Ornamental · Geraniaceae
Rozanne Cranesbill
Geranium 'Rozanne'
One of the longest-blooming perennials you can plant, and it asks for almost nothing in return.
Full sun
Every 5–10 days
USDA 5–8
12–18 in · 30–46 cm
Overview
Hardy geranium 'Rozanne' is the workhorse of the sunny border. It belongs to the true cranesbill clan, named for the slim beak-shaped seed pods that follow the flowers, and it should never be confused with the tender scented Pelargonium that shares the everyday name geranium. This is a cold-hardy perennial that comes back year after year through zones 5 to 8.
What sets it apart is the bloom. From late spring right through to fall it carries violet-blue flowers with pale white centers, often without a real pause, on a low spreading mound that knits through a planting and covers bare ground. It earned Perennial Plant of the Year in 2008 on the strength of that performance and its easygoing nature.
It also handles heat better than most cranesbills, and it tends to be left alone by deer and rabbits. Give it sun, soil that drains, and a midseason haircut, and 'Rozanne' rewards you with months of color 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 it back after the first flush to keep the flowers coming into fall.
Light
'Rozanne' flowers best in full sun, but it takes partial shade and partial sun in stride. In hot regions a little afternoon shade actually helps, easing the heat stress that can make the plant flag in midsummer.
Water
Give it average, medium moisture and let the top inch or so of soil dry between drinks, which works out to roughly every 5 to 10 days. Established plants take some drought, but don't leave them parched, and water during dry spells to keep the bloom going.
Soil
It isn't fussy and grows in loam, clay, or sand as long as the ground drains well. It does its best in moist, organic-rich soil, so work in some compost where you can. There's no particular pH it needs.
Temperature
This is a cold-hardy perennial that handles winters down to -20°F (-29°C) and summer heat up to about 90°F (32°C). That range is what lets it thrive across zones 5 to 8 with no special protection.
Humidity
Ordinary outdoor humidity suits it, so there's no number to manage. Airflow matters more than humidity here, since still, damp air around crowded foliage is what invites leaf spot and rust.
Feeding
It feeds lightly. Work some compost or organic matter into the soil at the start of the growing season, or give a balanced general-purpose feed in spring, and that carries it through. There's no need to keep feeding all summer.
Pruning
This is the one job that pays off. After the first flush fades, cut the whole plant back hard to tidy it and trigger a fresh late-summer or early-fall rebloom. You can trim wayward side stems any time to keep the spread in check.
Repotting
Plants in the ground rarely need lifting and divide on their own schedule. In a container, repot when you see roots circling the pot, flowering tail off, or the soil drying out unusually fast.
Size & spacing
Expect a low mound around 12 to 18 inches (30 to 46 cm) tall that spreads 12 to 24 inches (30 to 61 cm) wide. Space plants toward the wider end of that range so air moves freely and the foliage stays clean.
When to plant
'Rozanne' is a hardy perennial, so the season is about getting it established rather than racing the frost. Set new plants out in spring once the last frost has passed, or in early fall while the soil is still warm, and the flowers run 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 turn up shows on the 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 base watering head off nearly all of it.
The whole plant wilts and collapses even in moist soil
When a clump flops in hot weather despite plenty of water, suspect southern bacterial wilt, which thrives in warm, soggy ground and has no cure. Dig the plant up, destroy it, and don't replant a susceptible perennial in that spot. In hot regions a little afternoon shade and soil that drains freely keep the plant 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 scattered across the leaves
This is fungal leaf spot, and it shows up after spells of wet weather or overhead watering keep the foliage damp. Pull off the marked leaves, thin or space the clump so air moves through it, and water at the base from now on. It rarely does lasting harm and the plant shrugs it off once things dry out.
Fix:
- Remove and discard affected leaves
- Improve air circulation by thinning or spacing plants
- Water at the base rather than overhead
Rusty orange bumps on the undersides of the leaves
Flip a leaf over and you will find the raised spore pustules of rust fungus, which spreads fastest on crowded, damp foliage. Strip off the infected leaves and bin them, open the planting up for better airflow, and keep the water off the leaves. The damage is cosmetic, so the clump keeps blooming through it.
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. The cranesbills carry no toxin dangerous to cats, dogs, horses, or other animals, and they hold no poison rating for people either. The only plant to watch out for is the unrelated scented Pelargonium, which is sometimes sold under the same common name.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
True hardy geranium is safe for cats. A cat that nibbles a leaf or flower won't be poisoned, though a big mouthful of any plant can leave any animal with a passing upset stomach.
Dogs None
Dogs are fine around cranesbill. There's no toxin to worry about, so a curious dog that chews a stem or bloom faces nothing worse than the mild tummy grumble any plant material can cause.
Horses None
Horses can graze near this plant without harm. It carries no compounds dangerous to them, and grazing animals tend to leave the aromatic foliage alone anyway.
Rabbits None
Rabbits won't be poisoned by it, and in fact this is one of the plants rabbits tend to skip. That makes it a sensible choice for a garden where they roam.
Livestock None
Cattle, goats, and sheep are in no danger from true geranium. The plant holds nothing that troubles farm animals, so a grazed clump is a gardening loss rather than a health risk.
Birds None
Backyard and pet birds are safe around it. There's no toxin in the leaves or flowers, so a peck or two does no harm.
People None
True cranesbill carries no poison rating for people, including children. Wash your hands after handling any plant out of habit, but there's no specific hazard here.
Wash hands after handling as a general gardening practice; no specific toxicity hazard is reported for true Geranium.
Varieties
'Rozanne' is the star, but a couple of close relatives are worth knowing if you want a lighter shade or a different flower color.
Geranium 'Rozanne' (syn. 'Gerwat')
This is the patented sterile hybrid itself, a clump-former that pumps out violet-blue, white-centered flowers from late spring to fall and shrugs off summer heat, which earned it Perennial Plant of the Year in 2008.
Geranium 'Azure Rush'
A sport of 'Rozanne' that keeps the same long bloom but carries paler, lighter blue flowers on a tidier, more compact mound.
Geranium sanguineum (Bloody Cranesbill)
A true cranesbill species rather than a hybrid, grown for its bright magenta-pink flowers and often set beside 'Rozanne' as a point of comparison.
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 can't grow it from seed. Every new plant comes from dividing an existing clump or rooting a cutting, both of which copy the parent 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, split it into pieces with healthy roots, and replant them straight away. Each division settles in and fills out over a single growing season.
Stem cuttingsModerate
Spring to early summer · Several weeks to a few months to root and establish
You can also root basal or softwood cuttings taken from spring through early summer, though it asks for more patience than division. Expect them to take several weeks to a few months to root and establish. Seed is never the route here, since the plant is sterile.
Myths
Hardy geranium 'Rozanne' is toxic to cats and dogs.
The confusion comes from a name. The plant on the ASPCA toxic list called 'Geranium' is really Pelargonium, the tender scented bedding plant, which belongs to a separate genus. True hardy Geranium, the cranesbill, including 'Rozanne', is not listed as toxic to pets and is safe to grow around them.
You can grow more 'Rozanne' plants from its seeds.
'Rozanne' is a sterile hybrid that sets little or no viable seed, and what seed it does drop won't come true to the parent. The only reliable way to get more is to propagate it vegetatively, by dividing a clump or rooting basal cuttings.