Answer: The best heat tolerant annuals are periwinkles, purslane and portulaca. Some of the most heat tolerant perennial plants include:
Purslane: If your planting location is extremely hot, dry and sunny, the best annuals to use are purslane or portulaca. Purslane is available in many colors and produces a mass of color. The large purslane flowers close at 5 p.m., on cloudy days and after watering. Portulaca differs from purslane mainly because it is available only in mixed colors, has a smaller, rose-like bloom and has smaller-leaf foliage.
Verbena: The best perennial verbena is named 'Princess' with 'Blue Princess' being the first in the series. The only way to kill this verbena is to plant it in the shade or keep it too wet. The plants also prosper from periodic abuse -- cut or shred back large plants to remove old blooms and invigorate plants. After such a harsh treatment, the plants may look bad for a couple of weeks. You will reap the rewards of a traffic-stopping bloom display after they regrow and begin to bloom again.
Marigold -Marigolds love hot weather and, except having spider mites occasionally, they are easy to grow. If mites attack, use diazinon, Cygon, Kelthane or disyston to spray the undersides of leaves once a week for three consecutive weeks. One can apply a persistent soil insecticide containing disyston (Systemic Insecticide) after transplanting has occurred to provide prolonged protection. Follow label directions.
Vinca (periwinkle): If full sun conditions exist, vinca is a choice. Vinca thrive in well-drained mixes where liberal amounts of organic material have been added. Water plants during the day and allow them to dry. Water sparingly. If the periwinkle foliage turns yellow, reduce the watering interval and treat plants and soil with iron chelate or iron sulfate.
Lantana: If you want a perennial plant for an extra hot location, try Lantana. The variety named New Gold won't become weed-like as will most of the lantana. New Gold lantana produces sterile flowers that never form seed-bearing berries and continually blooms without shearing. Lantana is also a good plant for a hanging basket in a sunny location. Though Lantana is known as a drought tolerant plant, it requires regular waterings.
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