Answer: Container plants are much more vulnerable to the devastation of summer heat and sun than those planted in the ground. Therefore, you need to provide special care to help them survive -- and more importantly thrive -- during the dog days of summer.
Morning sun is best for flowers and vegetables planted in pots. Most general references for these plants call for a minimum of six hours of direct sunlight. However, our sunlight is so intense that bright indirect light usually is sufficient to encourage good flowering and fruiting. Although you mentioned that your containers were in full sunshine, the following watering practices should help keep the plants from wilting:
In addition to the appropriate location, the amount of water that container plants need also is critical. This is because air circulates around and the sun shines on container sides, so the inside soil dries out rapidly, especially with temperatures exceeding 90 degrees. You may need to water twice daily if plants are in full sun with temperatures more than 100 degrees.
It is a must to water small- and medium-sized containers with such a small volume of soil daily, because they can't hold enough moisture during dry weather. Larger, barrel-sized containers may go a day or two between waterings. You'll know how often to water by the appearance of your plants; if they wilt between waterings, water more often.
Always water enough to thoroughly moisten the soil from top to bottom. Let the water running out the drainage holes be your signal to stop watering.
The plants I've had most success with in hot sunny locations include lantana, ruella, gazania, salvia, Hyptis emoryi (Desert lavender), Lavandula (species Lavender), Leucophyllum laevigatum (Chihuahuan sage) and geraniums.
Best wishes with your garden!
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