Answer: Summer sun is indeed stressful for non-native plants. Are they receiving sufficient water? How much to water depends on many factors, such as your soil type, weather, plant maturity, etc. In sandy soil, water will penetrate faster (therefore deeper) but the soil will dry out sooner. In clay soil, it penetrates slower (so not as deep) but it will stay moist longer. Young plants generally need more frequent watering than established plants. Small plants generally need more frequent watering than large (because their root systems are more shallow).
Use the 1-2-3 Rule as an easy method to remember how much to water. Small plants with shallow root systems, such as perennials, veggies, herbs, cacti, succulents have roots that reach about 1 foot deep, so water needs to penetrate that far. When the top 1 inch of soil dries out, it's usually time to water again. Shrubs have root systems that are 2 feet deep so water needs to soak 2 feet deep. When the top 2 inches of soil dries out, it's time to water. Trees are 3 feet, etc. As plants establish root systems, the time between waterings can be lengthened, but it is always essential to water to the same depth. So you are applying the same amount of water with each irrigation regardless of the time of year, but the frequency changes. As warm weather arrives, you need to water more frequently than during winter. For veggies and small plants, it may be necessary to water daily. A soil probe will help you determine how far water has soaked. It moves easily through wet soil but stops when it hits hard soil. If you have drip or soaker hoses, I?d suggest you let it run for 1 hour, then wait an hour or so (for the water to continue penetrating), then use a sharp stick or pointy thing as a soil probe to determine how far the water penetrated in your soil. For most areas, it's necessary to run drip irrigation much longer than people would think.
Be sure to apply several inches of organic mulch around the base of all plants to reduce soil temperatures and maintain moisture. You might also consider erecting a temporary shade cover over your shrubs. Good luck!
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