When and How to Prune Rosemary Plants
Are you ready to prune your rosemary this season, but aren't quite sure where to start? Rosemary is a fairly forgiving plant, but aggressive pruning can harm growth. In this article, gardening expert Logan Hailey outlines how to prune rosemary by following six simple steps.
Rosemary is a drought-tolerant Mediterranean perennial herb that provides a lot of fragrance and beauty in exchange for very little maintenance. The only thing your rosemary consistently demands is annual or twice-yearly pruning.
This quick haircut ensures that your rosemary bush stays shapely and attractive. Pruning also prevents woodiness, maintains air flow to prevent disease, and encourages new flushes of rosemary growth.
If you feel a little uneasy about taking the pruners or hedge trimmers to your rosemary bush, here are six easy steps to make rosemary pruning a breeze.
Thankfully, this plant is very forgiving, and you are unlikely to damage your rosemary shrub if you follow these simple instructions.
Rosemary can be pruned once or twice a year. The best time to prune is in the late spring or early summer after its flowers begin to fade. This may encourage new blooms, but the timing is also important because it gives new growth time to harden off before autumn frosts.
Optionally, you can prune again in the fall 6-8 weeks before the expected frost date. A second pruning is only necessary in regions where rosemary grows exceptionally quickly or if you need to significantly reduce the size of your rosemary.
Plants that have become overgrown or leggy should be gradually pruned by cutting back about one-third of the plant every 3-4 months during the growing season.
Outdoor rosemary thrives in zones 7-11, so March-May are usually the best time to prune. Indoor container rosemary plants can be pruned any time during the spring.
To avoid stunting or killing a rosemary bush, never remove more than a third of its growth at one time. Cutting too far back into the woody parts of the rosemary plant could kill it.
Just like its cousin lavender, rosemary shrubs should only be pruned down to a few inches above the woody central branches. The bush needs enough leaves and branches to sustain photosynthesis and produce enough energy to keep growing.
A fresh haircut for your rosemary plant benefits plant health and your garden aesthetic. Pruning can help:
|New Growth||Like lavender, rosemary only grows new leaves on pliable, green stems. Cutting off the tips encourages the stems to branch out and grow into multiple stems rather than one woody stem. The result is a bushier, more attractive plant.|
|Root Establishment||Pruning rosemary encourages it to funnel energy into the roots. This is especially important in the early stages of growth and the weeks leading up to winter dormancy.|
|Disease Prevention||Pruning encourages airflow between rosemary branches, making pathogens less likely to take hold. This is particularly important in extra humid climates where powdery mildew and botrytis often attack rosemary.|
|Prevent Woodiness||Rosemary’s fragrant needles and flowers cannot grow on old crowns or trunks. Pruning encourages the plant to remain pliable and green rather than woody and brown.|
|Prevent Leggy Growth||Without pruning, rosemary stems can get out of control. Leggy growth leads to floppy stems, weak plants, and a greater risk of damage in heavy winds.|
|Maintain Shape||Whether you prefer a cone-shaped bush, gumdrop shrub, pathway border, or a large hedge, rosemary can be pruned into nearly any shape you desire.|
Pruning Rosemary in 6 Easy Steps
Once rosemary’s purple spring flowers have begun to fade, it’s time to get cutting. You can schedule your pruning at the same time as a big herb harvest and processing party.
Consider bundling and hanging your trimmings to dry so you can use them as seasonings later in the year. This is also a great time to take rosemary cuttings!
Step 1: Sharpen and Sanitize Tools
It’s important to start with very sharp, clean pruners, loppers, pruning shears, or garden scissors. For shaping hedges or topiaries, electric hedge trimmers will make your job much easier.
Ragged cuts can make your plant more susceptible to pests and diseases, so be sure those blades are sharp!
Wipe the blades with rubbing alcohol or spray with a diluted bleach solution before beginning. If you have had any issues with diseases on your rosemary plants, it’s also best to sanitize between plants. Believe it or not, fungal spores can easily spread via pruning blades!
Step 2: Remove Dead & Dying Branches
Examine your rosemary plant for withered flowers, brown leaves, broken branches, diseased areas, or any other dead plant material.
Many of these dying shoots may be located near the base of the plant, especially if your rosemary is growing in poorly drained soil. Remove these branches first, and if there are any signs of fungal growth, throw them in the trash rather than the compost.
Take care to cleanly cut any broken branches from just below the split or frayed point. This will ensure that the plant does not break further down or cause damage to the central trunk of the shrub.
Step 3: Locate Pliable New Growth
Before you start any major cutting, step back for a moment and look at the entire shrub so you can identify the different types of growth.
Notice there are three main parts of the plant:
- Woody old growth: This is the dark brown, hard material near the base and center of the plant. Woody stems will have little to no leaves growing from them. Avoid cutting into the woody growth.
- Mature growth: The dark green leaves and semi-pliable stems are last season’s growth. This is the middle portion of the shrub that includes the bulk of the plant’s leaves. They often have the majority of the plant’s flowers. Avoid pruning more than one-third of this growth away.
- New growth: The bright yellow-green tips of the rosemary are this spring’s fresh new growth. These tips are extremely soft and young. New growth tips are the best for cuttings.
Maintain awareness of these different stem plant sections as you prune. It’s also best to spread the leaves apart to check the center “crown” of your rosemary plant.
This is the central stem or bundle of stems (similar to a tree’s trunk) where the plant anchors into the ground. Avoid cutting it at all costs.
Step 4: Cut Back One-third of Growth
Finally, you can start the haircut process! Imagine the plant height divided into thirds. Grab a handful of branches at a time and cut back up to one-third of the upper stem length.
Eliminating large amounts of foliage is considered “rejuvenation pruning” because it eliminates old leaves and triggers the plant to enter a new growth cycle. This is particularly helpful if your rosemary is leggy, overgrown, or damaged from harsh weather.
Remember that the majority of your cuts will be made in that middle “mature growth” section. The stems should not be super hard to cut into.
Don’t prune into the woody portion. Leave behind a minimum of 4-6 inches of leafy growth on the plant. If you remove too much foliage, it won’t have enough leaves to photosynthesize and regenerate.
If your rosemary is still young and tender, stick to pruning the upper 3-6 inches. Removing the tips will encourage more branching and bushy growth as the plant matures.
When pruning young rosemary shrubs, take more care to cut stems right at the point of a stem joint or a low set of leaves.
The point where two leaves emerge from the stem is called a node. Nodes are where the plant has the most meristematic tissue that allows it to branch out and develop new growth. Cutting at the node is also important if you plan to root your rosemary prunings as cuttings.
For large, older shrubs, you don’t need to be as particular about where you cut. You can use hedge trimmers or large loppers to focus more on the overall shape.
Step 5: Shape as Desired
Rosemary shrubs are eager to grow in any shape you prefer. You can make the plant a neat, manicured gumdrop, or you can let it bush out into a lush shrub.
- For a hedge, simply cut straight across the top and straight down the sides.
- For a rounded shape, you may cut shorter on the sides and keep the central stems longer so the plant arcs up.
As you cut, be mindful of the shape you are creating. Take a step back every few minutes to ensure you’re still on track.
Don’t forget about the practical part of pruning! If your rosemary is overgrowing a nearby plant or collapsing into the pathway, you will definitely want to prune back those parts to keep the plant in its zone.
Step 6: Avoid Cutting into Woody Branches
Just like its lavender cousin, rosemary is very sensitive about its woody branches. The hardwood forms the “core” or “crown” of the plant and helps it to survive harsh weather. Cutting into the wood could jeopardize your plant’s health and expose it to a range of pest or disease issues.
If you notice that your pruners are getting extremely hard to squeeze, it’s probably because you’re cutting into a woody branch that is best left alone.
Stay focused on the pliable stems, and always be sure that there are several inches of leafy growth left behind. This plant is extremely resilient to pruning as long as you leave its woody crown in peace.
If you have pruned any semi-woody landscaping plants like lavender or oregano, then pruning rosemary will be a breeze. This herb is extremely robust and enjoys its yearly haircut.
When in doubt, remove a little less green growth and see how the plant performs. If you notice it getting leggy, you’ll know that you need to cut back more next year. Just remember, rosemary wood prefers to be left alone!