The heat, humidity and winds can dry out several inches of the soil and shallow roots from which they may not recover, and especially recent transplants which would have a better chance of survival if they are planted in close proximity to larger shrubs and plants which can provide some shade relief.
The best defense against this damage is mulch. It protects the surface from sun damage and retains moisture in the soil, which reduces the need for watering.
The easiest mulch to use would be recent grass cuttings. It would be ideal to think ahead and gather the grass cuttings a couple of days after cutting your lawn, when it has dried out somewhat and store a pile of it to distribute over your gardens when heat waves happen. But there are other alternatives to grass cuttings. Light coloured mulches are the best as they will reflect the sunlight and help maintain cooler surface soil.
Some experts recommend Bark Mulch but be warned – depending on what Bark Mulch you use, it might contain weed seeds which may introduce an invasive species into your garden beds that are difficult to eradicate.
Best practice in watering your gardens is to do it early morning. It gives the water a chance to drench the soil before the heat and sun dries it out. Also, it prevents the direct sun from scalding wet plants. Hand watering is preferable in directing the water to the areas that need it the most. In persistent hot weather, a second watering late in the day is advisable.
Another option is soaker hoses that can be placed below the mulch in order to soak the soil directly beneath.
In recent years, we have been experiencing more severe climate changes that will challenge all gardeners, so think ahead and prepare for prolonged heat waves.