A Comprehensive Guide on Growing Rosella

What rosella is, and what you harvest

Hibiscus sabdariffa, known here as rosella, is grown for its fleshy red calyces: the cup of sepals that swells around the seed pod once the flower drops. The calyces, not the petals, are what goes into jam, cordial, sauce and tea. The young leaves are edible too, sharp and lemony in stir fries and salads.

Climate and timing

Rosella is a warm season annual and it is frost sensitive: a light frost checks it and a real one kills it. It also needs a long season, roughly five to six months from sowing to the first calyces, so the job is to get it in early enough to finish before the cold. Plants reach about 1.5 to 2m and spread almost as wide, and they need full sun, because rosella will not crop in shade or half shade.

Rosella also flowers in response to shortening days rather than to its own age. Flowering therefore begins in mid to late summer or autumn however early you sowed. Sowing early does not bring it forward, it gives the plant time to build a bigger frame, and a bigger plant carries far more calyces. In south east Queensland, plants usually start flowering in Jan or Feb and are picked from Mar to May.

When to sow, zone by zone

• Tropical (the Top End, far north Queensland and the Kimberley): sow Aug to Mar, the easiest zone for rosella by a long way.
• Subtropical (south east Queensland up to Bundaberg and the NSW north coast): sow Sep to Jan, with Sep and Oct the best months.
• Temperate (coastal NSW and southern Victoria, including Sydney and Melbourne): sow in Nov once frost has passed, starting seed in pots a few weeks earlier. Expect a modest crop.
• Mediterranean (Perth, Adelaide, the south west of WA and the SA gulf country): follow the temperate month of Nov, and carry the plant through the dry summer with deep watering and a thick mulch.
• Arid and semi-arid (inland NSW, SA, WA, the NT and western Queensland): the sowing calendar does not list rosella inland, where the frost free window is short at both ends. Where autumn frosts come late, an Oct sowing in the warmest corner is worth a trial.
• Cool and alpine (Tasmania, Canberra, and the tablelands and alpine districts of NSW and Victoria): too short a season for a reliable crop. Grow it in a large pot in the warmest spot and treat any calyces as a bonus.

These are broad groupings, and gardeners between zones should lean on their own first and last frost dates, because with rosella the frost date is the whole story.

Soil, sowing and water

Rosella grows best in a well drained soil with plenty of organic matter, so dig compost or aged manure through the bed a few weeks before sowing.

Soak the seeds in water for 30 minutes to an hour to soften the hard seed coat, then sow about 1cm deep and cover them with soil. Where conditions are rough, raise seedlings in trays and transplant once they have four true leaves. Keep the seedbed moist but not wet, since overwatering kills seedlings faster than anything else. Space plants 1 to 1.5m apart, because crowded bushes give small calyces, and mulch to hold moisture. Once the plants are away, water deeply and less often, checking the soil with a finger rather than working to a schedule.

Pests, disease and rotation

Rosella is tough but not trouble free. Root knot nematode is the serious one: common in warm sandy soils in the north, it stunts plants and galls the roots, and rosella is susceptible. Rotate the bed each year, avoid following other susceptible crops such as tomatoes, and keep adding organic matter, which supports the soil life that holds nematode numbers down. Our guide to root-knot nematode shows what to look for. Leaf eating beetles and grasshoppers chew the foliage in summer, and hand picking usually keeps up.

Picking leaves and harvesting calyces

Once the plant has branched well, pick some of the younger leaves for the kitchen, since light picking encourages the bushy growth that carries the crop. Stop once flower buds appear and let the plant put everything into the calyces.

Each flower lasts about a day, drops, and the calyx behind it swells and colours deep red. Pick when the calyx is about 20 to 25mm across and still crisp, because older ones turn woody. Cut them with sharp scissors or secateurs rather than pulling, and go over the plant every few days, since regular picking keeps new calyces coming. To use them, cut around the calyx and slip the green seed pod out.

Saving seed, and keeping rosella where you put it

Leave a few calyces on the bush to mature rather than picking them all. Once the pods are brown and brittle, split them, shake the seed out, dry it for a few more days and store it in a paper envelope somewhere cool and dark. Saved seed stays viable for several years, and fresh rosella seed is there if you would rather start again.

Rosella has naturalised in parts of northern Australia and is rated a moderate priority environmental weed in Western Australia, so in the north it pays to keep track of where the seed ends up. Deadhead any calyces you are not saving before the pods dry and split, bin or hot compost spent plants rather than piling them at the fence line, and keep it away from gardens backing onto bushland, creeks and wetlands. In cooler districts, where frost kills the plant every year, it does not persist.

Related growing guides

• Rosella: From a Spring Seed to a Jar of Crimson Jam
• Root-Knot Nematode: The Hidden Cause of Wilting and Forked Roots
• Growing Vegetables in the Subtropics and Tropics: What Works

Ready to plant? Browse our Rosella seeds.