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.
Typically potted rosemary should be watered once a week in Summer and once every 2 weeks in the Spring and Fall.
Do not water rosemary in Winter as it is in a state of dormancy and additional watering increases the risk of root rot. Well draining soil is just as important for avoiding root rot.
How often you should water rosemary does depend on your climate and the conditions in your garden.
So keep reading for how to establish the optimal watering frequency for your rosemary plant in your garden and for the optimal well draining soil mix…
How Often to Water Rosemary
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.
To cope with 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 it is important to replicate the watering conditions of their native Mediterranean environment.
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 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 which influences how often to water your rosemary, such as:
- The size and material of the pot (small pots can dry out much quicker then 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 boarders or perhaps a raised bed. (Pots and raised bed 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.
Over watering is a far bigger risk to your rosemary then under watering so always err on the side of too dry rather then too damp.
If you rosemary is planted in a pot, feel the soil underneath through the drainage holes.
If the soil is damp then 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 then you can establish how often to water rosemary according to your conditions.
For raised beds or garden boarders rosemary often does not require watering when its fully established apart from times of pronounced drought.
Watering Rosemary in Winter
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.
Rosemary attains all the moisture it requires from the environment during Winter.
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.
Begin watering again in the Spring once very 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 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.
Whilst the variability of the climate, size of the pot, temperature and soil drainage can all have an impact on how often to water rosemary, the amount of water you should use should remain the same.
Water rosemary with a generous soak so that water trickles out the base of the pot. If your rosemary is planted in garden boarders 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 water also encourages the roots to grow and establish in the soil which further increases rosemary resistance to drought.
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 Over Watering Rosemary
The right soil for growing rosemary is perhaps more important then 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 moisture as this causes the leaves to turn brown or even black as a sign of stress.
(If your rosemary is turning brown the read my article for how to solve it).
Ordinary potting soil is likely to retain too much moisture for rosemary on its own but is appropriate if it is amended with horticultural sand or grit to recreates the sandy soil conditions of the rosemary native Mediterranean range.
Mix around 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 boarder or raised bed.
However 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 the rosemary and the preferred nutrient profile (rosemary requires low to medium fertility soil) of rosemary.
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.
(Read my article, best potting soil for rosemary).
Pots with Drainage Holes
Rosemary is a drought tolerant plant that does not like damp soil so it is essential that you plant rosemary in pots or containers with drainage holes in the base to allow excess water to escape away from the roots.
Also 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 are 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.
(Read my article, choosing the best pots for rosemary).
- 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.