Top-Performing Geraniums In 100-Degree Heat

Top-Performing Geraniums In 100-Degree Heat

Jenny Wegley, research and greenhouse manager at the Dallas Arboretum and Botanical Garden in Dallas, Texas, shares geranium highlights at the arboretum from this past summer.

We have had trouble in the past with geraniums not being able to tolerate the heat and drought conditions of our summers. Over the course of several years, we have seen major changes with heat tolerance and the overall performance in geraniums. With the introduction of interspecifics, there has been a shift in how geraniums perform.

Our historic data shows that almost all varieties tested melted the first day we hit 100°F. They definitely melted if we had nights over 85°F. But recently, we have seen a number of interspecific hybrid geraniums introduced. They have been not only able to tolerate our high day and night temperatures, but they survive longer into the season.

The Caliente and Calliope series, both from Syngenta Flowers, have been two of our best performers for the last four seasons. They both provide nice dark green foliage with a wide selection of bold flower colors. We have seen improvements with ivy types over the past two seasons also, especially with the Cascade series, also from Syngenta Flowers. Cascade has a nice trailing habit with an array of soft colors–usually bicolor with soft green foliage.

The Arboretum’s 2011 Geranium Trial

A look at the types of geraniums trialed this year at the Dallas Arboretum and Botanical Garden in Dallas, Texas. In all, more than 270 different geraniums were trialed.

Pelargonium, Exotic:  5
Pelargonium, Floribunda: 3
Pelargonium, Interspecific: 20
Pelargonium, Ivy: 63
Pelargonium, Scented: 2
Pelargonium, Zonal: 186

All cultivars trialed were vegetative crops and are produced from stick to a quart in five to seven weeks, depending on the weather conditions and the cultivar.

Surprisingly, we have been impressed with Pelargonium x crispum Angeleyes series, from Elsner PAC. This series has a great palate of colors, including bold colors, pastels and bicolors.

A major surprise for us in our recent entries is the Grandirosa series from Dömmen, which is a Regal-type interspecific. Regals, or Martha Washington geraniums, normally don’t live longer than a cut flower bouquet for us, but Grandirosa are still alive even through the second-hottest summer on record in Texas. Although they may not be in flower, it is amazing to us that they have even survived at all.

In our climate, geraniums are not low water-use plants–not now and they probably never will be. Our high day and night temperatures and low humidity require us to keep all geraniums heavily hydrated. We have found all geraniums perform better in containers rather than in the landscape. We have discovered that not only is heavy watering necessary to keep them alive, but also consistent moisture.

Even occasional dry downs in 100°F-plus heat sends even the toughest geraniums in our trials into a death spiral. We’ve found those that are on automated drip survive the longest due to regular and consistent soil moisture. We have to keep in mind trialing material in Dallas means that it might not be pretty all summer long, but if it is not dead it is worthy of notation.

We have a very interested market in Dallas for geraniums, and that will not go away anytime soon. Geraniums tend to remind consumers of their grandparents, parents or childhood events. With the additions of hybrids that can take our heat and still thrive, we think geraniums will be on the consumer’s mind when entering their favorite garden center. Consumers like an array of colors from which to choose. With the addition of so many different colors and foliage shapes, this will encourage the consumer even more.

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