Ornamental · Geraniaceae
Rozanne Cranesbill
Geranium 'Rozanne'
A low mound of green topped with violet-blue, white-centered flowers from late spring to fall.
Full sun
Every 5–10 days
USDA 5–8
12–18 in · 30–46 cm
Overview
Hardy geranium 'Rozanne' grows as a low, spreading mound of green foliage that hugs the ground. It is a true cranesbill, and the name points to a physical detail: the slim, beak-shaped seed pods that form where the flowers fade, like a crane's bill in miniature. It should not be mistaken for the tender scented Pelargonium that carries the same everyday name, since this is a cold-hardy perennial that regrows across zones 5 to 8.
The flowers are the plant's signature. Held just above the leaves from late spring into fall, they open a saturated violet-blue with a pale white eye at the center, appearing in a near-constant succession across the mound. That long, steady flush of color is what earned it Perennial Plant of the Year in 2008.
Up close, the plant reads as a dense, ground-covering cushion of stems and leaves that spreads sideways and knits over bare soil. It holds its color through summer heat better than most cranesbills and is passed over by deer and rabbits. Given sun, drainage, and a midseason cutback, it keeps up months of violet-blue bloom for very little work.
Care
The short version: plant it in full sun to part shade in average, well-drained soil, water it through dry spells, and shear the whole mound back after the first flush to bring the violet-blue flowers back into fall.
Light
The violet-blue flowers come thickest in full sun, though the plant also holds up in partial shade and partial sun. In hot regions a little afternoon shade helps, since it eases the heat stress that can leave the mound looking flat by midsummer.
Water
Give it average, medium moisture and let the top inch or so of soil dry between waterings, which works out to roughly every 5 to 10 days. Established plants take some drought, but the foliage looks fullest when it is not left parched, so water through dry spells to keep the flowers coming.
Soil
The roots take to loam, clay, or sand as long as the ground drains well. The plant grows lushest in moist, organic-rich soil, so a little worked-in compost pays off in denser foliage. No particular pH is needed.
Temperature
This cold-hardy perennial comes through winters down to -20°F (-29°C) and summer heat up to about 90°F (32°C). That wide range is what keeps the green mound returning across zones 5 to 8 without special protection.
Humidity
Ordinary outdoor humidity suits it, so there is no level to manage. Airflow matters more than humidity, since still, damp air trapped among crowded leaves is what marks them with leaf spot and rust.
Feeding
It feeds lightly. Work compost or organic matter into the soil as the growing season opens, or give a balanced general-purpose feed in spring, and that keeps the foliage green and the flowers coming. There is no need to feed all summer.
Pruning
This is the one job that pays off. Once the first flush of violet-blue flowers fades, cut the whole mound back hard to renew the foliage and draw out a fresh late-summer or early-fall rebloom. Wayward side stems can be trimmed any time to keep the spread neat.
Repotting
In the ground the plant rarely needs lifting and divides on its own schedule. In a container, repot when you see roots circling the pot, the flowering thin out, or the soil drying out unusually fast.
Size & spacing
The mound stays low, about 12 to 18 inches (30 to 46 cm) tall, and fans out 12 to 24 inches (30 to 61 cm) wide. Setting plants toward the wider end of that range lets air move through the leaves and keeps the foliage clean.
When to plant
'Rozanne' is a hardy perennial, so the season is about settling the plant in rather than beating the frost. Set new plants out in spring once the last frost has passed, or in early fall while the soil still holds warmth, and the violet-blue flowers open from late spring through to early autumn.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Plant: Spring after the last frost, or early fall
- Harvest: Late spring (May) through summer to early fall, often nearly continuous
Hardiness
USDA hardiness zones: 5–8
Temperature: down to -29°C
Troubleshooting
'Rozanne' is famously trouble-free, and most of what does appear shows up as marks on the green leaves in wet, crowded conditions. Learn the few signs below and you can step in early, while the fix is still simple. Good airflow and watering low at the base head off nearly all of it.
The mound going limp and sinking to the ground
When the whole low mound goes slack and sinks in hot weather while the soil underneath stays wet, the cause is likely southern bacterial wilt, a disease that thrives in warm, waterlogged ground and offers no cure. Lift the collapsed plant, destroy it, and keep susceptible perennials out of that soil. In hot regions, a spot with afternoon shade and quick-draining ground keeps the stems firm and upright and out of the danger zone.
Fix:
- Remove and destroy affected plants
- Avoid replanting susceptible species in the same soil
- Reduce afternoon heat stress by providing some afternoon shade in hot climates
Brown or tan spots freckling the green leaves
Those discrete brown-to-tan flecks scattered over the leaf blades are fungal leaf spot, which takes hold after wet weather or overhead watering leaves the foliage sitting damp. Pick off the freckled leaves, thin the clump so air threads through it, and water low at the base. The blemishes stay on the surface, and fresh green growth pushes back in once the leaves dry.
Fix:
- Remove and discard affected leaves
- Improve air circulation by thinning or spacing plants
- Water at the base rather than overhead
Raised orange dots crusting the leaf undersides
Tip a leaf toward the light and the raised orange-to-brown dots crusted along the underside are the spore pustules of rust fungus, which multiplies through crowded, damp leaves. Strip off the crusted leaves and destroy them, spread the clump so air moves between the stems, and keep water off the blades. The pustules never break past the leaf surface, so the violet-blue flowers keep opening above them.
Fix:
- Remove and destroy infected foliage
- Increase spacing and air circulation
- Avoid overhead irrigation
Toxicity
Good news for pet owners: true hardy geranium is safe. Neither the leaves nor the violet-blue flowers carry a toxin dangerous to cats, dogs, horses, or other animals, and they hold no poison rating for people either. The only plant to watch for is the unrelated scented Pelargonium, sometimes sold under the same common name.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
A cat that bites into one of the soft green leaves or a violet-blue petal is in no danger, since true hardy geranium carries no toxin. Only a very large mouthful of any plant might leave any animal briefly queasy.
Dogs None
A dog that crunches a slender stem or a white-centered bloom finds nothing poisonous in it. With no toxin present, the worst outcome is the mild tummy grumble that any leaf or flower can bring.
Horses None
Horses can crop the green foliage around it with no harm done, because the plant holds no compounds dangerous to them. The aromatic leaves tend to keep grazers moving on regardless.
Rabbits None
A rabbit that nips at the deeply cut leaves takes no toxic dose, and in fact rabbits usually pass this foliage by. That makes it a sound pick where they browse.
Livestock None
Cattle, goats, and sheep that graze the low green mound are in no danger from true geranium, which holds nothing that troubles farm animals. A chewed clump is a loss of leaves and flowers, not a health risk.
Birds None
Birds that peck at the leaves or the violet-blue flowers are perfectly safe, since neither part holds a toxin. A pecked petal does no harm.
People None
For people, children included, the leaves and flowers carry no poison rating at all. Rinsing your hands after touching any plant is a fair habit, but nothing on this one poses a specific hazard.
Wash hands after handling as a general gardening practice; no specific toxicity hazard is reported for true Geranium.
Varieties
'Rozanne' is the standout, but a couple of close relatives are worth knowing if you want a paler blue or a different flower color entirely.
Geranium 'Rozanne' (syn. 'Gerwat')
This is the patented sterile hybrid itself, a low clump-former whose violet-blue, white-centered flowers open from late spring to fall and hold their color through summer heat, the very display that won it Perennial Plant of the Year in 2008.
Geranium 'Azure Rush'
A sport of 'Rozanne' that blooms just as long but in a paler, lighter blue, its flowers set over a neater, more compact mound of foliage.
Geranium sanguineum (Bloody Cranesbill)
A true cranesbill species rather than a hybrid, marked out by its bright magenta-pink flowers and often placed beside 'Rozanne' where the two colors can be seen together.
Companions
'Rozanne' shines as a long-blooming groundcover at the feet of taller plants, weaving between shrubs and upright perennials that enjoy the same sun and average moisture.
Plant near
Roses: Mounding hardy geranium foliage covers bare lower rose stems and provides a long-blooming groundcover at the base.
Ornamental grasses: Contrasting upright form pairs well with the sprawling mound and extends seasonal interest in borders.
Daylilies and other clumping perennials: Similar culture (full sun to part shade, average moisture) and complementary bloom times in mixed borders.
How to propagate
Because 'Rozanne' is a sterile hybrid, you cannot raise it from seed. Every new plant comes from dividing an existing clump or rooting a cutting, both of which reproduce the same violet-blue, white-centered flowers exactly.
DivisionEasy
Spring or early fall · One growing season
Division is the most reliable way to multiply this sterile hybrid. Lift a mature clump in spring or early fall, tease the crown and roots into pieces that each hold a share of healthy roots, and set them back in the soil at once. Each rooted piece knits into a full green mound over a single growing season.
Stem cuttingsModerate
Spring to early summer · Several weeks to a few months to root and establish
Basal or softwood cuttings taken from spring through early summer offer a slower second route, calling for more patience than dividing the clump. The cut stems take several weeks to a few months to send out roots and establish. Seed is never an option, since the plant is sterile.
Myths
Hardy geranium 'Rozanne' is toxic to cats and dogs.
The mix-up sits in a shared name. The plant the ASPCA lists as toxic 'Geranium' is really Pelargonium, the tender scented bedding plant of a separate genus. True hardy Geranium, the cranesbill, including 'Rozanne', is not listed as toxic to pets, so its leaves and violet-blue flowers are safe to grow around them.
You can grow more 'Rozanne' from its own seeds.
'Rozanne' is a sterile hybrid that sets little or no viable seed, and any seed it drops will not grow up matching the parent's violet-blue, white-centered flowers. Vegetative propagation is the only reliable route, whether by dividing a clump or rooting basal cuttings.