Rosemary for Bonsai

by Matthew Ward

Introduction

This information was compiled thru numerous Internet postings to the bonsai mail list and rec.arts.bonsai. For addition info, see Bender's "Herbal Bonsai", Lesniewicz's "Bonsai in Your Home", and Bonsai Today #53 (Jan-Feb 1998). The format was inspired by Sabrina Caine's "Tree of the Week" project.

Rosemary, Arp Rosmarinus officinalis

Rosemary is a long-lived, semi-woody, tender perennial herb that can become a bonsai in a single year with a minimum of effort. Rosemary can reach a maximum height of 48" if field grown in only three years and live as a bonsai for over 30 years. Since the Rosemary's leaves are needle-like, the plant is most often grown in the same classic bonsai styles as the pine.

Rosemary has been long cultivated as an herb and ornamental. The herb now is available in an astounding number of cultivars (24!) with an abundance of flower colors (Blue, Violet, Pink, White), scents (Pine, lemon), and growth habits (upright, twisting, creeping). There's even a variegated cultivar. With some cultivar hardy to zone 7, Rosemary can be grown out-of-doors all year round. In colder climes, the herb can successfully be overwintered indoors under lights.

Lighting and Temperature

Full Sun in all zones, a minimum of 6 hours of direct sunlight per day during spring/summer/autumn. When overwintering indoors, give it 14 hours under full-spectrum lamps or a sunny spot with direct morning sun.

Rosemary is a tender perennial in zones 11-7 and an annual in zones 6-3. For a bonsai, bring indoors before first frost date. A single light frost is unlikely to kill any cultivar of rosemary. A properly hardened off Rosemary (of the hardier cultivar) can withstand brief 20F temperatures if field planted. During indoor wintering, give it cool days (~70F) and cooler nights (65-60F)with lots of morning sun, no afternoon sun, and lots of air circulation.

Water and Fertilizer

Rosemary does not like wet feet. It can survive dry soil for a day or two. Best to let the soil dry out almost completely then water. Use a chopstick to determine soil moisture. When the chopstick is pulled out and feels totally dry (cannot smear mud on dry paper), then water. Only water in the morning to prevent the roots from sitting in water overnight.

Humidity should be maintained at over 50% (relative) with the use of a humidifier or humidity tray.

Use 20:20:20 non-acidic liquid fertilizer every other week as long as day temperatures are above 50F. While wintering indoors, reduce feeding to once monthly. Watch for nitrogen deficiency, especially with the organic mix given below. Time released Oscomote (36:18:12) also has proven to work well. There is no need to dilute fertilizer past the manufacturers recommendation.

Repotting

Repot every other year in very well drained mix of 50% organics such as screened fir or pine bark and 50% inorganics (pumice, perlite, haydite, etc). Add limestone or dolomite to the soil mix to buffer the pH of the soil mix. Do not use peat moss.

Try to limit any root pruning to the early spring, before the new growth gets too advanced. Never root prune by more than 1/3 during any year.

Styling

Rosemary comes in both upright and prostrate varieties. Rosmarinus officinalis forms itself into a striking formal upright with minimum effort. The prostrate varieties can be formed into everything from informal upright cascade to windswept. The only style that the species does not lend itself to is root over rock.

Clip and grow is the best styling method since the wood, once hardened, is impossible to bend without splintering. You can pinch new growth after the first sets of leaves completely open. Start midsummer by cutting back top foliage to old wood to encourage some of the lower and finer branches to expand and thicken.

Propagation, Pest and Diseases

Usually grown from softwood and semi-hardwood cuttings in summer using low IBA rooting hormone. Rootone TM, or Hormex #1 or #3 TM or Dip and Grow TM at 20:1 dilution are sufficient. Cuttings are placed in sterile media and root in 2-4 weeks.

Rosemary is subject to root rot in poorly draining soils or when grown in inadequate light.

Cultivars Suitable for Bonsai

Rosemary, Arp, (Rosmarinus officinalis)
Zones: 7-10 (very hardy H1)
Flowers: pale blue, summer
Growth Habit: upright
Other: green-gray foliage
Uses: ornamental and culinary, popular bonsai subject

Rosemary, Benenden Blue (Rosmarinus officinalis 'Benenden Blue')
Zones: 8-10
Flowers: blue, midsummer
Growth Habit: upright
Other: dark green foliage, bred for deep blue flowers
Uses: ornamental and culinary

Rosemary, Blue Lady (Rosmarinus officinalis 'Blue Lady')
Zones: 8-10
Flowers: blue-violet, summer
Growth Habit: twisted
Other: very narrow leaves, very needle-like. (Popular Bonsai subject)
Uses: ornamental and culinary

Rosemary, Blue Spires (Rosmarinus officinalis 'Blue Spires')
Zones: 8-10
Flowers: Bright blue flowers on tall upright stems
Growth Habit: creeper
Other: specially developed for visual and olfactory appeal.
Uses: *very* ornamental and yet still culinary

Rosemary, Collingwood Ingram (Rosmarinus officinalis 'Collingwood Ingram')
Zones: 8-10
Flowers: blue, summer
Growth Habit: creeper
Other: highly fragrant, bright green foliage
Uses: ornamental and culinary

Rosemary, Foresteri (Rosmarinus officinalis 'Foresteri')
Zones: 8-10
Flowers: blue, summer
Growth Habit: upright
Other: especially drought resistant
Uses: ornamental and culinary

Rosemary, Girardus (Rosmarinus officinalis 'Girardus')
Zones: 8-10
Flowers: blue, summer
Growth Habit: upright
Other: very, very dense foliage
Uses: culinary (Very rare in U.S. of A.)

Rosemary, Golden Rain (Rosmarinus officinalis 'Joyce de Baggio')
Zones: 8-10
Flowers: blue, summer
Growth Habit: upright
Other: variegated (yellow on foliage edges) increasing variegation with age.
Uses: ornamental and culinary

Rosemary, Gorizia (Rosmarinus officinalis 'Gorizia')
Zones: 8-10
Flowers: blue, summer
Growth Habit: upright (larger then most)
Other: densely packed branches of dark green needles, fragrant
Uses: ornamental and culinary

Rosemary, Hill Hardy (Rosmarinus officinalis 'Hill Hardy')
Zones: 7-10 (very hardy Gloxinia)
Flowers: blue, summer
Growth Habit: upright
Other: needlelike foliage, fragrant
Uses: ornamental and culinary

Rosemary, Kenneth's Prostrate (Rosmarinus officinalis 'Kenneth's Prostrate')
Zones: 8-10
Flowers: blue, late summer and early fall
Growth Habit: creeper
Other: fast grower
Uses: ornamental and culinary

Rosemary, Lockwood de Forest (Rosmarinus officinalis var. angustifolius 'Lockwood de Forest')
Zones: 8-10
Flowers: lavender blue, summer
Growth Habit: creeper
Other: dark green foliage
Uses: ornamental and culinary

Rosemary, Logee's Blue (Rosmarinus officinalis 'Logee's Blue')
Zones: 8-10
Flowers: Blue, summer
Growth Habit: upright
Other: bluish green foliage, smaller Ogee's.
Uses: ornamental and culinary

Rosemary, Miss Jessup (Rosmarinus officinalis 'Miss Jessup')
Zones: 8-10
Flowers: Blue
Growth Habit: upright
Other: bred especially for flowering
Uses: ornamental and culinary

Rosemary, Mrs. Howard's Creeping (Rosmarinus officinalis'Mrs. Howard's Creeping')
Zones: 8-10
Flowers: small blue, mid to late summer
Growth Habit: creeper
Other: fast grower
Uses: ornamental and culinary

Rosemary, Pine-Scented (Rosmarinus officinalis 'Pine-Scented')
Zones: 8-10
Flowers: Blue, summer
Growth Habit: upright, feathery needle-leaves
Other: grown as miniature Christmas Tree, leaves have pine fragrance.
Uses: ornamental and culinary

Rosemary, Rex (Rosmarinus officinalis 'Rex')
Zones: 8-10
Flowers: Blue, summer
Growth Habit: upright
Other: dark green foliage
Uses: ornamental and culinary

Rosemary, Santa Barbara (Rosmarinus officinalis 'Santa Barbara')
Zones: 8-10
Flowers: Blue, summer
Growth Habit: upright
Other: drought resistant
Uses: ornamental and culinary

Rosemary, Severn Sea (Rosmarinus officinalis 'Severn Sea')
Zones: 8-10
Flowers: Violet-blue
Growth Habit: upright
Other: ornamental and culinary

Rosemary, Spanish (Rosmarinus officinalis 'Majorca')
Zones: 8-10
Flowers: Pink, throughout summer.
Growth Habit: upright
Other: very needlelike leaves (popular bonsai subject)
Uses: ornamental and culinary

Rosemary, Tuscan Blue (Rosmarinus officinalis 'Tuscan Blue')
Zones: 8-10
Flowers: Blue, mid spring to late summer
Growth Habit: upright
Other: extremely fragrant, bred especially for dense flowering.
Uses: ornamental and culinary

Rosemary, White-Flowered (Rosmarinus officinalis 'White-Flowered')
Zones: 8-10
Flowers: White
Growth Habit: upright
Other: extremely fragrant
Uses: ornamental and culinary

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