The size of the pot where your rosemary plant is placed affects the health and growth of your rosemary significantly. Choose a too large (too early), and you risk root-rot, choose a too-small one, and your rosemary will stop growing. Hence, what’s best?
The ideal size for medium-size grown rosemary (70-80cm tall) plant is a 14 inches diameter (35.5 cm) pot at least 10-12 inches (25 to 30cm) deep. It is not necessary neither recommended to start with such a size planter. The size can be increased over time in case the initial planter is not large enough.
Hence, what should you do with your rosemary? Which planter should you use and which material to adopt.
Can rosemary grow in a pot? Yes, it can be grown successfully in a container if the planter is of the right size, and the environmental conditions like temperature, humidity, and light are close to the ones of its native area (Mediterranean).
Regarding the planter, the volume of the pot for your rosemary defines two critical features:
- The volume of growing medium: the more growing medium, the larger amount of nutrients the plant has access to;
- The root length: each plant develops roots of different lengths. However, some of them are relatively shallow and do not need a depth pot (like mint). In contrast, others like rosemary can have roots as depth as 24 inches (more often 12 inches) after a few years, as discussed by the University of California here. That’s why it is advisable to have at least 12inches depth (even if 10 inches is fine)
Here you can find a good looking pot, quite inexpensive given its size on Amazon.
If you did not have your 1+ year rosemary in a 14inches, the chances are that, to promote growth, you need to upgrade to a large pot. Roughly every year (depending on the light conditions and growth), rosemary ideally should be moved to a larger pot if the initial one was not large enough.
Here’s the catch
A rosemary pot should increase in size each time you repot it if you intend to grow the plant larger than it is. However, rosemary can be repotted into the same pot, or another of the same size, as long as the root system is trimmed (here be careful, do not cut it more than a third). Most small indoor rosemary plants can survive in a 35.5 cm (14 in) diameter pot with just yearly root maintenance.
A larger pot allows the root system to branch as the herb grows, accessing more nutrients in the soil. Once the root system of a rosemary plant reaches the bottom and edges of a pot, it needs to be repotted.
Place your rosemary in full sun if possible, by a large south-facing window. Rosemary requires decent airflow— a cool, dry, and sunny space with consistent air movement is the best place for a rosemary pot. However, not all of those conditions are necessary to grow rosemary successfully. For more information and rosemary trouble-shooting, read here.
For rosemary seedlings (around a millimeter size), you do not need (neither is advised) a big planter. Indeed, all the seedling starter kits (or container of similar size like a plastic cup) will do the job like the one shown below on Amazon.
They have square cells of around 4X4cm and 5 to 6 cm depth. Your seedlings need space to develop those first roots that might be even longer than the seedling itself. Remember, seeds will take 14 to 30 days to germinate and they should be kept at 15-18C (60-65 F) while sprouting.
Due to its origins as a Mediterranean plant, used to arid and rocky conditions, rosemary prefers a terracotta pot over plastic. Terracotta is naturally porous, allowing for air and water to pass through to the soil, or out of it. The clay in the pot absorbs some moisture from the soil, mimicking the more arid climate that rosemary prefers.
Remember: for any herb like rosemary that prefers steady airflow and drier soil, a clay pot will be a better choice. However, if you do not find a terracotta pot (or too expensive), you can also grow rosemary successfully in a plastic one (I did as well). In such a case, you just need to remember to water less than you would like given that plastic trap moisture more effectively than clay. Remember to “test the soil” by sticking your finger a few cms below the surface to check if it is moist or arid if moist; no water is needed).
Rosemary requires a very well-draining pot. This means:
- The rosemary planter must have drainage holes: rosemary is an herb that will not tolerate long-lasting wet roots. This common issue indeed causes many problems like rosemary purple leaves. That’s why it is not acceptable not to have drainage holes. Indeed, the water and moisture will get trapped for longer, leaving the roots to high risk of rotting. Most terracotta pots have a large circular hole at the bottom, which works well for rosemary. Remember to place a tray beneath the pot so that water drains slowly.
- The wet saucer: there should be no water left in the dish beneath the pot after watering. Indeed, if this is the case, such water will continuously be in contact with the bottom part of the soil. Not only it is a problem for the very deep roots (in contact with it) but also for the middle ones. Indeed, the soil acts like a sponge sucking water from the lower level if present.
- Do not place rocks or pebbles at the bottom of the planter. This will reduce the dry soil area— making less room for dry plant roots. This, in turn, will increase the time the roots will be in contact with water allowing some type of bacteria to thrive and rot the roots. The idea that rocks increase the drainage of the soil is false and can harm the plant.
Here a kick to improve your rosemary planter.
One strategy for maintaining humidity around the rosemary plant while not making the roots damp is to fill the tray beneath the pot with gravel and water. The gravel will keep the pot elevated, and the root system out of the water, while the proximity to the water will maintain moisture around the plant, mimicking the Mediterranean climate. For a step by step guide to this strategy, watch the video linked below.
Pots that are too small inhibit rosemary growth. It is essential to move your rosemary plant to a larger pot. An increase of 5 cm (2 in) in diameter is typica, every year at least (if your pot is not already at the large size). However, a plant can be maintained in a small pot, and be kept in the same pot over a long period, with the right repotting tactic. As long as the root system is cut back regularly, the rosemary plant will not become root-bound. For guidance on how to repot rosemary, check the good video below.
When a rosemary plant is left in one pot too long, the root system fills the space. In other words, the rosemary becomes root bound. A pot filled with roots restricts the rosemary’s ability to absorb water and nutrients from its environment, and stunts growth.
Removing around a third of the roots (5 cm for grown plants) from the bottom, cutting up the sides, and refreshing the soil is the best way to prevent a root-bound plant.
Moreover, the potting soil, which has become trapped within the root system, has been heavily exploited loosing most of its nutrition value. In general, this happens after six months if no further fertilizer is added.
Something I want you to remember
After chatting with some of my readers, this disclaimer is needed. The size I suggested here is the one that, based on my experience and those of other gardeners, is the best for long term growth. However, gardening, as you might know, is not an exact science as there are countless types of rosemary. However, this article aims to provide a general rule that, most of the time, will guarantee success if the basic (watering and sunlight) are checked. Good luck with your rosemary!
Where does rosemary grow best? Rosemary is native of the Mediterranean costs where, large rocky soil area, moist from the sea, and long hours of sunlight (6 to 8 daily), are the conditions for its maximum growth. Any area where most of these conditions can be met (either outdoor or indoor) are those that will make the rosemary thrive.
Where to find a rosemary plant? Rosemary plants are sold in supermarkets and big shops in the herb and spice section. Although they are meant to be used in the kitchen as a condiment, they can easily be transplanted in a larger planter for growth. If potted rosemary is not available, then rosemary stems (sold in small plastic bags) can still be propagated. For the latter, to increase the chances of success, it is suggested to use root hormones, or just attempt to propagate many stems at the same time.
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