Gardening columnist

The clivia is a handsome houseplant whose leaves are evergreen and straplike. You might buy a pup that in a few years will grow enough leaves to produce a pleasing fan shape. For many gardeners around the world, this is ornament enough. But if you wait until the fan has 13 leaves and give it some tough love, there is a chance that it will suddenly produce a flower stalk that will become topped with a cluster of reddish orange blooms, lilylike and showy.

I have two clivias in a bright, cool room. They are a long way from their ancestors’ native South African forest, but both look healthy, and one is about to flower. When I saw the stalk a couple of weeks ago, well, it’s one of those moments of joy in gardening. There was another, greater thrill to come.

I’m not wired to drop my jaw and say “Wow” when I see something that impresses me, but I might have quietly drooled a bit the other day when I stepped into Alan Petravich’s greenhouse. There, in full bloom, were some 400 mature specimens of clivia. Many are yellow-flowered (this is the brass ring of clivia breeding), and even the orange ones looked special — grading toward red and with striking throat coloration in light yellows.

It’s not actually “his” greenhouse; it belongs to Longwood Gardens in Kennett Square, Pa., but it is here that he manages a clivia research program that dates to 1976.

Amid this stunning assembly of glamour pusses, one looked particularly striking. Tall and with a pair of blooming stalks, it had lustrous green leaves and a sphere composed of blooms. Each blossom was large with full, overlapping petals, and the color was a luscious buttery yellow, darker in the centers. I counted about 20 flowers on one sphere, or umbel, and Petravich drew my attention to the lowest ring of blossoms, young and barely open. They had a green cast to them. We were beholding Longwood’s first and newly introduced variety. Named Longwood Debutante, it sells, he told me, for $899. “Wow.” Give me a moment to close my lower jaw.

Rare clivias have always fetched big prices. An impressive, upright yellow bloomer named Sir John Thouron sold for nearly $1,000 (for charity) when it was released several years ago. Among breeders and growers in California, where pastel colors are favored, it’s not unusual for connoisseurs to pay more than $1,000 a plant, said Petravich.

I wanted to rush home and cuddle my clivias, even if I had bought the mother plant years ago at a mass mechandizer for less than $20. (Petravich said you can probably buy a flowering-size basic clivia today for about $50). Actually, when I did get home, I could see clearly the distinction between my flowering specimen and Longwood Debutante. My plant was smaller, the blooms fewer and not as big. Still, it is cherished, and it responds with flowers.

I had followed the standard clivia cultivation, which is this: After spring blooming, place the potted plant outdoors in a sheltered spot that is in partial to full shade. The pot must drain — don’t place a saucer under it. Keep the clivia watered and lightly fed; that’s about it. If you leave it in a location that gets full sunlight, the leaves will turn a sickening bright yellow and the plant may never recover. Bring it back indoors in October before frost. At that point you treat it like its cousin, the amaryllis. Withhold watering and nutrients and keep it cool; this will cause dormancy needed for flower production in late winter. Plants should be kept under 50 degrees (but above freezing) for 40 days. I close the heat vents in my room, where it stays in the mid-50s through the winter. After this period, raise the temperature to around 60 degrees, resume regular watering, and the flower spike should appear.

Clivias are not like geraniums; they bloom once and for a short period. The flowering can be prolonged by keeping them cool. Petravich’s greenhouse is below 50 degrees and chilly. They are not especially fragrant, alas.

The plants have fleshy roots, almost orchidlike, and they like to be a bit pot-bound. But if the roots are pushing the pot apart, the plant should be repotted after flowering. This also offers the moment to detach the baby clivias, the offsets, and pot them separately.

Mealybugs can be a problem, and the insects get into the leaf crevices and are hard to treat the usual way, with rubbing alcohol on a cotton swab. Some growers use imidacloprid, a systemic insecticide, but I’d be inclined to cover the pot in a plastic bag and then dunk the whole thing in a bath of tepid water.

In the display houses of the East Conservatory at Longwood, many of Petravich’s yellow-flowering clivias have been brought into the flower beds. Along with the blue-flowering Himalayan poppies on show, they’re quite a sight right now, and worth going to see.

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