Approaching drought conditions

Its been hot and dry around here... REALLY hot and dry and with no end in sight. Houston is fast approaching official drought conditions if we don't get any rain within the next 10 days. Running the drip irrigation for 15 ~ 20 minutes a day kept the soil in the top of pots moist for a while, but now the moisture meter barely even registers when I probe various areas from top to bottom. So, I turned the drip irrigation on and let it run for two hours this afternoon to try and thoroughly soak the entire pot. Even though their in the shade during the afternoon, I really hope this heat isn't too much for them.