This page is mostly about propagation, because that is what rosemary is mostly searched for and because seed is the wrong way to get a plant. Rosemary seed germinates slowly and unevenly and gives a variable seedling; a cutting roots in weeks and copies a plant you have already tasted.
The quick facts table above carries almost no dates or figures for this crop, and the reason sits in each row: rosemary is grown from cuttings rather than sown, so a frost-offset sowing date does not describe it.
Why cuttings rather than seed
Rosemary can be grown from seed. It is just a poor idea, and it is worth saying why rather than leaving it as received wisdom.
- Germination is slow and erratic. A low proportion of seed comes up, over a long and unpredictable period, which makes a tray hard to manage.
- Seedlings are slow. A rosemary from seed takes a long time to become a plant you can pick from. A rooted cutting is ahead of it from the start.
- Seed does not copy the parent. Rosemary varieties differ in habit, flavour and how much cold and wet they tolerate. Seedlings are variable, so you cannot know what you have until it is grown. A cutting is genetically the parent plant.
That last point is the one that matters most in a cold or wet garden. If a neighbour has a rosemary that has survived ten winters where yours have died, a cutting from it is worth more than any seed packet — you are copying a plant that has already proved itself in your conditions.
How to grow rosemary from cuttings
Penn State gives a full protocol for this, and it is worth following exactly, because two of its steps are the ones home propagators skip and they are the two that decide how fast a cutting roots. The steps are in order.
1. Cut a six-inch stem tip. Take a 6-inch section of stem tip from a healthy plant, with clean, sharp snips. Take several — not every cutting roots, and a handful costs no more effort than one.
2. Strip the lower leaves. Pull or cut the leaves off the lower part of each cutting, leaving the top ones. Any leaf buried in the mix rots, and that rot spreads to the stem.
3. Dip the base in rooting hormone. This is the first commonly skipped step, and it is in the published method rather than optional decoration.
4. Use a sterile, well-aerated soilless mix. Not garden compost, and not a moisture-retentive potting compost. Sterile matters because rot is the main way a cutting is lost, and a cutting has no roots yet to defend itself. Well-aerated matters for the same reason. Small pots are better than large ones.
5. Insert the cuttings and give them bottom heat. Push each one in so the stripped part is buried and the remaining leaves sit clear of the surface, then firm the mix gently — a cutting that wobbles will not make contact. Then the second skipped step: bottom heat at 70 to 75°F. This is what turns rooting from a matter of weeks into a matter of days, and it is the single biggest difference between the published method and the usual windowsill attempt.
6. Expect rooting in ten to twenty days. That is Penn State's window at that temperature. Check by tugging a cutting very gently; resistance means it has rooted, and firm new growth at the tip is the other sign. Without bottom heat it takes considerably longer, so judge by the tug rather than the calendar. Expect a proportion never to root.
7. Transplant out into full sun. Once rooted, move each cutting on and plant out into full sun at the spacing in the table above. Keep a young plant sheltered through its first winter before it has to take one outdoors — a rooted cutting is far more vulnerable to cold and wet than an established plant, and this is where most home-propagated rosemary is lost.
Rosemary will also root in water on a windowsill. It is the easiest version and the least reliable: water-rooted cuttings transfer to soil less successfully than ones rooted in a mix, and there is no bottom heat to speed them along.
Sun, shade and position
Rosemary wants the sunniest, most open position you have, with air moving around it. This is not only about growth — sun and wind dry the foliage and the soil surface, and a plant that dries out between waterings is a plant that hardens off and survives winter.
It will grow in part shade, and it will not look right: longer, thinner stems, sparse foliage, weaker scent, and a much higher chance of rot. If the only spot available is shaded for half the day, grow it in a pot you can move into the light rather than planting it out there.
Cold, wet and what an established plant survives
Penn State classes rosemary as a tender perennial evergreen shrub, and that is the honest starting point: it stays outdoors year-round only where winters are mild. Elsewhere it is grown as an annual, or kept in a pot and brought indoors — Penn State says two to three weeks before the first frost, which gives it time to adjust rather than being moved in a panic on the night.
Within that, hardiness is usually discussed as a single number, and that framing is the reason people lose plants. Cold on its own is rarely the killer. Cold plus wet, heavy soil is.
The same variety, in the same winter, in the same garden, will come through in gritty, sharply drained ground and die in a cold, wet clay bed. Water sitting around the roots through a cold spell rots them, and the plant browns off from the base. So the useful question about a position is not how low the temperature drops, but where the water goes after heavy rain.
Three things shift the odds, none of them a temperature:
- Drainage, which matters more than everything else together. On heavy ground, plant on a mound, in a raised bed, or in a pot. What to fill raised garden beds with covers the mix; for rosemary, push it towards the coarse and gritty end.
- Variety. Named varieties are sold specifically for cold tolerance, and the nursery label is the place to check — neither publication behind this page compares one variety with another, so we do not either.
- Age. An established plant with a woody frame and a deep root system is in a different position from a rooted cutting in its first year. Give a young plant shelter for its first winter.
Where winter is genuinely too much, the practical answer is a pot that moves somewhere bright, unheated and frost-free, kept only just moist. A rosemary kept warm and watered indoors all winter usually does worse than one kept cold and nearly dry.
Growing rosemary in a pot
A pot is often the best way to grow rosemary, because it puts the drainage entirely under your control.
The mix. Light and well-drained, which is what both publications ask for: about a third coarse grit, perlite or sharp sand mixed into ordinary compost. Penn State puts rosemary's soil pH at 6.5 to 7.0, and UGA notes it as one of the herbs that will take the alkaline end of the herb range rather than wanting acid ground. A rich, moisture-retentive potting compost is the single most common reason a potted rosemary dies, and it dies at the roots long before the foliage shows it.
The pot. Make sure the drainage holes are open, stand it on feet or bricks so water actually leaves, and never leave it standing in a full saucer. Terracotta helps because it dries through its walls. Do not over-pot — a container far larger than the rootball holds a lot of wet mix the roots are not using.
Watering. Let the surface dry between waterings. A pot in summer sun needs water regularly and that is fine; what is fatal is a mix that never dries. Indoors, still humid air also invites powdery mildew, so give it some air movement.
The potting soil calculator works out how much mix a given pot or planter takes, and how much potting soil a container needs explains the units bags are sold in.
Feeding, pruning and picking
Feeding: very little. Rosemary grows on poor, thin soil in its native range and rich feeding produces soft growth that is more prone to rot and less strongly flavoured. Drainage is worth more attention than fertiliser.
Pruning: lightly, and not into bare wood. Like lavender, rosemary is reluctant to reshoot from old bare wood, so keep it in shape by trimming growth that still carries leaves rather than cutting hard into the brown frame. Trimming after flowering keeps a plant compact; an untrimmed one gradually becomes a sprawling, woody thing with the foliage all at the ends.
Picking is pruning. Take sprigs from the tips through the season and the plant stays bushy. Rosemary is evergreen, so there is no season when there is nothing to pick, though growth effectively stops in the coldest months and a plant should not be stripped then.
Spacing is 24 to 36 inches, and the range is a real disagreement rather than vagueness: UGA gives 2 to 3 feet and Penn State 2 feet, so the table spans both rather than picking one. The plant spacing calculator turns it into plant counts for a bed.
Give it the room, because rosemary gets large. Penn State puts a mature plant at 2 to 6 feet tall and 2 to 6 feet wide — a considerably bigger thing than the pot on the garden centre bench suggests, and the usual reason one ends up crowding its neighbours.
Rosemary companion plants
As with lavender, the useful test for a rosemary companion is not a traditional pairing list but whether the neighbour wants the same conditions. Rosemary needs sun, sharp drainage and poor soil, and it will be killed by the watering and feeding regime that a moisture-loving neighbour needs.
That makes the other woody Mediterranean herbs its natural companions: lavender, thyme and sage all share its requirements almost exactly, and a bed of those four can be managed as one. The soft herbs are the opposite case — basil, dill and parsley all want moisture and some feeding, so they belong in different ground.
Rosemary is also traditionally planted near brassicas, on the claim that its scent confuses cabbage moth and carrot fly. This is one of the weaker companion planting claims: the mechanism is plausible, the evidence is thin, and there is no cost to trying it. Does companion planting actually work sorts the well-supported mechanisms from the repeated ones. What is not in doubt is that rosemary in flower is worked hard by bees, and it flowers very early in the year when little else does.
Note the naming confusion while you are here: rosemary has been reclassified as Salvia rosmarinus, so it is now botanically a salvia. Lavender is not, and never was, despite being mistaken for one constantly.
Common problems
The cuttings rotted. Too wet, too enclosed, or leaves left on the buried part of the stem. Use a grittier mix, take the lid or bag off, and strip the lower leaves properly.
Nothing rooted at all. Wrong wood — too soft, or too old and brown. Take firm current-season growth, and take more cuttings than you need.
The plant browned from the base upwards. Root rot from wet ground, most likely over winter. Check where water sits in that spot before replanting.
Leggy, sparse growth with weak scent. Not enough light. Move it.
A white dusty coating on the leaves indoors. Powdery mildew, from still humid air. Improve air movement and space plants further apart.
Our other herb guides are basil, dill, parsley and lavender, and the full set is on the crop guides index.