Rosemary Bonsai Care Guide
Rosmarinus officinalis is Latin for "dew of the sea" – given to this herb due to its resemblance to the water against the sea cliffs in its native Mediterranean homeland. It is a plant rife with history, having been used throughout the ages as a memory-booster, as well as a sign of love and prosperity. It was particularly symbolic at weddings, even worn as a head wreath by Anne of Cleves and given as prettily wrapped up branches to the wedding guests.
Probably most well-known as a cooking herb worldwide, Rosemary is not only a beautiful bonsai subject but a functional one as well. These semi-woody perennials may grow to a height of 4-5 feet in their natural habitat, and are available in about 24 different cultivars, with bloom colors ranging from pink, to white, blue, and violet.
Its resemblance to pine (right down to the scent of most varieties) makes this shrub a draw for enthusiasts. The blue-gray foliage is made up of short, narrow leaves (averaging just an inch long) that strongly mimic the look of pine needles. The flowers are small and vibrant and may bloom in spring, late fall, or even winter. The exfoliating bark is furrowed and rough, giving way to a lighter, smoother surface beneath.
This herbal bonsai is very hardy and can remain outdoors until temperatures drop below 30° F. It loves warmth and humidity, and should be provided with at least 6-8 hours of sunlight per day so be sure to place it near a south-facing window or door wall when kept inside. Once the frost danger has passed, move your Rosemary back outdoors. Using a humidity tray during the months that your plant spends indoors will help keep the foliage from drying out.
Rosemary is sensitive to drought so should not stay dry for extended periods of time, however they do prefer to be a bit on the drier side overall. A terra cotta clay pot is the perfect container for this species because it allows the soil to dry out more quickly. Because it is also sensitive to overwatering, there must be a balance of good drainage and sufficient moisture levels.
Apply a non-acid liquid fertilizer – 20-20-20 works well – every two weeks during the growing season. Over the winter, particularly if the plant is indoors, feeding may be reduced to once a month. Alternatively you can use a time-release formula, administered according to the instructions.
Styles – cascade, semi-cascade, windswept; some cultivars work well as uprights while others grow more prostrate, so customize the style to the variety of plant that you have.
Rosmarinus officinalis is an herb, so naturally responds well to trimming. Begin pruning after the flowers have stopped blooming and do not remove more than one third of the plant. You can form cushions of the branches by continually reducing the new shoots. One of the most exciting things about this bonsai is that you can wrap the pruned sprigs together in a bundle and hang dry them in a cool place – you will then have a usable culinary item from your bonsai.
Wiring may be done on branches that are half the diameter of a pencil. This needs to be done with caution as the branches are easy to snap. Clip and grow is generally a sufficient training method for this plant.
This is most easily carried out via cuttings. Semi-hardwood or softwood cuttings may be taken in summer. Cut a length about two inches and remove the leaves. Place in a mixture of peat moss and perlite, keeping moist until they set roots, then transplant as you would a normal bonsai.
R. Officinalis should be repotted about once a year. Spring is the ideal time but it can be done any time of year. If you want to maintain your plant at the same size, prune the roots down a couple of inches on the bottom and sides of the root mass and replace into the same pot with a well-draining bonsai soil. Trim some of the foliage at the same time so that the roots don't become overworked and stressed.
Insects/Pests & Diseases
This aromatic is remarkably resistant to pests. It can, however, be vulnerable to root rot, particularly if not allowed to dry out a bit between watering. Watch for browning or blackening of tips of the leaves. This can be a sign of roots that are drowning or have developed a fungal case of root rot. If you notice these signs, hold off on watering until the soil has dried out – a good way to tell is to use a moisture meter for a quick and accurate moisture reading at the root level.
If meter reads low moisture or dry, go ahead and give your Rosemary bonsai a thorough watering, then repeat the cycle of waiting until it dries out before watering again.