at the rear. Plan for varying heights, and more plants can grow companionably. Please see my article on Growing Medicinal Herbs in Containers.

Calamus and skullcap growing in a retired bathtub.

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Go Vertical

Train vining herbs up onto a trellis, arbor, or pergola, to maximize your use of space. Passionflower, hops, raspberry, jiaogulan, and climbing roses are a few possibilities. Hops can grow to gigantic proportions, so you will probably need to tame it by cutting it back, or give it a large fence or wall of a building. Many of the above herbs will spread by runners, and quickly take over a garden. Planting in containers can help to limit their spreading. Another option is weeding out the runners a few times a year.

Maximize Yields

 Certain herbs can be harvested multiple times throughout the year, in a “cut-and-come-again” style (similar to micro greens cultivation). Give the plants a “haircut” early enough in the season, and they grow right back. I harvest the following herbs in this fashion, two to three times during the growing season: gotu kola, holy basil, spilanthes, thyme, California poppy, passionflower, basil, rosemary, chickweed, violet, lemongrass, sage, bee balm, meadowsweet, anise hyssop and lemon balm. Growing these herbs can effectively double or triple your yield for every square foot of precious dirt.
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7. Become a Niche Ninja

One of the many nifty aspects to growing medicinals is that we can truly diversify the plants we grow by capitalizing on varied habitats. Additionally, we can wisely choose herbs that will thrive in our climate instead of catering to herbs who just really don’t want to be in our garden, no matter how kind we are to them. There’s a whole bevy of medicinals that thrive in the shade, many of which are endangered from overharvesting or habitat loss. Goldenseal, ginseng, partridgeberry, bloodroot, wild yam, blue cohosh and black cohosh are a few to consider if you have a shady habitat under mixed hardwoods. To learn more, check out my article Cultivating Medicinal Herbs with a Focus on Cultivating Woodland Medicinals.

Goldenseal (Hyrdrastis canadensis).

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If you have a wet spot, consider these moist-loving medicinals: blue vervain, calamus, elderberry, meadowsweet, stinging nettles, skullcap and marshmallow. Even if you don’t have such a habitat, you can simulate it by planting in slowly draining containers. Learn more about this sneaky trick here.

Wetland medicinals (marshmallow, blue vervain).

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For those of you who live in a sultry climate, here’s a smattering of herbs to explore: ashwagandha, holy basil, lemongrass, hibiscus, gotu kola, spilanthes, and calendula. Arid climates also have their own cache of medicinals to choose from, including lavender, rosemary, thyme, ephedra, desert willow, olive, and white sage.

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8. Think Like a Meandering Stream

The following information is perhaps the least glamorous aspect of garden planning, however, you’ll be quite pleased if both humans and materials are able to move throughout the garden with the ease and dexterity of a gently tumbling mountain stream.

Pathways

Proper placement of pathways and designing for materials distribution are admittedly not the most exciting aspect of creating a garden, but they are nonetheless essential. There are many types of pathways: mowed greenery, mulch, gravel, stones, recycled concrete “stones,” and bricks. Each option has its pros and cons. Many growers plant a low-growing, nitrogen-generating cover crop, such as white clover, to serve as a green pathway. It can be periodically mowed and the clippings used as a “green manure,” and applied as mulch or added to compost. Just remember that clover attracts bees, who are certainly wonderful to entice into any garden, but can present a challenge for the barefoot gardener. In smaller, more formal gardens, plantings of low-growing herbs such as thyme and chamomile make for aromatic paths or small “lawns”. Wood mulch makes for a pleasing pathway; it has to be reapplied every year, but has little maintenance other than that. An added benefit of wood mulch is that it can be inoculated with edible and medicinal mushrooms. Utility companies or city dumps often give away fresh wood clippings from sawed-off trees and limbs. Bark mulch is finer than wood clippings, so it degrades more quickly and needs to be reapplied more often. In addition, it costs money, and is a byproduct of the lumber and pulp industries.

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Gravel or rock pathways require less maintenance than the aforementioned choices, especially if they are built right and the path is lined with a border (rocks, lumber, inverted repurposed wine bottles, etc.). Keep gravel pathways separate from mowed area—when rocks find their way into lawns they can pose a serious hazard. If your path is on a slope, finer and smoother rocks can create a hazardous slippery-slidey surface. Gravel and ornamental rock delivery can be surprisingly pricey, but the paths will last for many years, especially if you install a weed barrier under the rocks. An interesting and sustainable option is “urbanite” – large chunks of re-purposed, used concrete. Smaller pieces of urbanite can be used to create borders around beds and paths, and larger chunks in retaining walls. Flatter segments of urbanite can be used in lieu of flagstone pavers, and placed in coarse sand or gravel. Primary paths should be a minimum of three feet wide to accommodate a cart or wheelbarrow. For secondary footpaths, eighteen inches should suffice. If your garden will be used for educational purposes or entertainment, wider paths are in order.

Jim Duke’s Green Farmacy Gardens.

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Garden and Materials Access

Planning a central location for vehicles to bring amendments, such as mulch, compost, manure and soil, can make for an easier flow throughout the garden. There should be ample room for a work vehicle to safely turn around or back up, as well as space for piles of amendments and materials. If your garden is terraced or sloped, it is beneficial to design for a materials area higher up, so you can travel downhill to distribute materials, rather than up.

Angel trumpet growing in Cornell Plantations Herb Garden (angel trumpet is poisonous).

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9. No Need to Reinvent the Wheelbarrow

I learned about growing medicinals through trial and error and by scouring any herb cultivation book I could get my hands on. The personal experience was invaluable, but in today’s info-laden world, it’s so much easier to get started! There are innumerable online and printed resources for learning more about growing medicinal herbs. Here are some of the ongoing resources we offer, and a list of the treasured resources we turn to every growing season.

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Juliet’s Favorite Herb Gardening Books

Growing At-Risk Medicinal Herbs: Cultivation, Conservation and Ecology – Richo Cech. Detailed instruction on the cultivation requirements for at-risk plants including ginseng, goldenseal, the cohoshes, bloodroot, etc.

Herbal Emissaries: Bringing Chinese Herbs to the West – Foster and Chongxi.

Excellent all–around reference for popular Chinese herbs. Includes information on medicinal use, processing and cultivation for each herb.

Herbal Renaissance – Steven Foster. Similar to the above description except this book covers Western Herbs. These two books are on my top shelf of references; the detail and experience Foster shares so gracefully make these indispensable sources for any herb gardener.

The Illustrated Herb Encyclopedia; A Complete Culinary, Cosmetic, Medicinal, and Ornamental Guide to Herbs – Kathi Keville. One of my long-time favorite herb references. Provides more cultivation information than most general herbals. Beautiful illustrations. Recipes, historical reference, aromatherapy etc.

The Medicinal Herb Grower – a Guide for Cultivating Plants that Heal, Volume 1 – Richo Cech . A good beginning book to cultivating plants in general, but focusing on medicinal herbs. Vegetative propagation is explored: cuttings, divisions, layering as well as germination specifics: stratification, scarification, light-dependent and heat-dependent germinators. Composting, soil, mulching, seed-saving and harvesting are also covered.

Growing and Propagating Wildflowers of the United States and Canada – William Cullina. One of the finest native plant growers’ manuals. Excellent photos, cultivation, and propagation information for many of our natives.

Growing and Marketing Ginseng, Goldenseal and other Woodland Medicinals – W. Scott Persons and Jeanine M. Davis. The most thorough and technical guide geared towards the commercial grower of forest medicinal herbs.

The Herb Society of America New Encyclopedia of Herbs and their Uses – DK , Revised edition 2001 – Deni Brown. Excellent reference for the cultivation and usage for more than 1,000 medicinal herbs. Each monograph includes cultivation, propagation, harvest, parts used and properties and usage. I use this book for researching cultivars and international plants.

• Looking for seeds or herb plants? Our Link Page has a list of herbal nurseries and seed sellers.

• We curate a dazzling Pinterest Board, filled with our favorite articles on herb gardening, permaculture, and garden design. We only share resources we personally trust, so each pin has our stamp of approval!

• Two Facebook pages with lots of good information on growing herbs: Strictly Medicinals (formerly Horizon Herbs) and our own page Cultivating Medicinal Herbs.

• If you enjoy my botanical bling and writing, visit my Instagram account, where I share daily snippets of herb cultivation, medicine making, botany and ecology.

• Medicinal Herbs and Non-Timber Forest Products – Useful links to many websites and articles devoted to the topic of cultivating medicinal herbs. Dr. Jeanine Davis of NC.

• Fedco Seeds – Cultural information and planting chart for herbs – Fedco chart

• The most extensive DIY online herbal course out there, which includes foraging, botany, cultivation, medicine making and therapeutics— our Online Herbal Immersion Program.

May your gardens flourish, and provide abundance, beauty and healing in your lives!

~ Juliet Blankespoor

Herbal Index

(Includes common name, scientific name, and plant family)

Alder, Alnus spp., Betulaceae

Alfalfa, Medicago sativa, Fabaceae

Angelica, Angelica archangelica, and other species, Apiaceae

Anise Hyssop, Agastache foeniculum, Lamiaceae

Ashwagandha, Withania somnifera, Solanaceae

Astragalus, Astragalus propinquus = A. membranaceous, Fabaceae

Basil, Ocimum basilicum, Lamiaceae

Bayberry, Myrica cerifera, Myricaceae

Bee Balm, Monarda didyma, Lamiaceae

Black Birch, Betula lenta, Betulaceae

Black Cohosh, Actaea racemosa, Ranunculaceae

Bloodroot, Sanguinaria canadensis, Papaveraceae

Blue Cohosh, Caulophyllum thalictroides, Berberidaceae

Blue Vervain, Verbena hastata, Verbenaceae

Boneset, Eupatorium perfoliatum, Asteraceae*

Calamus, Acorus calamus, Acoraceae

Calendula, Calendula officinalis, Asteraceae

California Poppy, Eschscholzia californica, Papaveraceae

Chamomile, Matricaria chamomilla, M. recutita, Asteraceae

Chickweed, Stellaria media, Caryophyllaceae

Chives, Allium schoenoprasum, Amaryllidaceae

Comfrey, Symphytum officinale, Boraginaceae*

Dandelion, Taraxacum officinale, Asteraceae

Desert Willow, Chilopsis linearis, Bignoniaceae

Echinacea, Echinacea purpurea, and other species, Asteraceae

Elderberry, Sambucus nigra, S. canadensis, Adoxaceae

Elecampane, Inula helenium, Asteraceae

Ephedra, Ephedra sinica, Ephedraceae

Fenugreek, Trigonella foenum-graecum, Fabaceae

Ginseng, Panax spp., Araliaceae

Goldenseal, Hydrastis canadensis, Ranunculaceae

Gotu Kola, Centella asiatica, Apiaceae

Hawthorn, Crataegus spp., Rosaceae

Hibiscus, Hibiscus sabdariffa, Malvaceae

Holy Basil, Ocimum tenuiflorum, Lamiaceae

Hops, Humulus lupulus, Cannabaceae

Jiaogulan, Gynostemma pentaphyllum, Cucurbitaceae

Lavender, Lavandula spp., Lamiaceae

Lemon Balm, Melissa officinalis, Lamiaceae

Lemongrass, Cymbopogon citratus, Poaceae

Licorice, Glycyrrhiza glabra, Fabaceae

Linden (or Basswood), Tilia spp., Malvaceae

Lovage, Levisticum officinale, Apiaceae

Marshmallow, Althaea officinalis, Malvaceae

Meadowsweet, Filipendula ulmaria, Rosaceae

Milkweed, Asclepias syriaca, Apocynaceae

Mullein, Verbascum spp., Scrophulariaceae

Olive, Olea europaea, Oleaceae

Partridgeberry, Mitchella repens, Rubiaceae.

Passionflower, Passiflora incarnata, Passifloraceae

Raspberry, Rubus idaeus, Rosaceae

Red Clover, Trifolium pratense, Fabaceae

Redroot, Ceanothus americanus, Rhamnaceae

Rose, Rosa spp., Rosaceae

Rosemary, Salvia rosmarinus, Lamiaceae

Rocky Mountain Bee Plant, Cleome serrulata, Capparaceae

Sage, Salvia officinalis, Lamiaceae

Skullcap, Scutellaria lateriflora, Lamiaceae

Spilanthes, Acmella oleracea, Asteraceae

Stinging Nettles, Urtica dioica, Urticaceae

Sweet Clover, Melilotus officinalis, Fabaceae

Sweetfern, Comptonia peregrina, Myricaceae

Thyme, Thymus vulgaris, Lamiaceae

Violet, Viola spp., Violaceae

Watercress, Nasturtium officinale, Brassicaceae

White Clover, Trifolium repens, Fabaceae

Wild Bergamot, Monarda fistulosa, Lamiaceae

Wild Indigo, Baptisia tinctoria, Fabaceae

White Sage, Salvia apiana, Lamiaceae

Wild Yam, Dioscorea villosa, Dioscoreaceae

Wintergreen, Gaultheria procumbens, Ericaceae

Yarrow, Achillea millefolium, Asteraceae

Yellow Dock, Rumex crispus, R. obtusifolius, Polygonaceae

*August 2021 Safety Update: Boneset and comfrey contain pyrrolizidine alkaloids (PAs), which can be harmful to the liver over time when ingested internally. Recent research shows that the PAs found in these plants (and other PA-containing plants) can be taken up by other plants when grown in close proximity or when comfrey is used in the garden as mulch or fertilizer. In light of this, we are recommending that comfrey should not be interplanted with herbs or food plants in the garden that will be ingested or used as mulch or fertilizer to err on the side of caution. However, mature compost that includes comfrey does not seem to contain PAs once it has been fully composted according to this study.