Heat Makes for Tough Growing Conditions in Louisiana Field Trials

Note: Information for this report was provided by Jeb Fields, Jason Stagg, Ashley Edwards, and Maureen Thiessen of the Hammond Trial Gardens at Louisiana State University.

This was an exceptionally extreme year for our warm season plant trials. The heat arrived quickly in early May, just as the bedding trials were being planted, but then never stopped. Overall, this was the hottest summer on record, with many more days above 100°F than previously recorded. This summer broke records for the most consecutive days with highs at or above 100°F (including total number of days at or above 100°F) and the most consecutive days with record high low temperatures at or above 80°F (and total number of nights at or above 80°F). In addition, this was one of the driest summers on record, with much of our state (including Hammond) in the “exceptional” drought category. The high temps seemed to change other things as well, lowering daytime humidity levels and ushering in a constant breeze. Both of these factors caused the plants to transpire much more than normal.

We trialed about 200 different cultivars this year in our official trialing program, which includes bedding plants, perennials, and some woody shrubs. The Hammond Research Station has a vast collection of other plants in its permanent collection which do not receive trial ratings.

We divide our top performing trial plants into two categories: Blue Chip Winners and Hammond Warm Season Highlights. The Blue Chip winners were the best of the best.

Blue Chip:

Wraps Taken Off USDA’s New Plant Hardiness Zone Map

  • Coleus Down Town Series (Dümmen Orange)
  • Impatiens ‘Beacon Lipstick’ (PanAmerican Seed)
  • Cuphea ‘Sweet Talk Red’ (PanAmerican Seed)
  • Verbena ‘Lascar Orange Lava’ (Selecta One)
  • Crape Myrtle ‘Center Stage Red’ (Proven Winners/Spring Meadow Nursery)

Hammond Warm Season Highlights:

  • Crape Myrtle ‘My Fair Myrtle’ (Star Roses & Plants)
  • Impatiens Solarscape Voodoo Mix (PanAmerican Seed)
  • Ornamental Sweet Potato ‘Sweet Caroline Upside Key Lime’ (Proven Winners)
  • Ornamental Sweet Potato ‘Sweet Caroline Red Hawk’ (Proven Winners)
  • Angelonia ‘Aria Alta Purple’ (Dümmen Orange)
  • Portulaca ‘Cupcake Upright Lavender’ (Dümmen Orange)
  • Salvia ‘Blue By You’ (Darwin Perennials)
  • Kniphofia ‘Glowstick; (Darwin Perennials)
  • El Nino Desert Orchid (Proven Winners)
  • Petunia ‘Sweet Sunshine Pink+Red Vein’ (Selecta One)
  • Calibrachoa ‘Superbells Prism Pink Lemonade’ (Proven Winners)
  • Calibrachoa ‘Superbells Pink 2024’ (Proven Winners)

The weather was the biggest wild card in our trials this year. It was nice to see some things thriving no matter how hot it was (lantana, coleus, ornamental sweet potatoes, etc.), but the weather also cut short the lives of many beautiful plants. Consistent hot temperatures prevented some plants, especially perennials, from establishing and performing well. Although irrigation was increased over the amount a normal summer would call for, we still lost some plants early on. The heat was so intense that many plants experienced leaf scorch or complete defoliation. On the other hand, species that normally melt under our rainy and humid summers performed better than expected. At the end of the trialing season, the survivors were overwhelmingly of tropical or sub-tropical origin.

In terms of the plants that impressed us the most, Proven Winners’ El Nino Desert Orchid has been the most unusual and most talked about plant this trialing season. Although the specimens were planted in May, they have shrugged off the extreme heat as if it never happened. There was no leaf scorch, the plants grew quickly, and they have been blooming off and on all summer. The blooms are showy and wonderfully fragrant. We love this plant!

Dümmen Orange sent numerous cultivars in its new Down Town coleus series. We truly appreciated the perfect size of this series: showy, but not too big or brittle. The growth habit was bushy and full, and the more narrow serrated leaf shape added good texture to the landscape. All but one cultivar bloomed late in the season, demonstrating good resilience in a long, tough growing season. We trialed NYC Nights, Greenville, Vegas Neon, Miami Magic, and Greenville.

From Ball’s PanAmerican Seed division, we received the new Sweet Talk cuphea Series. The cultivar simply named Red was our favorite, as it had the showiest flowers. Deep Pink was a close second, as both colors appeared quite similar in our trials. The large, bat-faced flowers were held mostly upright on smaller plants with small leaves, making the blooms easy to spot in the landscape. Although the extreme heat caused this series to bow out a little early, we still loved it for some of the largest bat-faced flowers we’ve seen survive in our trials.

Click here for results from more 2023 field trials.

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