The Slow Infusion Method: Why We Don't Rush Our Oils
There is a jar sitting on my windowsill right now that has been there for three weeks.
It is filled with dried calendula flowers and sunflower oil. Every morning I pick it up, give it a gentle shake, and set it back down in the patch of light that falls across the sill in the late morning. Then I go about my day. The jar sits. The light moves across it. The oil slowly, imperceptibly, turns gold.
In three more weeks, I will strain it. The flowers will go to the compost. The oil — now a deep, warm amber, carrying everything the calendula had to give — will go into salves, balms, and lip care products that will eventually make their way to you.
This is the slow infusion method. It is not the fastest way to make herbal-infused oil. It is, in my experience and in the experience of the traditional herbalists whose work I've studied, the best one.
Let me tell you why.
What Is an Herbal-Infused Oil?
Before we talk about method, let's talk about what we're making and why it matters.
An herbal-infused oil is exactly what it sounds like: a carrier oil in which dried plant material has been steeped long enough for the plant's active constituents — its resins, its fat-soluble compounds, its volatile components — to transfer into the oil.
The resulting oil is not the same as the carrier oil you started with. It carries the plant. Not a synthetic approximation of the plant, not an isolated extract of one compound from the plant, but the whole plant — its complexity, its chemistry, its character — now suspended in a form that can be applied to skin, absorbed, and put to work.
This is the foundation of almost everything in the Rainroot Apothecary line. Not purchased extracts. Not standardized isolates. Oils that we make ourselves, from plants we grow or harvest ourselves, using a process that takes weeks rather than hours.
That choice — to make rather than buy, to wait rather than rush — is not incidental to what we do. It is central to it.
The Two Methods: A Honest Comparison
There are two primary methods for making herbal-infused oils, and I want to be honest about both of them — including the legitimate case for the faster one.
The Heat Infusion Method
Heat infusion uses gentle, sustained warmth to accelerate the extraction process. The most common approaches are:
- Double boiler — plant material and oil in a heat-safe bowl set over simmering water, maintained at a low temperature (ideally below 150°F) for 4–8 hours
- Slow cooker — plant material and oil in a slow cooker on the lowest setting for 8–24 hours
- Oven method — plant material and oil in a covered oven-safe dish at the lowest oven temperature for several hours
Heat infusion works. It produces a genuinely infused oil in a fraction of the time. For someone making a small batch for personal use, or working with a plant whose constituents extract well under heat, it is a perfectly reasonable approach.
The tradeoff is this: heat degrades some of the volatile compounds that make certain botanicals valuable. The same warmth that accelerates extraction also accelerates oxidation, and can alter or destroy some of the more delicate constituents in heat-sensitive plants. You get a faster result — but not always the same result.
The Slow (Cold) Infusion Method
The slow infusion method — sometimes called the folk method, the cold infusion method, or simply the traditional method — uses time rather than heat.
Dried plant material is placed in a clean jar, covered completely with carrier oil, sealed, and left to infuse at room temperature for four to six weeks. The jar is kept in a warm spot — a sunny windowsill is traditional, and genuinely effective — and shaken or stirred daily to keep the plant material moving through the oil and prevent settling.
Over those weeks, the plant's fat-soluble constituents migrate slowly and completely into the oil. No heat means no degradation of volatile compounds. No shortcuts means no compromises in the complexity of what's extracted.
The result is an oil that is richer, more complex, and — in my experience — more effective than what the same plant produces under heat. It also smells different: deeper, more nuanced, more fully itself.
The tradeoff is obvious: it takes six weeks. You have to plan ahead. You have to be patient. You have to remember to shake the jar every morning.
I find that I don't mind any of those things - and in fact, the quiet ritual of it reminds me to slow down and be present.
Why We Choose Slow Infusion — Every Time
There are practical reasons and philosophical ones, and I think both matter.
The practical case:
Certain compounds in the plants I work with most — calendula's triterpenoids and flavonoids, comfrey's allantoin, plantain's aucubin — are sensitive to heat in ways that affect their stability and their activity. Slow infusion at room temperature preserves these compounds more completely than heat infusion does.
There is also the question of oxidation. Every time you heat an oil, you accelerate its oxidation — the process by which oils go rancid. A slow-infused oil, made at room temperature, has a longer effective shelf life than a heat-infused oil made from the same ingredients. For a small-batch apothecary making products that need to remain stable for 12 months, this matters.
The philosophical case:
I learned to make infused oils from my grandmother, who learned from someone before her. The slow method is the traditional method — the one that has been used by herbalists for centuries, long before anyone understood the chemistry of why it worked. It worked then. It works now. The fact that we can now explain why it works doesn't make the traditional knowledge less valid — it makes it more interesting.
There is also something I find genuinely important about the pace of slow infusion. It builds a relationship with the plant. You handle the jar every day. You watch the oil change color. You notice when the plant material has given everything it has to give and the oil has reached its full depth. You cannot rush this process, and in not rushing it, you pay attention in a way that faster methods don't require.
Attention, I believe, is an ingredient. Not in any mystical sense — but in the very practical sense that makers who pay close attention to their materials make better products than those who don't.
Our Process, Step by Step
For those who want to understand exactly what happens between the farm and the finished product — or who want to try this at home — here is our process in full:
Step 1: Harvest We harvest botanicals at peak potency — calendula flowers when fully open, comfrey leaves before flowering, plantain in early summer when the leaves are young and vital. Timing matters. A plant harvested at the wrong moment gives less than one harvested at the right one.
Step 2: Dry Fresh plant material contains water, and water in an oil infusion will cause mold. Everything we infuse is dried first — on screens in a warm, well-ventilated space, out of direct sunlight, until the moisture content is low enough that the plant material crumbles rather than bends. For most botanicals, this takes 1–2 weeks depending on the plant and the weather.
Step 3: Fill the jar Dried plant material goes into a clean, dry glass jar — filled loosely to about two-thirds full. We use wide-mouth mason jars for most infusions. The jar must be completely dry — a single drop of water can introduce mold into the infusion.
Step 4: Cover with oil Carrier oil goes in until the plant material is completely submerged, with at least an inch of oil above the top of the plant material. We use rice bran oil and sunflower oil as our primary carriers — both lightweight, skin-compatible, and free of common allergens. The oil must cover everything; any plant material exposed to air above the oil line can mold.
Step 5: Seal and label The jar is sealed tightly and labeled with the plant name, the oil used, and the date. This sounds obvious, but after six weeks, jars of similar-looking golden oil become difficult to distinguish without labels.
Step 6: Infuse The jar goes to a warm spot — our kitchen windowsill, which gets good morning light — and stays there for four to six weeks. Every morning, it gets a shake. Every few days, we check that the plant material is still fully submerged and that there are no signs of mold or off-smell.
Step 7: Strain After four to six weeks — when the oil has reached its full color and the plant material looks spent — we strain through a nut milk bag (or cheesecloth), squeezing the plant material to extract every last drop of infused oil. The spent plant material goes to the compost. The oil goes into a clean, labeled storage jar.
Step 8: Into the formula The finished infused oil becomes the carrier base for salves, balms, lip care, and body products. Everything that the plant had to give is now in the oil — and through the oil, in the finished product that eventually reaches your skin.
What You Can Infuse at Home
If this process appeals to you — and I hope it does — here are the botanicals I'd suggest starting with, all of which grow readily in the Pacific Northwest and are forgiving for beginners:
Calendula (Calendula officinalis) — the classic starting point. Easy to grow, easy to dry, produces a beautiful golden oil that is gentle enough for the most sensitive skin. Start here.
Plantain (Plantago major) — almost certainly growing in your yard right now, uninvited. Pull some leaves, dry them, infuse them. One of the most useful plants you're probably already ignoring.
Lavender (Lavandula angustifolia) — produces a delicate, aromatic infused oil that is lovely in facial care and body products. Use the flowers, fully dried.
Comfrey (Symphytum officinale) — less common, but deeply rewarding. Use the root or the leaf, fully dried. For external use on unbroken skin only.
Rose petals (Rosa spp.) — dried rose petals produce a subtly floral, skin-loving oil that is beautiful in lip care and facial products. Use petals that have not been treated with pesticides.
A Note on Patience
I want to close with something that I think about often when I'm shaking the jars on my windowsill.
We live in a culture that has largely lost its tolerance for waiting. We want results immediately — instant downloads, same-day delivery, overnight shipping. The idea of starting something today that won't be ready for six weeks feels almost countercultural.
But plants don't care about our timelines. They give what they give, at the pace they give it, and the quality of what you receive is directly related to the quality of the attention you bring and the time you allow.
There is a lesson in that, I think, that extends well beyond herbal oil infusions.
The jar on my windowsill will be ready when it's ready. And when it is, it will be worth the wait — as the best things always are.
— Briana, The Village Wisewoman, Renton, Washington
⚠️ Disclaimer: This post is for informational and educational purposes only and does not constitute medical advice. Comfrey is recommended for external use on unbroken skin only.
Shop products made with our slow-infused oils | Learn more about our formulation philosophy | Read next: Calendula — The Farm Flower That Does Everything