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Plants

Gardening : Proper Watering a Key to Healthier Petunias

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<i> Guffey is a free-lance writer living in Malibu. </i>

They look pretty in nursery packs and catalogues, and they bloom profusely in Palm Springs, but why do they wilt in my garden? Petunias are perplexing, so I began asking questions.

Kim Bodger of Bodger Seed Co. began my inquiry by describing the development of petunias from the small multiflora types in the ‘50s to the huge grandiflora blooms of the ‘60s and ‘70s.

Breeders fueled the burgeoning bedding-plant industry with petunias that bloomed big and fast. But performance suffered. Bigger flowers didn’t necessarily mean better plants. Enthusiasm for petunias waned. Impatiens, improved through hybridization into super-plants with long bloom and carefree culture, supplanted petunias as the most popular bedding flower.

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Then, according to Bodger, “the petunia industry fought back.” Hybridizers concentrated on more dependable but smaller-flowered types--the old-fashioned multiflora petunias that grew 3 feet tall but managed to bloom all summer without any help. The industry goal was to retain the small petunia’s sturdy constitution and prolific production but create more compact plants. We saw such series as Joy, Comanche, Sugar Plum and Carpet.

Blooms Grew Larger

Hybridizers continued their efforts in the 1980s. The newly designed multiflora petunias exhibited many of the excellent characteristics of the old multifloras, but the blooms were much larger--so large that the name multiflora no longer seemed appropriate. So the petunia industry, like the rose growers, adopted a new generic description for this large-flowered but compact-growing class of petunias: floribunda . In this class, we find the popular Madness series (Summer Madness, Sheer Madness, Coral Madness, etc.). Surprisingly, the new floribunda blooms are almost as large as those of the modern grandifloras (including such series as Daddy, Supercascade, Flash and Supermagic), which are still the largest-selling of all petunia types.

So where does that leave us petunia growers? In my garden the new floribundas are great in pots but in the ground they often wilt, along with the grandfloras and multifloras.

Mike Vukelich Sr., chairman of the board of Color Spot, the largest wholesale nursery of bedding plants in the country, says that the immune system of the petunia isn’t strong enough for moist climates. Petunias succumb to soil viruses. His advice: sterilize the soil. That suggestion brought to mind visions of Chloroxing my flower beds or fumigating them with Vapam, repugnant thoughts indeed, so I pressed him for other ideas. He recommended trying petunias in a different location. In moist climates, he advised placing them in spots where they receive sun for most of the day and good ventilation. Planting them between houses is risky. And watering is critical. With petunias, keep them on the dry side.

Lili Singer, horticultural consultant and radio gardening authority agreed that petunia problems are water related. Petunias are subject to root and crown rot, a result of uneven watering. “Like pansies,” she says, “petunias must never be allowed to wilt, either from under- or overwatering. Once they wilt, it’s all over.” She advises providing good soil conditions, including preparation with organic materials and ample mulching. When watering, do it thoroughly and then allow petunias to dry out--almost to the wilting stage. That appears to be the tricky part--knowing when they are sufficiently dried out.

Susan Brozowski, color specialist at Sherman Gardens in Corona del Mar, says that petunias like it hot and dry. That’s why they thrive in the desert. At Sherman Gardens, where she plants hundreds of petunias in a coastal climate, a liquid fungicide is sometimes used at planting time. But her principal concern, shared by our other authorities, is watering. She warns against watering on a schedule. Always check the soil; if it’s damp, don’t apply water.

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Water and soil fungi often attack petunias as soon as seedlings are transplanted into the ground. This is the time to be most vigilant.

Petunias may develop tiny holes in their blooms, a sign that budworms are present. Geranium and petunia buds are especially attractive to small white moths that lay their eggs at night. These eggs hatch into tiny caterpillars. The best defense is handpicking of the little caterpillars or spraying with B.t., a nontoxic and long-lasting biological control.

To keep my 40 pots of petunias blooming most of the summer, I feed regularly and attempt to remove faded blooms. My petunias in pots provide dependable color for at least 10 weeks before conking out. In the ground, they are a gamble, but hope springs eternal, and next year I’ll try a sunnier location and keep a light hand on the hose.

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