Tall and dramatic, ‘Roi Humbert’ combines bold scarlet flowers with bronze foliage. A “sensation” in 1915 (Livingston Seed catalog), ‘Roi’ later played a leading role in the Red Borders at Hidcote, and chances are your grandparents grew it — or still do! Aka ‘Red King Humbert’, though some experts disagree. From Oklahoma. Last offered in spring 2007. Learn more. Widely available elsewhere.
SUB TYPE bronze leaves, American
SOURCE Oklahoma, America
LIGHT full sun
PLANTING & CARE
Like most cannas, ‘Ehemanii’ is easy to grow. All it needs is plenty of sunshine, heat, and water. Unfortunately, unlike most cannas, it doesn’t store well as a dormant rhizome, which is one reason it’s rarely offered today — and why we ship freshly-dug rhizomes in April. Please give yours immediate attention when it arrives or you may lose it.
The weather in April isn’t warm enought to plant ‘Ehemanii’ outside in most places, so you’ll probably need to start it INDOORS in a pot. A clay pot is ideal. Choose one that’s a bit snug because excess empty soil can sour and lead to rot. Plant a couple of inches deep — look for where the stalk changes from green to white due to being underground.
Put the pot in a WARM spot with as much sun as possible. Bottom heat is helpful, and although a plastic heat mat is the safest way to provide this, many gardeners improvise. Keep soil damp but not soggy until new growth appears. Repot as needed, and don’t plant outside till all danger of frost is past, the soil has warmed up, and nightly lows are reliably above 55° F.
Outside, plant in full sun, 24-36” apart. (‘Ehemanii’ gets big!) Well-drained, fertile soil is ideal, but ‘Ehemanii’ is vigorous and adaptable. Growing it in a large pot — on a sunny terrace or deck, for example — can also work well.
Like all cannas, ‘Ehemanii’ is a very thirsty plant (once it gets going again). It will thrive, grow taller, and bloom more when watered regularly. In fact, when it’s in active growth it’s hard to water it too much. Thoroughly soak the area at the base of the stalks, where the rhizomes are multiplying. A sprinkling system or sprinkler will rarely provide enough water.
Fertilizing is a big help, too, because all cannas are heavy feeders. Give it some rose or tomato fertilizer (not too high in nitrogen) every 2-4 weeks, or use a foliar fertilizer (Miracle-Gro, etc.). Compost is a great help, too.
Pluck off spent flowers to enhance its beauty. To encourage more bloom, cut off flower clusters before seed-pods form.
In some areas, canna leaf-roller caterpillars can be a problem for any canna. If necessary, control with Bt or insecticide. Learn more at entomology.ifas.ufl.edu/creatures/orn/brazilian_skipper.htm.
WINTER CARE — In zones 7 and colder, if you want to save your ‘Ehemanii’ for the following year you’ll need to dig it in the fall and either (a) store it as dormant rhizomes or (b) keep it growing indoors all winter.
To store as dormant rhizomes, wait a week or so after the foliage is “blackened” by frost, to allow the rhizomes to harden and fully mature. The soil will generally protect them from freezing. Then cut the stalks off a few inches above ground level. You’ll find that the original rhizome you planted has increased into a much larger clump, so be careful when digging it up — start a foot or so away from the stalks. Wash off all soil, cut the stalks down as short as possible, and allow it to dry thoroughly in a cool, dry place for a couple of days. If necessary you can break it into smaller chunks now, but we recommend waiting until spring to do most dividing. Allow any wounds to callus over by air-drying for a couple of days, after dusting them with a fungicide such as garden sulfur if you have it. Store in covered plastic storage boxes or plastic garbage bags inside cardboard boxes in a cool, dry, dark place, ideally at 40-45° F. Check every now and then. Allow excess moisture to escape (look for condensation) or sprinkle a little water on rhizomes if they seem to be shriveling. You can replant the entire clump in late spring, but if you want to divide it, wait until you’re ready to replant and then break it up by hand or cut it with a sturdy knife. Be sure each division includes a stalk or two. Allow the wounds to dry and callus over for a day or two, after dusting them with a fungicide such as garden sulfur if you have it. Plant outside when all danger of frost is past, the soil has warmed up, and nightly lows are reliably averaging 55° F.
To keep it growing indoors — which is usually a safer bet than storing it dormant — when a killing frost threatens, cut the stalks down to 2-3 feet. Dig and divide into chunks with 1-3 stalks each, if possible dust the wounds with garden sulfur or another fungicide, and pot it up immediately, taking care to preserve as many feeder roots as possible. Set in a warm, sunny window, ideally with a bit of bottom heat. Its growth will slow in winter, so reduce watering and do not fertilize. Your goal is just to keep it alive and growing. In late spring when all danger of frost is past, the soil has warmed up, and nightly lows are reliably averaging 55° F, replant it outside for another summer of amazing beauty.
In zones 8-11 (with lows to +10° F), ‘Ehemanii’ can be left in the ground all winter. Leave the stalks intact and mulch with 6-12 inches of leaves, straw, etc. Thin clumps every few years for best performance.
LEARN MORE about ‘Ehemanii’ at our Spring Diverse Newsletter Archives.