Although overwatering is the primary cause of potted rosemary plants’ death, selecting the appropriate potting soil is equally crucial to maintaining an optimal watering schedule. If the rosemary’s roots are immersed in potting soil that holds a lot of moisture, it can lead to root rot, even if you water your rosemary correctly.
To grow rosemary successfully and achieve the best fragrance, it is essential to use potting soil that has good drainage, low moisture retention, and moderate fertility. The ideal potting mix for rosemary should consist of two-thirds compost and one-third horticultural sand.
Continuing to read will provide you with information on how to produce the optimal potting mix, reasons for steering clear of peat moss, and ways to prevent typical errors when potting rosemary.
Criteria for Good Potting Soil for Rosemary Plants
- The ideal soil for growing rosemary in pots should be well-draining and porous, preventing water retention.
- Efficient root respiration is facilitated by an aerated soil structure, which is preferred by rosemary as it does not thrive in compacted soil.
- The soil should have medium to low fertility.
- High inorganic matter soil is necessary for rosemary to thrive, which resembles the sandy and gritty soils of its natural habitat.
Rosemary is a herb that hails from the Mediterranean area of Southern Europe, where it can be found growing naturally on hillsides in Spain, Portugal and France.
Rosemary grows well on hillsides and prefers soils that are low in nutrients, drain quickly, and have a sandy or gritty texture, which holds less moisture.
Slopes naturally provide great drainage and the coarse, aerated, and permeable soils guarantee that any extra moisture does not remain in the soil around the roots, which helps to prevent root rot, a common issue for rosemary growers.
Soils that hold a lot of moisture, such as amended compost with wetting agents or clay soils, can increase the risk of fungal disease affecting your rosemary, which can cause its leaves to turn yellow, brown, or even black, leading to its death.
Check out my article, reviving a wilting rosemary plant, for more information.
Planting rosemary in soil that is nutrient-rich, such as loam soil, compost with added fertilizers, or manure-amended soil high in nitrogen, goes against the low fertility, gritty, sandy soil conditions that rosemary has adapted to.
Planting rosemary in soil that is rich in nutrients can result in droopy growth, while higher levels of nitrogen can decrease the concentration of essential oils responsible for the herb’s unique aroma and flavor. As a result, planting rosemary in fertile soil may lead to a less flavorful and fragrant plant with fewer flowers.
Rosemary thrives in pots and containers due to their ideal drainage conditions, which replicate the natural well-draining environment found on hillsides.
To maintain the health of potted rosemary in your garden, it is crucial to imitate the well-draining soil conditions of the Mediterranean region.
How to Create the Perfect Potting Soil for Rosemary
Although a Mediterranean climate is not necessary for growing rosemary, it is possible to replicate the soil conditions.
For optimal growth of rosemary in pots, it is crucial to replicate the sandy and gritty soil conditions with medium to low fertility found in its original Mediterranean habitat.
To enhance the quality of soil for growing rosemary in pots, it is possible to improve regular multipurpose compost by adding coarse horticultural sand or grit.
Horticultural sand and grit can replicate the inorganic component of rosemary’s natural soil, which is typically sandy and stony. This helps to promote efficient drainage and a porous structure, allowing for adequate oxygen in the soil that is crucial for root respiration. Additionally, it prevents soil compaction that could hinder drainage.
If you want to recreate the ideal soil for rosemary in pots, it is recommended to combine 70% compost with at least 30% horticultural sand or grit, which mimics the Mediterranean soil.
Having an abundance of sand or grit is always preferable to having too little, as the sand can help prevent root rot, which is the most frequent cause of a wilting rosemary plant.
If you reside in a region with more precipitation, like the Pacific North West or Northern Europe, it is advisable to incorporate a greater amount of sand or grit into the soil.
Ensuring proper drainage is crucial for rosemary as it has evolved to withstand dry conditions and soil with low moisture content.
Incorporating more sand or grit into the potting mix can help counteract the effects of wetter climates, and your rosemary should thrive once it is in its preferred well-draining environment.
After consulting with lavender, rosemary, and Mediterranean herb growers in Washington and Oregon, it has been suggested that the ideal potting mix for growing rosemary in a rainy climate is a combination of 50% horticultural sand or grit and 50% multipurpose compost, which provides the necessary drainage balance.
Sand and grit have an additional crucial function in regulating the appropriate level of soil fertility for rosemary.
Contrary to expectations, rosemary grows well in soils with lower fertility levels, resulting in the production of leaves with the best aroma and flavor, as well as more flowers.
Sand and grit are not significant sources of nutrients for the soil. They play a role in balancing the fertility of the compost in your potting soil, which is crucial to replicate the same level of soil fertility found in the Mediterranean region, ensuring that your rosemary plant has optimal aroma and flavor.
Rosemary can obtain all the necessary nutrients from a potting mix that contains grit and compost.
Avoid this mistake!
Using ordinary beach sand instead of horticultural sand in your rosemary potting mix is not recommended.
Horticultural sand has a coarser texture and larger particle size compared to regular beach sand, which consists of finer grains.
The larger size of horticultural sands enables better aeration in the soil and facilitates efficient drainage of water.
Small beach sand particles can result in a soil mixture that drains slowly and has a less porous structure, which can also prevent the entry of oxygen.
You can typically find horticultural sand, grit, or perlite at affordable prices in garden centers or on Amazon.
Check out my article, selecting the best soil for rosemary in pots).
Avoid Amending Rosemary Potting Soil with Peat Moss
Avoiding peat moss is recommended for growing rosemary in pots because it hardens in full sun, which is required by the plant, and becomes hydrophobic when dry, leading to water running off the soil surface without reaching the roots.
Rosemary can survive drought, but if the soil surface is deflecting water, the roots won’t be able to absorb moisture, which can lead to dieback.
It is important to choose a potting mix for rosemary that is clearly labelled as peat-free compost or potting soil.
It is not recommended to use compost with wetting agents or added fertilizer for potting rosemary as these characteristics do not align with the preferred soil conditions of the plant, in addition to avoiding high peat content.
The best potting mix for rosemary in pots is a regular multi-purpose compost that has been improved with sand or grit.
It is essential to understand when to water rosemary in containers to ensure the ideal balance of moisture is maintained. To learn more about the best practices for watering, read my article how to water rosemary.
Potting Soil pH for Rosemary
Rosemary is native to areas with calcareous soils, which are usually alkaline in terms of pH. The optimal pH range for rosemary is 6-7.5, which is slightly acidic, neutral, and slightly alkaline. However, some varieties of rosemary can tolerate a pH range of 4.3-8.3.
Most potting soils and composts available in the market have a pH range of 6-7.5, which is ideal for growing plants in pots. However, it is recommended to avoid using ericaceous soils as they are specifically designed for plants like camellias that require higher levels of acidity.
It is unnecessary to modify the soil with lime or any other substance that increases the pH level to alkaline, as it may cause harm to the rosemary if added excessively, although it may not necessarily be detrimental.
Check out my article on the best soil for rosemary in pots).
Key Takeaways:
- Rosemary thrives in potting soil that is poor, dry, and sandy, with low fertility. To recreate the ideal growing conditions of its native Mediterranean environment, the best potting mix for rosemary should consist of two thirds compost and one third horticultural sand.
- To prevent root rot, it is advisable to refrain from using potting soils that contain fertilizers or those that have high moisture retention when planting rosemary in pots.
- Horticultural sand or grit, with its larger particle size, imitates the porous and aerated soil structure that rosemary thrives in, facilitating excellent drainage and minimizing the possibility of root rot.
- Rosemary can thrive in soils with varying pH levels, including acidic, neutral, and alkaline. Lime amendment is unnecessary for compost and sand potting mixes, as rosemary can grow successfully within the typical soil pH range.