Tool

When to Plant Each of the 10 Medicinal Herbs

Every seed packet says “start indoors 6–8 weeks before last frost” and none of them tell you that three of these need a month in the refrigerator before that clock even starts. Put your frost date in and the arithmetic is done for you.

By Sohail Akhtar · Published 26 August 2026

Your last spring frost date

The average date of the last frost where you garden. If you do not know it, your local extension service or a neighbour who grows vegetables will. Everything below counts backwards from this one date.

Showing a mid-April default. Change it to your own date.

Your first job is Jan 7 — start cold stratification for lavender. Miss that one and it is the species most likely to disappoint you.

Seed starting schedule for the ten species, calculated from a last frost date of Apr 15
Species	What to do	When
CalendulaDirect sowing after frost works just as well and is less work.	Mar 11Sow indoors (or wait and direct sow)5 weeks before your last frost	Mar 11
	Apr 22Harden off and transplantAbout a week after your last frost date	Apr 22
ChicoryDeep taproot — direct sow only. Sow once soil has warmed.	Apr 15Direct sow outdoorsOnce frost has passed and soil has warmed	Apr 15
German ChamomileSurface sow. Needs light, and the surface must not dry out.	Mar 11Sow indoors (or wait and direct sow)5 weeks before your last frost	Mar 11
	Apr 22Harden off and transplantAbout a week after your last frost date	Apr 22
FeverfewSurface sow. Sown this early it usually flowers in year one.	Feb 25Sow indoors7 weeks before your last frost	Feb 25
	Apr 22Harden off and transplantAbout a week after your last frost date	Apr 22
YarrowSurface sow. Expect foliage only in year one.	Feb 25Sow indoors7 weeks before your last frost	Feb 25
YarrowSurface sow. Expect foliage only in year one.	Apr 22Harden off and transplantAbout a week after your last frost date	Apr 22
California PoppyTaproot — never transplant. Sow as soon as soil is workable; it prefers cool soil.	Mar 18Direct sow outdoorsAs soon as the soil is workable — it wants cool soil	Mar 18
Evening PrimroseBiennial. Direct sow; flowers in year two, not year one.	Apr 15Direct sow outdoorsOnce frost has passed and soil has warmed	Apr 15
MarshmallowStratify first, then sow. Wants consistently damp ground.	Jan 28Start cold stratification4 weeks in the refrigerator, barely damp	Jan 28
	Feb 25Sow indoors7 weeks before your last frost	Feb 25
	Apr 22Harden off and transplantAbout a week after your last frost date	Apr 22
EchinaceaStratify first. Flowers in year two.	Jan 28Start cold stratification4 weeks in the refrigerator, barely damp	Jan 28
	Feb 25Sow indoors7 weeks before your last frost	Feb 25
	Apr 22Harden off and transplantAbout a week after your last frost date	Apr 22
LavenderStratify first, surface sow, and expect slow uneven germination.	Jan 7Start cold stratification5 weeks in the refrigerator, barely damp	Jan 7
	Feb 11Sow indoors9 weeks before your last frost	Feb 11
	Apr 22Harden off and transplantAbout a week after your last frost date	Apr 22

These are general horticultural ranges for each species, not results from our own garden. Local conditions vary, and an average frost date is an average — a late cold snap beats any calendar.

Why the dates differ so much

The ten species in this collection do not share a schedule, and treating them as though they do is the most common way a first attempt goes wrong. There are three groups.

The three that need a refrigerator first

Evening Primrose, Marshmallow, Echinacea, Lavender all germinate erratically without a cold, moist period. That period happens before sowing, so it has to be added to the front of the schedule — which is why lavender ends up starting around fourteen weeks before your last frost while calendula only needs five.

If that sounds like a lot of planning, there is a shortcut: sow them outdoors in late autumn instead and let winter do it.

The three that must never be transplanted

Chicory, California Poppy, Evening Primrose form taproots almost immediately and resent being moved. Starting them in modules and planting them out is the usual cause of failure, so the calculator gives them a single direct-sowing date rather than an indoor start.

California poppy is the odd one: it wants cool soil, so it goes in earlier than everything else rather than later.

The four that are simply easy

Calendula, chamomile, feverfew and yarrow ask for nothing unusual. Sow, keep damp, wait. Two of them need light to germinate and so must be surface sown rather than buried, which the table notes.

Frequently asked questions

When should I start medicinal herb seeds indoors?

It depends entirely on the species and on your own last frost date. Lavender needs the longest run — roughly fourteen weeks before last frost once you allow for stratification. Echinacea and marshmallow need about eleven. Feverfew and yarrow want seven. Calendula and chamomile only need five. California poppy, chicory and evening primrose should not be started indoors at all.

Which of these seeds need cold stratification first?

Echinacea, lavender and marshmallow in practice, and evening primrose optionally. Stratification happens before sowing, so it has to be counted into the schedule — that is why the calculator puts a separate refrigerator date ahead of the sowing date for those species.

What is a last frost date and how do I find mine?

It is the average date of the last spring frost in your area, and almost all seed timing is expressed relative to it. Your local agricultural extension service publishes it, and most experienced vegetable growers nearby will know it. It is an average, not a guarantee — a late cold snap beats any calendar.

Which seeds should never be started indoors?

California poppy, chicory and evening primrose all form taproots early and resent being moved. Transplanting them is the single most common reason they fail. Sow them where they are to grow. California poppy in particular wants cool soil, so it goes in earlier than the others rather than later.

Is it too late to start if I have missed the date?

Usually not, for the easy ones. Calendula and chamomile flower within about eight weeks of sowing, so a late start still gives a season. The perennials — echinacea, yarrow, lavender, marshmallow — were not going to flower in year one anyway, so a few weeks late costs you very little. The one to be strict about is California poppy, which sulks in warm soil.

Can I sow any of these in autumn instead?

Yes, and for the stratifying species it is often the better option. Sowing echinacea, lavender or marshmallow outdoors in late autumn lets the real winter do the cold period, which is less work than the refrigerator and frequently gives better results. The trade-off is less control over where and when seedlings appear.