Teague: Valley heat takes a toll on flowers

FresnoJuly 26, 2013 

The calla lilies have died back, the lobelia is fried crispy brown, the alstroemeria is producing just a few flowerless stalks, and the impatiens haven't bloomed in a couple of weeks. This is normal during July here in the Central Valley.

Flowering annuals and perennials, and vegetables as well, respond to the intense heat in midsummer by stopping or really slowing bud production.

It's the long, hot nights that cause flowering plants to go into semi-dormancy. Flower production resumes in mid-August as the nights lengthen and nighttime temperatures drop into the lower 60s.

Take an early morning walk around your garden or your neighborhood in July to see which plants are doing better than others. If you want summer color in your garden next year, you'll want to choose plants that continue to flower despite the heat.

Certainly, flowering plants that receive afternoon shade should look healthier than those that must endure 14 hours of full sun.

But location is not the only factor. Some varieties tolerate heat better than others. In my garden, the red-flowered alstroemeria has completely disappeared (no stalks at all) but the larger yellow-flowered variety planted right next to the red continue to push out stalks from the underground tuberous roots. The Pope John Paul tree roses as well as the Passionate Kisses and Trumpeter roses have smaller buds and less vibrant color right now, but they're still flowering while Jardin de Bagatelle, Golden Treasure and Scentimental show no new growth or new buds. The ivy geranium is still in bloom as are the goldenrod and coreopsis, and the yarrow is putting up a second crop of flower stalks.

Fall is our best planting time. When visiting nurseries this September and early October or when ordering seed or transplants from catalogs, check descriptions and labels for terms such as 'heat tolerant' and make sure that the plants are suited for our climate, zones 8 and 9 in the Central Valley and zone 7 in the foothills.

Some newer hybrids of old favorites, including calla lilies and hydrangeas, have been developed to better tolerate long hot summers. Newer calla varieties don't die back completely and will bloom again in fall and newer varieties of hydrangeas bloom all summer long.

Fertilize selectively and lightly in July and into August. Let the semi-dormant varieties have a rest while it's too hot for them to produce buds, but give those plants that are obviously able to produce new growth in summer a light feeding with a lower-nitrogen fertilizer. Higher nitrogen percentages encourage rapid growth of green tissue that can burn in the heat. So I'll be sprinkling a handful or two of a 4-6-2 formulation over the clump of yellow alstroemeria, but wait to feed the now invisible red variety until mid-August.

Elinor Teague is a Fresno County Master Gardener. Send her plant questions at etgrow@comcast.net or features@fresnobee.com ("plants" in the subject line).

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