I love to cook with rosemary, which is one of my favorite perennial herbs! However, I learned early on in my gardening career that it is critical to get the watering right when it comes to growing rosemary.
I had one plant succumb to overwatering when I first started which was a combination of me watering too often AND planting my rosemary in a potting soil that retained too much moisture! I had a lot to learn!
I now work at a garden center and prepare rosemary plants and other Mediterranean herbs for commercial sale, so I have learned first hand (and through some trial and error!) all the secrets and tips for watering so that the rosemary thrives!
In this post, I’ll share with you all of my research and techniques so that you know exactly how to water your rosemary according to the time of year and different conditions.
Are you in a rush? Here is my 2 sentence answer…
Rosemary is a drought-tolerant plant that requires the soil to dry out somewhat between bouts of watering to avoid root rot. Water rosemary with a good soaking so that water drains out the bottom of the pot, then let the soil dry before watering again.
In my experience, potted rosemary should typically be watered once a week in Summer and once every two weeks in Spring and Fall.
Typically I do not water my rosemary in winter as it is in dormancy, and additional watering increases the risk of root rot. I must emphasize that Well-draining soil is just as important for avoiding root rot.
However, we should take any universal watering advice with a grain of salt because, ultimately, I have found that how often you should water rosemary depends on your climate and the conditions in your garden.
So keep reading to learn how to establish the optimal watering frequency for your rosemary plant in your garden and the optimal well-draining soil mix.
How Often to Water Rosemary
As we mentioned earlier, our rosemary is a herb that has adapted to growing in the Mediterranean region of Europe where it thrives in full sun, sandy well–draining soils, and with infrequent rainfall.
We need to acknowledge that to cope with the Mediterranean full sun, rosemary is adapted to the arid environment, with only occasional rainfall, by growing thin needle-like leaves which reduce the surface area for water loss (transpiration).
As rosemary is so well adapted to growing in dry environments, they are very susceptible to problems associated with over-watering, which can cause root rot and the rosemary to turn brown or black.
(If your rosemary is turning black read my article for the solution).
To grow rosemary successfully at home, we need to recreate the watering conditions of their native Mediterranean environment.
Thankfully, I should note that Mediterranean herbs such as rosemary can grow outside of a Mediterranean climate if we get the watering right.
Rosemary requires the soil to dry out around the roots between bouts of watering so only water rosemary when the soil feels dry. If the rosemary its potted in suitably well draining soil, this means watering rosemary around once per week during Summer if there is no significant rainfall.
Typically, I watering potted rosemary once every 2 weeks in Spring or Fall is optimal for most climates and conditions.
It is important to note that the rate at which the soil dries can vary according to several factors that influence how often to water your rosemary, such as:
- The size and material of the pot (small pots can dry out much quicker than large pots. Metal or plastic pots also heat up quicker in the sun compared to clay or ceramic pots).
- Whether rosemary is in a pot or planted in garden borders or perhaps a raised bed. (Pots and raised beds have favorable drainage conditions for rosemary).
- Whether the rosemary is located in a windy open area (too much wind can dry the soil and sap moisture from the leaves).
- Humidity and temperature of the climate and weather conditions.
- The capacity of the soil to retain moisture (rosemary requires well-draining soil to avoid root rot).
It should be noted that rosemary prefers some air flow and breezy conditions as this replicates the natural growing conditions but also be aware that potted rosemary can dry out a little bit quicker in consistently windy areas.
Overwatering is a far bigger risk to your rosemary than underwatering so my advice is to always err on the side of too dry rather than too damp.
If your rosemary is planted in a pot, my method for establishing when it needs watering is to feel the soil underneath through the drainage holes.
If the soil is damp then I delay watering for a few day but if the soil feels mostly dry then this is the perfect time for watering.
Once you know how quickly your soil dries at the base of the pot, you can establish how often to water rosemary according to your conditions.
Pro Tip: I pick up my rosemary pots frequently to assess their weight. When I feel they are noticeably lighter, I know that the soil is dry and they need watering.
For raised beds or garden boarders, in my experience, rosemary often does not require watering when it’s fully established apart from times of pronounced drought.
I find that established rosemary has an extensive enough root system to find its own water. If you water them consistently when they are growing in garden beds then I’ve observed this increases the risk of root rot.
Watering Rosemary in Winter
As we discussed, in most climates, an outdoor potted rosemary does not require any watering during Winter.
During Winter, rosemary is dormant and is at greater risk of root rot due to cold damp soils that dry a lot slower due to lower temperatures.
The advice from the experts is that rosemary attains all the moisture it requires from the environment during Winter.
I’ve found that personally, In climates with higher rainfall, particularly in Winter, the requirement for well-draining soil amended with lots of sand or grit is much higher.
A higher proportion of sand to improve drainage and prevent the soil retaining too much moisture is the most effective way to mitigate the risk of root rot.
When I lived in the Pacific Northwest (which has a higher average annual rainfall), I experimented with different soil amendments, and from my testing, I found that as much as 50% horticultral grit to 50% compost achieved the right balance of moisture for my rosemary. The admittedly very high, gritty soil mix helped mitigate the threat of root rot as it allowed the excess rainfall to drain away easily.
Begin watering again in the Spring, once every 2 weeks, when temperatures have warmed up and the rosemary is actively growing.
(If your rosemary looks as though it is dying read my article on how to revive a dying rosemary plant for the solution).
How Much to Water Rosemary
Knowing how much to water rosemary is very important for growing success.
The best advice I received regarding watering rosemary is that Whilst the variability of the climate, size of the pot, temperature, and soil drainage can all impact how often rosemary is watered, the amount of water needed should remain the same.
You should always water rosemary with a generous soak so that water trickles out the base of the pot. If your rosemary is planted in garden borders or raised beds, ensure the soil has a good soak around the base of the plant.
This ensures the water effectively infiltrates the soil and reaches the roots so that they can uptake the moisture they require.
A generous watering also encourages the roots to grow and establish in the soil, which further increases rosemary’s resistance to drought. This is particularly important if you live in a hot and dry climate like me.
Avoid this common mistake! Watering too lightly causes the top inch or so of the soil to be moist, but the water does not reach the roots, and the rosemary can actually suffer drought stress.
Watering with a good soak followed by a period of drought replicates the ideal growing conditions in the rosemary native habitat.
(Read my article, how to care for rosemary in pots).
Well-Draining Soil to Avoid Overwatering Rosemary
For the many years I have grown my beloved rosemary plants, I have learned that The right soil for growing rosemary is perhaps more important than the watering schedule when it comes to keeping the plant healthy and avoiding root rot.
Rosemary does not tolerate its roots being sat in damp soil that retains lots of moisture as this causes the leaves to turn brown or even black as a sign of stress.
(If your rosemary is turning brown read my article for how to solve it).
I discovered through some trial and error that ordinary potting soil is likely to retain too much moisture for rosemary on its own, but if it is amended with horticultural sand or grit to recreate the sandy soil conditions of the rosemary native Mediterranean range.
I Mix atleast 1/3 sand or grit (by volume) with 2/3s potting soil or multipurpose compost for the optimal drainage conditions for rosemary. Sand and grit ensure a porous structure that allows water to drain effectively to avoid root rot.
This applies whether your rosemary is in a pot or whether you are planting rosemary in a garden border or raised bed.
However, I know I mentioned this earlier, but it is worth emphasizing that in colder climates with higher levels of rainfall, as much as 50% sand or grit to 50% compost may be necessary to ensure that water drains away from the roots as quickly as required for the rosemary to stay healthy.
This soil mix emulates the preferred drainage conditions of rosemary and the preferred nutrient profile (rosemary requires low to medium fertility soil).
I would also like to mention that nutrient-rich soil with lots of nitrogen promotes leggy growth that has a less pronounced aroma and inferior flavor of the leaves as this is contrary to the conditions to which the rosemary is adapted.
I have noticed this when rosemary has had added fertilizer or been planted in nutrient, rich soil amended with chicken manure (which is particularly high in nitrogen).
(Read my article, best potting soil for rosemary).
The Importance of Pots with Drainage Holes when It Comes to Watering
Rosemary is a drought-tolerant plant that does not like damp soil, so you must plant rosemary in pots or containers with drainage holes in the base to allow excess water to escape away from the roots.
Also remember we talked about watering, so that water trickles from the base of the pot is a good way to ensure that you have watered rosemary with enough water to reach the roots.
If rosemary is planted in pots without drainage holes the water pools around the roots, causing root rot and the plant dies back.
Water can still pool around the roots of potted rosemary because:
- Compacted soil or roots are blocking the drainage hole. If you notice water draining slowly from your potted rosemary, then check to ensure the drainage hole is clear.
- Saucers or trays underneath the pot. Saucers and trays catch excess water and can cause the soil to stay too damp for the rosemary roots, which promotes the conditions for root rot.
Pro Tip: I have a really good tip for you if you struggle with overwatering Mediterranean herbs. I have personally tested growing herbs such as rosemary in many different types of pots, and in my opinion, the best pots for growing rosemary are clay or terracotta pots, as they are breathable, which allows the soil to dry out more evenly between each bout of watering.
Since I have implemented this tip, I do not have any problems with overwatering!
Do you have any questions? Or any tips, tricks, or hacks for watering rosemary? Please leave a comment below; I’d love to hear them!!
(Read my article, choosing the best pots for rosemary).
Key Takeaways:
- Rosemary is a drought-resistant herb that should only be watered when the soil has dried out around the roots. Water rosemary with a generous soak so that excess water trickles out the base of the pot, then wait for the soil to dry again before watering.
- Typically, this means watering potted rosemary once a week in Summer and once every 2 weeks in Spring and Fall. Do not water rosemary in Winter to avoid root rot.
- Rosemary should be planted in soil that has been amended with horticultural sand or grit to improve drainage.
- Always plant rosemary in pots with drainage holes to allow excess water to escape and prevent root rot.