Roselle (Tea Hibiscus)

Sow seed into flats in a greenhouse or under lights and keep them warm; germination takes five to 10 days depending on type and temperature. Grow the seedlings on for four to six weeks, then transplant to the field once frost danger has passed. Roselle will not flower until the days shorten in late summer, so the calyx crop always ripens late; the weeks you gain indoors are the weeks that let the calyces fill before frost ends the season.

Set plants about 36 inches between rows and 18 inches apart within the row, in full sun on well-drained soil. Wait until frost danger has passed - roselle is frost-tender and cold checks it hard. Roselle builds a tall, wide frame before it ever flowers, and crowding costs you the side branches that carry the calyx crop.

Two to four weeks after planting, apply fertilizer based on the results of your soil test rather than a standard rate. Roselle spends three to four months building its frame before it ever flowers, and matching fertility to the deficit your soil actually has is what supports that frame without wasting inputs.

While the plants are still young and well before the short days of late summer arrive, pinch out the growing tips. Each pinch pushes out new lateral shoots. Flowers, and therefore calyces, form on flowering shoots - early pruning increases branching and the development of more flowering shoots, so the more branches the plant carries into the short-day window, the bigger the harvest.

Walk the planting regularly and check the leaves for chewing insects. Remove and dispose of affected leaves or plants physically as soon as you see damage, and note any unusual symptoms early. Roselle is generally tolerant of insect attack and disease problems are rare in it, so hand removal usually ends the problem before it ever justifies anything stronger.

Watch the bloom fade and fall, then come back about two weeks later when the calyx behind it has reached full size. Snap it off while it is still plump, tender and glossy, and twist the seed pod out of the middle. Pick early and often to keep new calyces coming. The calyces are fleshy and ready for harvest when they reach their maximum size two weeks after flowering; left past that they go brown and leathery on the plant, which is tough and no good for tea.

After the last calyces come off, pull the plants and look the roots over for the knots and swellings of root-knot nematode. If you find them, plant roselle somewhere else next year. Root-knot nematodes are roselle's major pest, and they build in the soil wherever a susceptible crop repeats - crop rotation is the practical control, and the roots at pull-out are the only honest look you get at the population.

Plan the calyx harvest to finish before temperatures drop below 40F. If an early cold snap threatens while calyces are still filling, cover the plants overnight to buy a few more ripening days. Roselle is hardy only in zones 9 and 10 and is damaged by frosts or freezes, and because bloom is triggered by shortening days the crop ripens right into the cold end of the season.