How to Propagate Rosemary in August and Get Free New Plants

My grandmother always kept a bundle of dried rosemary hanging by the kitchen stove, and it smelled like warm pine and roasted potatoes. I tried to grow my own rosemary back then, but I killed my first three plants because I did not understand how they drank.

Once I figured out that late summer is the easiest window to start new plants from cuttings, I never bought another plastic pot of rosemary from the grocery store. It’s a simple process that takes about twenty minutes, and you’ll end up with a dozen new starts for next spring.

Here’s how I do it every August, without any fancy greenhouse equipment.

Why August is the Sweet Spot for Rosemary Cuttings

Many gardeners think spring is the only time to propagate herbs, but rosemary is different. By late summer, the new stems that grew in spring have started to mature. They aren’t soft and green anymore, but they haven’t turned into hard, brown wood either. Horticulturists call this stage semi-ripe wood.

These stems have just the right amount of energy to push out roots quickly, but they’re tough enough that they won’t rot the second they touch damp soil. I’ve tried propagating in June and in November, but my August batch always has the highest survival rate. It’s the perfect sweet spot before the autumn chill sets in.

If you’re already propagating other herbs, you might want to look at my guide on 10 plants to propagate from cuttings in August, which includes several woodier perennials.

August gives the young plants just enough time to develop a small root system before winter arrives. That means they’ll be ready to plant in the garden next spring.

The Bend Test: Finding the Perfect Stems

You can’t just snip any branch and expect it to grow. If the stem is too young and green, it will turn to mush in the soil. If it is too old and grey, it may sit there for months without producing a single root.

I use the bend test to find the right wood. Grasp a rosemary branch about 5 inches (13 cm) down from the tip and bend it gently. If it bends like soft spaghetti, it’s too young. If it cracks or refuses to bend at all, it’s too woody.

You’re looking for a stem that resists slightly, then bends with a springy feel. That’s the semi-ripe zone.

Warning: Avoid stems with flowers or flower buds, because the cutting will waste its limited energy trying to bloom instead of making roots. I also take cuttings early in the morning, when the parent plant is full of water after the cool night and the stems have the best possible start.

Setting Up the Pots and Soil Mix

Rosemary hates wet feet, and this is even more critical for cuttings. Standard potting mix holds too much water, which suffocates the new root buds before they can break through the bark. I mix my own propagation soil, and it’s very lean.

I use two parts peat-free potting compost to one part horticultural perlite. The perlite keeps the mix light and airy, allowing oxygen to reach the cut base. If you don’t have perlite, clean horticultural sand works just as well.

Fill your pots and press the mix down gently to remove large air pockets. Water the pot thoroughly before you insert the cuttings. The soil should feel like a wrung-out sponge, not a puddle. This mimics the dry, rocky soils of the Mediterranean where rosemary grows wild.

If you are interested in similar soil prep rules, you can check my article on how and when to prune lavender, which covers the drainage needs of Mediterranean herbs.

Taking and Prepping Your Cuttings

Once your pots are ready, it’s time to cut. I use clean pruners wiped with rubbing alcohol to prevent spreading disease. Cut a 5-inch (13 cm) stem just below a leaf node, which is the bump where leaves attach.

This area contains a high concentration of growth hormones, making it the fastest place for roots to form. Make your cut at a 45-degree angle. This increases the surface area at the bottom, giving the stem more space to absorb water and push out roots.

Next, strip the leaves off the bottom 2 inches (5 cm) of the stem. Just pinch the stem between your fingers and pull downward. The leaves should pop off easily.

Leaving those lower leaves on the stem is a recipe for rot because they will decay when buried in damp soil. You should have a clean, bare stem at the bottom and a small tuft of leaves at the top.

Settling Them In and Creating the Greenhouse Effect

To plant the cuttings, don’t just shove them into the soil. Rough soil particles can scrape the outer bark and damage delicate growth cells. Instead, use a pencil or small twig to make holes in the prepared soil mix.

Slide each bare stem into a hole until the lowest leaves sit just above the soil line, then firm the soil gently around it. You can place four or five cuttings in a single 4-inch (10 cm) pot, as long as their leaves don’t touch.

Because the cuttings have no roots, they lose moisture through their leaves faster than they can replace it. Cover the pot with a clear plastic bag, using wooden skewers to keep the plastic away from the foliage, and secure it around the rim with a rubber band.

Tip: Vent the bag for about ten minutes each day to improve airflow and prevent mold. Keep the pot in a warm place with bright, indirect sunlight, and avoid direct window light because the plastic can trap heat and cook the cuttings.

The Water-to-Soil Trap (And How to Avoid It)

I see many gardeners on Reddit who root their rosemary cuttings in a glass of water on their windowsill. It looks beautiful, and it’s exciting to see those white root threads develop. But there’s a trap.

Roots grown in water are structurally different from roots grown in soil. Water roots are fragile and lack the tiny root hairs needed to absorb nutrients from soil particles. When you transplant water-rooted cuttings into soil, they often go into shock and die within a few days. That’s why I prefer starting them directly in a soil mix.

If you do root them in water, you must acclimate them slowly. Add a spoonful of soil to the water jar every day over a week until the water turns into thin mud. This forces the roots to adapt before you pot them up.

According to the Penn State Extension, stem cuttings rooted directly in a porous medium develop stronger root systems that transition better to garden conditions.

Getting Your Babies Through Their First Winter

By late September, your cuttings should have a small clump of roots, but they still aren’t tough enough to survive a cold winter outdoors. If you live in Zone 8 or warmer, you may be able to leave them in a sheltered spot outside. For everyone else, they should spend the winter indoors.

Move the pots to a cool windowsill in a room that stays around 55°F to 60°F (13°C to 15°C). They won’t need much water during winter because their growth slows down. I water mine only when the top inch of soil feels completely dry.

Keep the young plants away from drafts and dry heating vents. In spring, once the threat of hard frost has passed, gradually harden them off before planting them in the garden.

Give It Six Weeks

The hardest part of propagating rosemary is doing nothing. It takes four to six weeks for roots to establish, and you won’t see any new growth on top during this time. Don’t pull on the stems to check if they are rooting, because you will tear the microscopic root hairs.

Just keep the soil damp, vent the plastic bag daily, and wait. By October, you’ll see tiny green tips emerging from the top, and that’s your sign of success.

— Anh